2 * CAM IO Scheduler Interface
4 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
6 * Copyright (c) 2015 Netflix, Inc.
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions, and the following disclaimer,
13 * without modification, immediately at the beginning of the file.
14 * 2. The name of the author may not be used to endorse or promote products
15 * derived from this software without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
21 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
38 #include <sys/param.h>
40 #include <sys/systm.h>
41 #include <sys/kernel.h>
44 #include <sys/malloc.h>
45 #include <sys/mutex.h>
47 #include <sys/sysctl.h>
50 #include <cam/cam_ccb.h>
51 #include <cam/cam_periph.h>
52 #include <cam/cam_xpt_periph.h>
53 #include <cam/cam_xpt_internal.h>
54 #include <cam/cam_iosched.h>
58 static MALLOC_DEFINE(M_CAMSCHED, "CAM I/O Scheduler",
59 "CAM I/O Scheduler buffers");
62 * Default I/O scheduler for FreeBSD. This implementation is just a thin-vineer
63 * over the bioq_* interface, with notions of separate calls for normal I/O and
66 * When CAM_IOSCHED_DYNAMIC is defined, the scheduler is enhanced to dynamically
67 * steer the rate of one type of traffic to help other types of traffic (eg
68 * limit writes when read latency deteriorates on SSDs).
71 #ifdef CAM_IOSCHED_DYNAMIC
73 static int do_dynamic_iosched = 1;
74 TUNABLE_INT("kern.cam.do_dynamic_iosched", &do_dynamic_iosched);
75 SYSCTL_INT(_kern_cam, OID_AUTO, do_dynamic_iosched, CTLFLAG_RD,
76 &do_dynamic_iosched, 1,
77 "Enable Dynamic I/O scheduler optimizations.");
80 * For an EMA, with an alpha of alpha, we know
84 * where N is the number of samples that 86% of the current
85 * EMA is derived from.
87 * So we invent[*] alpha_bits:
88 * alpha_bits = -log_2(alpha)
89 * alpha = 2^-alpha_bits
91 * N = 1 + 2^(alpha_bits + 1)
93 * The default 9 gives a 1025 lookback for 86% of the data.
94 * For a brief intro: https://en.wikipedia.org/wiki/Moving_average
96 * [*] Steal from the load average code and many other places.
97 * Note: See computation of EMA and EMVAR for acceptable ranges of alpha.
99 static int alpha_bits = 9;
100 TUNABLE_INT("kern.cam.iosched_alpha_bits", &alpha_bits);
101 SYSCTL_INT(_kern_cam, OID_AUTO, iosched_alpha_bits, CTLFLAG_RW,
103 "Bits in EMA's alpha.");
106 struct cam_iosched_softc;
108 int iosched_debug = 0;
111 none = 0, /* No limits */
112 queue_depth, /* Limit how many ops we queue to SIM */
113 iops, /* Limit # of IOPS to the drive */
114 bandwidth, /* Limit bandwidth to the drive */
118 static const char *cam_iosched_limiter_names[] =
119 { "none", "queue_depth", "iops", "bandwidth" };
122 * Called to initialize the bits of the iop_stats structure relevant to the
123 * limiter. Called just after the limiter is set.
125 typedef int l_init_t(struct iop_stats *);
130 typedef int l_tick_t(struct iop_stats *);
133 * Called to see if the limiter thinks this IOP can be allowed to
134 * proceed. If so, the limiter assumes that the IOP proceeded
135 * and makes any accounting of it that's needed.
137 typedef int l_iop_t(struct iop_stats *, struct bio *);
140 * Called when an I/O completes so the limiter can update its
141 * accounting. Pending I/Os may complete in any order (even when
142 * sent to the hardware at the same time), so the limiter may not
143 * make any assumptions other than this I/O has completed. If it
144 * returns 1, then xpt_schedule() needs to be called again.
146 typedef int l_iodone_t(struct iop_stats *, struct bio *);
148 static l_iop_t cam_iosched_qd_iop;
149 static l_iop_t cam_iosched_qd_caniop;
150 static l_iodone_t cam_iosched_qd_iodone;
152 static l_init_t cam_iosched_iops_init;
153 static l_tick_t cam_iosched_iops_tick;
154 static l_iop_t cam_iosched_iops_caniop;
155 static l_iop_t cam_iosched_iops_iop;
157 static l_init_t cam_iosched_bw_init;
158 static l_tick_t cam_iosched_bw_tick;
159 static l_iop_t cam_iosched_bw_caniop;
160 static l_iop_t cam_iosched_bw_iop;
167 l_iodone_t *l_iodone;
179 .l_caniop = cam_iosched_qd_caniop,
180 .l_iop = cam_iosched_qd_iop,
181 .l_iodone= cam_iosched_qd_iodone,
184 .l_init = cam_iosched_iops_init,
185 .l_tick = cam_iosched_iops_tick,
186 .l_caniop = cam_iosched_iops_caniop,
187 .l_iop = cam_iosched_iops_iop,
191 .l_init = cam_iosched_bw_init,
192 .l_tick = cam_iosched_bw_tick,
193 .l_caniop = cam_iosched_bw_caniop,
194 .l_iop = cam_iosched_bw_iop,
201 * sysctl state for this subnode.
203 struct sysctl_ctx_list sysctl_ctx;
204 struct sysctl_oid *sysctl_tree;
207 * Information about the current rate limiters, if any
209 io_limiter limiter; /* How are I/Os being limited */
210 int min; /* Low range of limit */
211 int max; /* High range of limit */
212 int current; /* Current rate limiter */
213 int l_value1; /* per-limiter scratch value 1. */
214 int l_value2; /* per-limiter scratch value 2. */
217 * Debug information about counts of I/Os that have gone through the
220 int pending; /* I/Os pending in the hardware */
221 int queued; /* number currently in the queue */
222 int total; /* Total for all time -- wraps */
223 int in; /* number queued all time -- wraps */
224 int out; /* number completed all time -- wraps */
225 int errs; /* Number of I/Os completed with error -- wraps */
228 * Statistics on different bits of the process.
230 /* Exp Moving Average, see alpha_bits for more details */
233 sbintime_t sd; /* Last computed sd */
235 uint32_t state_flags;
236 #define IOP_RATE_LIMITED 1u
238 #define LAT_BUCKETS 15 /* < 1ms < 2ms ... < 2^(n-1)ms >= 2^(n-1)ms*/
239 uint64_t latencies[LAT_BUCKETS];
241 struct cam_iosched_softc *softc;
246 set_max = 0, /* current = max */
247 read_latency, /* Steer read latency by throttling writes */
248 cl_max /* Keep last */
251 static const char *cam_iosched_control_type_names[] =
252 { "set_max", "read_latency" };
254 struct control_loop {
256 * sysctl state for this subnode.
258 struct sysctl_ctx_list sysctl_ctx;
259 struct sysctl_oid *sysctl_tree;
261 sbintime_t next_steer; /* Time of next steer */
262 sbintime_t steer_interval; /* How often do we steer? */
266 control_type type; /* What type of control? */
267 int last_count; /* Last I/O count */
269 struct cam_iosched_softc *softc;
274 struct cam_iosched_softc {
275 struct bio_queue_head bio_queue;
276 struct bio_queue_head trim_queue;
277 /* scheduler flags < 16, user flags >= 16 */
280 #ifdef CAM_IOSCHED_DYNAMIC
281 int read_bias; /* Read bias setting */
282 int current_read_bias; /* Current read bias state */
284 int load; /* EMA of 'load average' of disk / 2^16 */
286 struct bio_queue_head write_queue;
287 struct iop_stats read_stats, write_stats, trim_stats;
288 struct sysctl_ctx_list sysctl_ctx;
289 struct sysctl_oid *sysctl_tree;
291 int quanta; /* Number of quanta per second */
292 struct callout ticker; /* Callout for our quota system */
293 struct cam_periph *periph; /* cam periph associated with this device */
294 uint32_t this_frac; /* Fraction of a second (1024ths) for this tick */
295 sbintime_t last_time; /* Last time we ticked */
296 struct control_loop cl;
297 sbintime_t max_lat; /* when != 0, if iop latency > max_lat, call max_lat_fcn */
298 cam_iosched_latfcn_t latfcn;
303 #ifdef CAM_IOSCHED_DYNAMIC
305 * helper functions to call the limsw functions.
308 cam_iosched_limiter_init(struct iop_stats *ios)
310 int lim = ios->limiter;
312 /* maybe this should be a kassert */
313 if (lim < none || lim >= limiter_max)
316 if (limsw[lim].l_init)
317 return limsw[lim].l_init(ios);
323 cam_iosched_limiter_tick(struct iop_stats *ios)
325 int lim = ios->limiter;
327 /* maybe this should be a kassert */
328 if (lim < none || lim >= limiter_max)
331 if (limsw[lim].l_tick)
332 return limsw[lim].l_tick(ios);
338 cam_iosched_limiter_iop(struct iop_stats *ios, struct bio *bp)
340 int lim = ios->limiter;
342 /* maybe this should be a kassert */
343 if (lim < none || lim >= limiter_max)
346 if (limsw[lim].l_iop)
347 return limsw[lim].l_iop(ios, bp);
353 cam_iosched_limiter_caniop(struct iop_stats *ios, struct bio *bp)
355 int lim = ios->limiter;
357 /* maybe this should be a kassert */
358 if (lim < none || lim >= limiter_max)
361 if (limsw[lim].l_caniop)
362 return limsw[lim].l_caniop(ios, bp);
368 cam_iosched_limiter_iodone(struct iop_stats *ios, struct bio *bp)
370 int lim = ios->limiter;
372 /* maybe this should be a kassert */
373 if (lim < none || lim >= limiter_max)
376 if (limsw[lim].l_iodone)
377 return limsw[lim].l_iodone(ios, bp);
383 * Functions to implement the different kinds of limiters
387 cam_iosched_qd_iop(struct iop_stats *ios, struct bio *bp)
390 if (ios->current <= 0 || ios->pending < ios->current)
397 cam_iosched_qd_caniop(struct iop_stats *ios, struct bio *bp)
400 if (ios->current <= 0 || ios->pending < ios->current)
407 cam_iosched_qd_iodone(struct iop_stats *ios, struct bio *bp)
410 if (ios->current <= 0 || ios->pending != ios->current)
417 cam_iosched_iops_init(struct iop_stats *ios)
420 ios->l_value1 = ios->current / ios->softc->quanta;
421 if (ios->l_value1 <= 0)
429 cam_iosched_iops_tick(struct iop_stats *ios)
434 * Allow at least one IO per tick until all
435 * the IOs for this interval have been spent.
437 new_ios = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
438 if (new_ios < 1 && ios->l_value2 < ios->current) {
444 * If this a new accounting interval, discard any "unspent" ios
445 * granted in the previous interval. Otherwise add the new ios to
446 * the previously granted ones that haven't been spent yet.
448 if ((ios->softc->total_ticks % ios->softc->quanta) == 0) {
449 ios->l_value1 = new_ios;
452 ios->l_value1 += new_ios;
460 cam_iosched_iops_caniop(struct iop_stats *ios, struct bio *bp)
464 * So if we have any more IOPs left, allow it,
465 * otherwise wait. If current iops is 0, treat that
466 * as unlimited as a failsafe.
468 if (ios->current > 0 && ios->l_value1 <= 0)
474 cam_iosched_iops_iop(struct iop_stats *ios, struct bio *bp)
478 rv = cam_iosched_limiter_caniop(ios, bp);
486 cam_iosched_bw_init(struct iop_stats *ios)
489 /* ios->current is in kB/s, so scale to bytes */
490 ios->l_value1 = ios->current * 1000 / ios->softc->quanta;
496 cam_iosched_bw_tick(struct iop_stats *ios)
501 * If we're in the hole for available quota from
502 * the last time, then add the quantum for this.
503 * If we have any left over from last quantum,
504 * then too bad, that's lost. Also, ios->current
505 * is in kB/s, so scale.
507 * We also allow up to 4 quanta of credits to
508 * accumulate to deal with burstiness. 4 is extremely
511 bw = (int)((ios->current * 1000ull * (uint64_t)ios->softc->this_frac) >> 16);
512 if (ios->l_value1 < bw * 4)
519 cam_iosched_bw_caniop(struct iop_stats *ios, struct bio *bp)
522 * So if we have any more bw quota left, allow it,
523 * otherwise wait. Note, we'll go negative and that's
524 * OK. We'll just get a little less next quota.
526 * Note on going negative: that allows us to process
527 * requests in order better, since we won't allow
528 * shorter reads to get around the long one that we
529 * don't have the quota to do just yet. It also prevents
530 * starvation by being a little more permissive about
531 * what we let through this quantum (to prevent the
532 * starvation), at the cost of getting a little less
535 * Also note that if the current limit is <= 0,
536 * we treat it as unlimited as a failsafe.
538 if (ios->current > 0 && ios->l_value1 <= 0)
546 cam_iosched_bw_iop(struct iop_stats *ios, struct bio *bp)
550 rv = cam_iosched_limiter_caniop(ios, bp);
552 ios->l_value1 -= bp->bio_length;
557 static void cam_iosched_cl_maybe_steer(struct control_loop *clp);
560 cam_iosched_ticker(void *arg)
562 struct cam_iosched_softc *isc = arg;
563 sbintime_t now, delta;
566 callout_reset(&isc->ticker, hz / isc->quanta, cam_iosched_ticker, isc);
569 delta = now - isc->last_time;
570 isc->this_frac = (uint32_t)delta >> 16; /* Note: discards seconds -- should be 0 harmless if not */
571 isc->last_time = now;
573 cam_iosched_cl_maybe_steer(&isc->cl);
575 cam_iosched_limiter_tick(&isc->read_stats);
576 cam_iosched_limiter_tick(&isc->write_stats);
577 cam_iosched_limiter_tick(&isc->trim_stats);
579 cam_iosched_schedule(isc, isc->periph);
582 * isc->load is an EMA of the pending I/Os at each tick. The number of
583 * pending I/Os is the sum of the I/Os queued to the hardware, and those
584 * in the software queue that could be queued to the hardware if there
587 * ios_stats.pending is a count of requests in the SIM right now for
588 * each of these types of I/O. So the total pending count is the sum of
589 * these I/Os and the sum of the queued I/Os still in the software queue
590 * for those operations that aren't being rate limited at the moment.
592 * The reason for the rate limiting bit is because those I/Os
593 * aren't part of the software queued load (since we could
594 * give them to hardware, but choose not to).
596 * Note: due to a bug in counting pending TRIM in the device, we
597 * don't include them in this count. We count each BIO_DELETE in
598 * the pending count, but the periph drivers collapse them down
599 * into one TRIM command. That one trim command gets the completion
600 * so the counts get off.
602 pending = isc->read_stats.pending + isc->write_stats.pending /* + isc->trim_stats.pending */;
603 pending += !!(isc->read_stats.state_flags & IOP_RATE_LIMITED) * isc->read_stats.queued +
604 !!(isc->write_stats.state_flags & IOP_RATE_LIMITED) * isc->write_stats.queued /* +
605 !!(isc->trim_stats.state_flags & IOP_RATE_LIMITED) * isc->trim_stats.queued */ ;
607 pending /= isc->periph->path->device->ccbq.total_openings;
609 isc->load = (pending + (isc->load << 13) - isc->load) >> 13; /* see above: 13 -> 16139 / 200/s = ~81s ~1 minute */
616 cam_iosched_cl_init(struct control_loop *clp, struct cam_iosched_softc *isc)
619 clp->next_steer = sbinuptime();
621 clp->steer_interval = SBT_1S * 5; /* Let's start out steering every 5s */
622 clp->lolat = 5 * SBT_1MS;
623 clp->hilat = 15 * SBT_1MS;
624 clp->alpha = 20; /* Alpha == gain. 20 = .2 */
629 cam_iosched_cl_maybe_steer(struct control_loop *clp)
631 struct cam_iosched_softc *isc;
636 now = isc->last_time;
637 if (now < clp->next_steer)
640 clp->next_steer = now + clp->steer_interval;
643 if (isc->write_stats.current != isc->write_stats.max)
644 printf("Steering write from %d kBps to %d kBps\n",
645 isc->write_stats.current, isc->write_stats.max);
646 isc->read_stats.current = isc->read_stats.max;
647 isc->write_stats.current = isc->write_stats.max;
648 isc->trim_stats.current = isc->trim_stats.max;
651 old = isc->write_stats.current;
652 lat = isc->read_stats.ema;
654 * Simple PLL-like engine. Since we're steering to a range for
655 * the SP (set point) that makes things a little more
656 * complicated. In addition, we're not directly controlling our
657 * PV (process variable), the read latency, but instead are
658 * manipulating the write bandwidth limit for our MV
659 * (manipulation variable), analysis of this code gets a bit
660 * messy. Also, the MV is a very noisy control surface for read
661 * latency since it is affected by many hidden processes inside
662 * the device which change how responsive read latency will be
663 * in reaction to changes in write bandwidth. Unlike the classic
664 * boiler control PLL. this may result in over-steering while
665 * the SSD takes its time to react to the new, lower load. This
666 * is why we use a relatively low alpha of between .1 and .25 to
667 * compensate for this effect. At .1, it takes ~22 steering
668 * intervals to back off by a factor of 10. At .2 it only takes
669 * ~10. At .25 it only takes ~8. However some preliminary data
670 * from the SSD drives suggests a reasponse time in 10's of
671 * seconds before latency drops regardless of the new write
672 * rate. Careful observation will be required to tune this
675 * Also, when there's no read traffic, we jack up the write
676 * limit too regardless of the last read latency. 10 is
677 * somewhat arbitrary.
679 if (lat < clp->lolat || isc->read_stats.total - clp->last_count < 10)
680 isc->write_stats.current = isc->write_stats.current *
681 (100 + clp->alpha) / 100; /* Scale up */
682 else if (lat > clp->hilat)
683 isc->write_stats.current = isc->write_stats.current *
684 (100 - clp->alpha) / 100; /* Scale down */
685 clp->last_count = isc->read_stats.total;
688 * Even if we don't steer, per se, enforce the min/max limits as
689 * those may have changed.
691 if (isc->write_stats.current < isc->write_stats.min)
692 isc->write_stats.current = isc->write_stats.min;
693 if (isc->write_stats.current > isc->write_stats.max)
694 isc->write_stats.current = isc->write_stats.max;
695 if (old != isc->write_stats.current && iosched_debug)
696 printf("Steering write from %d kBps to %d kBps due to latency of %jdus\n",
697 old, isc->write_stats.current,
698 (uintmax_t)((uint64_t)1000000 * (uint32_t)lat) >> 32);
707 * Trim or similar currently pending completion. Should only be set for
708 * those drivers wishing only one Trim active at a time.
710 #define CAM_IOSCHED_FLAG_TRIM_ACTIVE (1ul << 0)
711 /* Callout active, and needs to be torn down */
712 #define CAM_IOSCHED_FLAG_CALLOUT_ACTIVE (1ul << 1)
714 /* Periph drivers set these flags to indicate work */
715 #define CAM_IOSCHED_FLAG_WORK_FLAGS ((0xffffu) << 16)
717 #ifdef CAM_IOSCHED_DYNAMIC
719 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
720 sbintime_t sim_latency, int cmd, size_t size);
724 cam_iosched_has_flagged_work(struct cam_iosched_softc *isc)
726 return !!(isc->flags & CAM_IOSCHED_FLAG_WORK_FLAGS);
730 cam_iosched_has_io(struct cam_iosched_softc *isc)
732 #ifdef CAM_IOSCHED_DYNAMIC
733 if (do_dynamic_iosched) {
734 struct bio *rbp = bioq_first(&isc->bio_queue);
735 struct bio *wbp = bioq_first(&isc->write_queue);
736 bool can_write = wbp != NULL &&
737 cam_iosched_limiter_caniop(&isc->write_stats, wbp) == 0;
738 bool can_read = rbp != NULL &&
739 cam_iosched_limiter_caniop(&isc->read_stats, rbp) == 0;
740 if (iosched_debug > 2) {
741 printf("can write %d: pending_writes %d max_writes %d\n", can_write, isc->write_stats.pending, isc->write_stats.max);
742 printf("can read %d: read_stats.pending %d max_reads %d\n", can_read, isc->read_stats.pending, isc->read_stats.max);
743 printf("Queued reads %d writes %d\n", isc->read_stats.queued, isc->write_stats.queued);
745 return can_read || can_write;
748 return bioq_first(&isc->bio_queue) != NULL;
752 cam_iosched_has_more_trim(struct cam_iosched_softc *isc)
754 return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) &&
755 bioq_first(&isc->trim_queue);
758 #define cam_iosched_sort_queue(isc) ((isc)->sort_io_queue >= 0 ? \
759 (isc)->sort_io_queue : cam_sort_io_queues)
763 cam_iosched_has_work(struct cam_iosched_softc *isc)
765 #ifdef CAM_IOSCHED_DYNAMIC
766 if (iosched_debug > 2)
767 printf("has work: %d %d %d\n", cam_iosched_has_io(isc),
768 cam_iosched_has_more_trim(isc),
769 cam_iosched_has_flagged_work(isc));
772 return cam_iosched_has_io(isc) ||
773 cam_iosched_has_more_trim(isc) ||
774 cam_iosched_has_flagged_work(isc);
777 #ifdef CAM_IOSCHED_DYNAMIC
779 cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios)
784 ios->max = ios->current = 300000;
794 cam_iosched_limiter_init(ios);
798 cam_iosched_limiter_sysctl(SYSCTL_HANDLER_ARGS)
801 struct iop_stats *ios;
802 struct cam_iosched_softc *isc;
808 value = ios->limiter;
809 if (value < none || value >= limiter_max)
812 p = cam_iosched_limiter_names[value];
814 strlcpy(buf, p, sizeof(buf));
815 error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
816 if (error != 0 || req->newptr == NULL)
819 cam_periph_lock(isc->periph);
821 for (i = none; i < limiter_max; i++) {
822 if (strcmp(buf, cam_iosched_limiter_names[i]) != 0)
825 error = cam_iosched_limiter_init(ios);
827 ios->limiter = value;
828 cam_periph_unlock(isc->periph);
831 /* Note: disk load averate requires ticker to be always running */
832 callout_reset(&isc->ticker, hz / isc->quanta, cam_iosched_ticker, isc);
833 isc->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
835 cam_periph_unlock(isc->periph);
839 cam_periph_unlock(isc->periph);
844 cam_iosched_control_type_sysctl(SYSCTL_HANDLER_ARGS)
847 struct control_loop *clp;
848 struct cam_iosched_softc *isc;
855 if (value < none || value >= cl_max)
858 p = cam_iosched_control_type_names[value];
860 strlcpy(buf, p, sizeof(buf));
861 error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
862 if (error != 0 || req->newptr == NULL)
865 for (i = set_max; i < cl_max; i++) {
866 if (strcmp(buf, cam_iosched_control_type_names[i]) != 0)
868 cam_periph_lock(isc->periph);
870 cam_periph_unlock(isc->periph);
878 cam_iosched_sbintime_sysctl(SYSCTL_HANDLER_ARGS)
885 value = *(sbintime_t *)arg1;
886 us = (uint64_t)value / SBT_1US;
887 snprintf(buf, sizeof(buf), "%ju", (intmax_t)us);
888 error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
889 if (error != 0 || req->newptr == NULL)
891 us = strtoul(buf, NULL, 10);
894 *(sbintime_t *)arg1 = us * SBT_1US;
899 cam_iosched_sysctl_latencies(SYSCTL_HANDLER_ARGS)
906 sbuf_new_for_sysctl(&sb, NULL, LAT_BUCKETS * 16, req);
908 for (i = 0; i < LAT_BUCKETS - 1; i++)
909 sbuf_printf(&sb, "%jd,", (intmax_t)latencies[i]);
910 sbuf_printf(&sb, "%jd", (intmax_t)latencies[LAT_BUCKETS - 1]);
911 error = sbuf_finish(&sb);
918 cam_iosched_quanta_sysctl(SYSCTL_HANDLER_ARGS)
923 quanta = (unsigned *)arg1;
926 error = sysctl_handle_int(oidp, (int *)&value, 0, req);
927 if ((error != 0) || (req->newptr == NULL))
930 if (value < 1 || value > hz)
939 cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stats *ios, char *name)
941 struct sysctl_oid_list *n;
942 struct sysctl_ctx_list *ctx;
944 ios->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
945 SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, name,
946 CTLFLAG_RD, 0, name);
947 n = SYSCTL_CHILDREN(ios->sysctl_tree);
948 ctx = &ios->sysctl_ctx;
950 SYSCTL_ADD_UQUAD(ctx, n,
951 OID_AUTO, "ema", CTLFLAG_RD,
953 "Fast Exponentially Weighted Moving Average");
954 SYSCTL_ADD_UQUAD(ctx, n,
955 OID_AUTO, "emvar", CTLFLAG_RD,
957 "Fast Exponentially Weighted Moving Variance");
959 SYSCTL_ADD_INT(ctx, n,
960 OID_AUTO, "pending", CTLFLAG_RD,
962 "Instantaneous # of pending transactions");
963 SYSCTL_ADD_INT(ctx, n,
964 OID_AUTO, "count", CTLFLAG_RD,
966 "# of transactions submitted to hardware");
967 SYSCTL_ADD_INT(ctx, n,
968 OID_AUTO, "queued", CTLFLAG_RD,
970 "# of transactions in the queue");
971 SYSCTL_ADD_INT(ctx, n,
972 OID_AUTO, "in", CTLFLAG_RD,
974 "# of transactions queued to driver");
975 SYSCTL_ADD_INT(ctx, n,
976 OID_AUTO, "out", CTLFLAG_RD,
978 "# of transactions completed (including with error)");
979 SYSCTL_ADD_INT(ctx, n,
980 OID_AUTO, "errs", CTLFLAG_RD,
982 "# of transactions completed with an error");
984 SYSCTL_ADD_PROC(ctx, n,
985 OID_AUTO, "limiter", CTLTYPE_STRING | CTLFLAG_RW,
986 ios, 0, cam_iosched_limiter_sysctl, "A",
987 "Current limiting type.");
988 SYSCTL_ADD_INT(ctx, n,
989 OID_AUTO, "min", CTLFLAG_RW,
992 SYSCTL_ADD_INT(ctx, n,
993 OID_AUTO, "max", CTLFLAG_RW,
996 SYSCTL_ADD_INT(ctx, n,
997 OID_AUTO, "current", CTLFLAG_RW,
1001 SYSCTL_ADD_PROC(ctx, n,
1002 OID_AUTO, "latencies", CTLTYPE_STRING | CTLFLAG_RD,
1004 cam_iosched_sysctl_latencies, "A",
1005 "Array of power of 2 latency from 1ms to 1.024s");
1009 cam_iosched_iop_stats_fini(struct iop_stats *ios)
1011 if (ios->sysctl_tree)
1012 if (sysctl_ctx_free(&ios->sysctl_ctx) != 0)
1013 printf("can't remove iosched sysctl stats context\n");
1017 cam_iosched_cl_sysctl_init(struct cam_iosched_softc *isc)
1019 struct sysctl_oid_list *n;
1020 struct sysctl_ctx_list *ctx;
1021 struct control_loop *clp;
1024 clp->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
1025 SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, "control",
1026 CTLFLAG_RD, 0, "Control loop info");
1027 n = SYSCTL_CHILDREN(clp->sysctl_tree);
1028 ctx = &clp->sysctl_ctx;
1030 SYSCTL_ADD_PROC(ctx, n,
1031 OID_AUTO, "type", CTLTYPE_STRING | CTLFLAG_RW,
1032 clp, 0, cam_iosched_control_type_sysctl, "A",
1033 "Control loop algorithm");
1034 SYSCTL_ADD_PROC(ctx, n,
1035 OID_AUTO, "steer_interval", CTLTYPE_STRING | CTLFLAG_RW,
1036 &clp->steer_interval, 0, cam_iosched_sbintime_sysctl, "A",
1037 "How often to steer (in us)");
1038 SYSCTL_ADD_PROC(ctx, n,
1039 OID_AUTO, "lolat", CTLTYPE_STRING | CTLFLAG_RW,
1040 &clp->lolat, 0, cam_iosched_sbintime_sysctl, "A",
1041 "Low water mark for Latency (in us)");
1042 SYSCTL_ADD_PROC(ctx, n,
1043 OID_AUTO, "hilat", CTLTYPE_STRING | CTLFLAG_RW,
1044 &clp->hilat, 0, cam_iosched_sbintime_sysctl, "A",
1045 "Hi water mark for Latency (in us)");
1046 SYSCTL_ADD_INT(ctx, n,
1047 OID_AUTO, "alpha", CTLFLAG_RW,
1049 "Alpha for PLL (x100) aka gain");
1053 cam_iosched_cl_sysctl_fini(struct control_loop *clp)
1055 if (clp->sysctl_tree)
1056 if (sysctl_ctx_free(&clp->sysctl_ctx) != 0)
1057 printf("can't remove iosched sysctl control loop context\n");
1062 * Allocate the iosched structure. This also insulates callers from knowing
1063 * sizeof struct cam_iosched_softc.
1066 cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph)
1069 *iscp = malloc(sizeof(**iscp), M_CAMSCHED, M_NOWAIT | M_ZERO);
1072 #ifdef CAM_IOSCHED_DYNAMIC
1074 printf("CAM IOSCHEDULER Allocating entry at %p\n", *iscp);
1076 (*iscp)->sort_io_queue = -1;
1077 bioq_init(&(*iscp)->bio_queue);
1078 bioq_init(&(*iscp)->trim_queue);
1079 #ifdef CAM_IOSCHED_DYNAMIC
1080 if (do_dynamic_iosched) {
1081 bioq_init(&(*iscp)->write_queue);
1082 (*iscp)->read_bias = 100;
1083 (*iscp)->current_read_bias = 100;
1084 (*iscp)->quanta = min(hz, 200);
1085 cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats);
1086 cam_iosched_iop_stats_init(*iscp, &(*iscp)->write_stats);
1087 cam_iosched_iop_stats_init(*iscp, &(*iscp)->trim_stats);
1088 (*iscp)->trim_stats.max = 1; /* Trims are special: one at a time for now */
1089 (*iscp)->last_time = sbinuptime();
1090 callout_init_mtx(&(*iscp)->ticker, cam_periph_mtx(periph), 0);
1091 (*iscp)->periph = periph;
1092 cam_iosched_cl_init(&(*iscp)->cl, *iscp);
1093 callout_reset(&(*iscp)->ticker, hz / (*iscp)->quanta, cam_iosched_ticker, *iscp);
1094 (*iscp)->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
1102 * Reclaim all used resources. This assumes that other folks have
1103 * drained the requests in the hardware. Maybe an unwise assumption.
1106 cam_iosched_fini(struct cam_iosched_softc *isc)
1109 cam_iosched_flush(isc, NULL, ENXIO);
1110 #ifdef CAM_IOSCHED_DYNAMIC
1111 cam_iosched_iop_stats_fini(&isc->read_stats);
1112 cam_iosched_iop_stats_fini(&isc->write_stats);
1113 cam_iosched_iop_stats_fini(&isc->trim_stats);
1114 cam_iosched_cl_sysctl_fini(&isc->cl);
1115 if (isc->sysctl_tree)
1116 if (sysctl_ctx_free(&isc->sysctl_ctx) != 0)
1117 printf("can't remove iosched sysctl stats context\n");
1118 if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) {
1119 callout_drain(&isc->ticker);
1120 isc->flags &= ~ CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
1123 free(isc, M_CAMSCHED);
1128 * After we're sure we're attaching a device, go ahead and add
1129 * hooks for any sysctl we may wish to honor.
1131 void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
1132 struct sysctl_ctx_list *ctx, struct sysctl_oid *node)
1134 #ifdef CAM_IOSCHED_DYNAMIC
1135 struct sysctl_oid_list *n;
1138 SYSCTL_ADD_INT(ctx, SYSCTL_CHILDREN(node),
1139 OID_AUTO, "sort_io_queue", CTLFLAG_RW | CTLFLAG_MPSAFE,
1140 &isc->sort_io_queue, 0,
1141 "Sort IO queue to try and optimise disk access patterns");
1143 #ifdef CAM_IOSCHED_DYNAMIC
1144 if (!do_dynamic_iosched)
1147 isc->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
1148 SYSCTL_CHILDREN(node), OID_AUTO, "iosched",
1149 CTLFLAG_RD, 0, "I/O scheduler statistics");
1150 n = SYSCTL_CHILDREN(isc->sysctl_tree);
1151 ctx = &isc->sysctl_ctx;
1153 cam_iosched_iop_stats_sysctl_init(isc, &isc->read_stats, "read");
1154 cam_iosched_iop_stats_sysctl_init(isc, &isc->write_stats, "write");
1155 cam_iosched_iop_stats_sysctl_init(isc, &isc->trim_stats, "trim");
1156 cam_iosched_cl_sysctl_init(isc);
1158 SYSCTL_ADD_INT(ctx, n,
1159 OID_AUTO, "read_bias", CTLFLAG_RW,
1160 &isc->read_bias, 100,
1161 "How biased towards read should we be independent of limits");
1163 SYSCTL_ADD_PROC(ctx, n,
1164 OID_AUTO, "quanta", CTLTYPE_UINT | CTLFLAG_RW,
1165 &isc->quanta, 0, cam_iosched_quanta_sysctl, "I",
1166 "How many quanta per second do we slice the I/O up into");
1168 SYSCTL_ADD_INT(ctx, n,
1169 OID_AUTO, "total_ticks", CTLFLAG_RD,
1170 &isc->total_ticks, 0,
1171 "Total number of ticks we've done");
1173 SYSCTL_ADD_INT(ctx, n,
1174 OID_AUTO, "load", CTLFLAG_RD,
1176 "scaled load average / 100");
1178 SYSCTL_ADD_U64(ctx, n,
1179 OID_AUTO, "latency_trigger", CTLFLAG_RW,
1181 "Latency treshold to trigger callbacks");
1186 cam_iosched_set_latfcn(struct cam_iosched_softc *isc,
1187 cam_iosched_latfcn_t fnp, void *argp)
1189 #ifdef CAM_IOSCHED_DYNAMIC
1196 * Flush outstanding I/O. Consumers of this library don't know all the
1197 * queues we may keep, so this allows all I/O to be flushed in one
1201 cam_iosched_flush(struct cam_iosched_softc *isc, struct devstat *stp, int err)
1203 bioq_flush(&isc->bio_queue, stp, err);
1204 bioq_flush(&isc->trim_queue, stp, err);
1205 #ifdef CAM_IOSCHED_DYNAMIC
1206 if (do_dynamic_iosched)
1207 bioq_flush(&isc->write_queue, stp, err);
1211 #ifdef CAM_IOSCHED_DYNAMIC
1213 cam_iosched_get_write(struct cam_iosched_softc *isc)
1218 * We control the write rate by controlling how many requests we send
1219 * down to the drive at any one time. Fewer requests limits the
1220 * effects of both starvation when the requests take a while and write
1221 * amplification when each request is causing more than one write to
1222 * the NAND media. Limiting the queue depth like this will also limit
1223 * the write throughput and give and reads that want to compete to
1226 bp = bioq_first(&isc->write_queue);
1228 if (iosched_debug > 3)
1229 printf("No writes present in write_queue\n");
1234 * If pending read, prefer that based on current read bias
1237 if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
1240 "Reads present and current_read_bias is %d queued "
1241 "writes %d queued reads %d\n",
1242 isc->current_read_bias, isc->write_stats.queued,
1243 isc->read_stats.queued);
1244 isc->current_read_bias--;
1245 /* We're not limiting writes, per se, just doing reads first */
1250 * See if our current limiter allows this I/O.
1252 if (cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) {
1254 printf("Can't write because limiter says no.\n");
1255 isc->write_stats.state_flags |= IOP_RATE_LIMITED;
1260 * Let's do this: We've passed all the gates and we're a go
1261 * to schedule the I/O in the SIM.
1263 isc->current_read_bias = isc->read_bias;
1264 bioq_remove(&isc->write_queue, bp);
1265 if (bp->bio_cmd == BIO_WRITE) {
1266 isc->write_stats.queued--;
1267 isc->write_stats.total++;
1268 isc->write_stats.pending++;
1270 if (iosched_debug > 9)
1271 printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
1272 isc->write_stats.state_flags &= ~IOP_RATE_LIMITED;
1278 * Put back a trim that you weren't able to actually schedule this time.
1281 cam_iosched_put_back_trim(struct cam_iosched_softc *isc, struct bio *bp)
1283 bioq_insert_head(&isc->trim_queue, bp);
1284 #ifdef CAM_IOSCHED_DYNAMIC
1285 isc->trim_stats.queued++;
1286 isc->trim_stats.total--; /* since we put it back, don't double count */
1287 isc->trim_stats.pending--;
1292 * gets the next trim from the trim queue.
1294 * Assumes we're called with the periph lock held. It removes this
1295 * trim from the queue and the device must explicitly reinsert it
1296 * should the need arise.
1299 cam_iosched_next_trim(struct cam_iosched_softc *isc)
1303 bp = bioq_first(&isc->trim_queue);
1306 bioq_remove(&isc->trim_queue, bp);
1307 #ifdef CAM_IOSCHED_DYNAMIC
1308 isc->trim_stats.queued--;
1309 isc->trim_stats.total++;
1310 isc->trim_stats.pending++;
1316 * gets an available trim from the trim queue, if there's no trim
1317 * already pending. It removes this trim from the queue and the device
1318 * must explicitly reinsert it should the need arise.
1320 * Assumes we're called with the periph lock held.
1323 cam_iosched_get_trim(struct cam_iosched_softc *isc)
1326 if (!cam_iosched_has_more_trim(isc))
1328 #ifdef CAM_IOSCHED_DYNAMIC
1329 if (do_dynamic_iosched) {
1331 * If pending read, prefer that based on current read bias
1332 * setting. The read bias is shared for both writes and
1333 * TRIMs, but on TRIMs the bias is for a combined TRIM
1334 * not a single TRIM request that's come in.
1336 if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
1337 isc->current_read_bias--;
1338 /* We're not limiting TRIMS, per se, just doing reads first */
1342 * We're going to do a trim, so reset the bias.
1344 isc->current_read_bias = isc->read_bias;
1347 return cam_iosched_next_trim(isc);
1351 * Determine what the next bit of work to do is for the periph. The
1352 * default implementation looks to see if we have trims to do, but no
1353 * trims outstanding. If so, we do that. Otherwise we see if we have
1354 * other work. If we do, then we do that. Otherwise why were we called?
1357 cam_iosched_next_bio(struct cam_iosched_softc *isc)
1362 * See if we have a trim that can be scheduled. We can only send one
1363 * at a time down, so this takes that into account.
1365 * XXX newer TRIM commands are queueable. Revisit this when we
1368 if ((bp = cam_iosched_get_trim(isc)) != NULL)
1371 #ifdef CAM_IOSCHED_DYNAMIC
1373 * See if we have any pending writes, and room in the queue for them,
1374 * and if so, those are next.
1376 if (do_dynamic_iosched) {
1377 if ((bp = cam_iosched_get_write(isc)) != NULL)
1383 * next, see if there's other, normal I/O waiting. If so return that.
1385 if ((bp = bioq_first(&isc->bio_queue)) == NULL)
1388 #ifdef CAM_IOSCHED_DYNAMIC
1390 * For the dynamic scheduler, bio_queue is only for reads, so enforce
1391 * the limits here. Enforce only for reads.
1393 if (do_dynamic_iosched) {
1394 if (bp->bio_cmd == BIO_READ &&
1395 cam_iosched_limiter_iop(&isc->read_stats, bp) != 0) {
1396 isc->read_stats.state_flags |= IOP_RATE_LIMITED;
1400 isc->read_stats.state_flags &= ~IOP_RATE_LIMITED;
1402 bioq_remove(&isc->bio_queue, bp);
1403 #ifdef CAM_IOSCHED_DYNAMIC
1404 if (do_dynamic_iosched) {
1405 if (bp->bio_cmd == BIO_READ) {
1406 isc->read_stats.queued--;
1407 isc->read_stats.total++;
1408 isc->read_stats.pending++;
1410 printf("Found bio_cmd = %#x\n", bp->bio_cmd);
1412 if (iosched_debug > 9)
1413 printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
1419 * Driver has been given some work to do by the block layer. Tell the
1420 * scheduler about it and have it queue the work up. The scheduler module
1421 * will then return the currently most useful bit of work later, possibly
1422 * deferring work for various reasons.
1425 cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp)
1429 * Put all trims on the trim queue sorted, since we know
1430 * that the collapsing code requires this. Otherwise put
1431 * the work on the bio queue.
1433 if (bp->bio_cmd == BIO_DELETE) {
1434 bioq_insert_tail(&isc->trim_queue, bp);
1435 #ifdef CAM_IOSCHED_DYNAMIC
1436 isc->trim_stats.in++;
1437 isc->trim_stats.queued++;
1440 #ifdef CAM_IOSCHED_DYNAMIC
1441 else if (do_dynamic_iosched && (bp->bio_cmd != BIO_READ)) {
1442 if (cam_iosched_sort_queue(isc))
1443 bioq_disksort(&isc->write_queue, bp);
1445 bioq_insert_tail(&isc->write_queue, bp);
1446 if (iosched_debug > 9)
1447 printf("Qw : %p %#x\n", bp, bp->bio_cmd);
1448 if (bp->bio_cmd == BIO_WRITE) {
1449 isc->write_stats.in++;
1450 isc->write_stats.queued++;
1455 if (cam_iosched_sort_queue(isc))
1456 bioq_disksort(&isc->bio_queue, bp);
1458 bioq_insert_tail(&isc->bio_queue, bp);
1459 #ifdef CAM_IOSCHED_DYNAMIC
1460 if (iosched_debug > 9)
1461 printf("Qr : %p %#x\n", bp, bp->bio_cmd);
1462 if (bp->bio_cmd == BIO_READ) {
1463 isc->read_stats.in++;
1464 isc->read_stats.queued++;
1465 } else if (bp->bio_cmd == BIO_WRITE) {
1466 isc->write_stats.in++;
1467 isc->write_stats.queued++;
1474 * If we have work, get it scheduled. Called with the periph lock held.
1477 cam_iosched_schedule(struct cam_iosched_softc *isc, struct cam_periph *periph)
1480 if (cam_iosched_has_work(isc))
1481 xpt_schedule(periph, CAM_PRIORITY_NORMAL);
1485 * Complete a trim request. Mark that we no longer have one in flight.
1488 cam_iosched_trim_done(struct cam_iosched_softc *isc)
1491 isc->flags &= ~CAM_IOSCHED_FLAG_TRIM_ACTIVE;
1495 * Complete a bio. Called before we release the ccb with xpt_release_ccb so we
1496 * might use notes in the ccb for statistics.
1499 cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp,
1500 union ccb *done_ccb)
1503 #ifdef CAM_IOSCHED_DYNAMIC
1504 if (!do_dynamic_iosched)
1507 if (iosched_debug > 10)
1508 printf("done: %p %#x\n", bp, bp->bio_cmd);
1509 if (bp->bio_cmd == BIO_WRITE) {
1510 retval = cam_iosched_limiter_iodone(&isc->write_stats, bp);
1511 if ((bp->bio_flags & BIO_ERROR) != 0)
1512 isc->write_stats.errs++;
1513 isc->write_stats.out++;
1514 isc->write_stats.pending--;
1515 } else if (bp->bio_cmd == BIO_READ) {
1516 retval = cam_iosched_limiter_iodone(&isc->read_stats, bp);
1517 if ((bp->bio_flags & BIO_ERROR) != 0)
1518 isc->read_stats.errs++;
1519 isc->read_stats.out++;
1520 isc->read_stats.pending--;
1521 } else if (bp->bio_cmd == BIO_DELETE) {
1522 if ((bp->bio_flags & BIO_ERROR) != 0)
1523 isc->trim_stats.errs++;
1524 isc->trim_stats.out++;
1525 isc->trim_stats.pending--;
1526 } else if (bp->bio_cmd != BIO_FLUSH) {
1528 printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd);
1531 if (!(bp->bio_flags & BIO_ERROR) && done_ccb != NULL) {
1532 sbintime_t sim_latency;
1534 sim_latency = cam_iosched_sbintime_t(done_ccb->ccb_h.qos.periph_data);
1536 cam_iosched_io_metric_update(isc, sim_latency,
1537 bp->bio_cmd, bp->bio_bcount);
1539 * Debugging code: allow callbacks to the periph driver when latency max
1540 * is exceeded. This can be useful for triggering external debugging actions.
1542 if (isc->latfcn && isc->max_lat != 0 && sim_latency > isc->max_lat)
1543 isc->latfcn(isc->latarg, sim_latency, bp);
1551 * Tell the io scheduler that you've pushed a trim down into the sim.
1552 * This also tells the I/O scheduler not to push any more trims down, so
1553 * some periphs do not call it if they can cope with multiple trims in flight.
1556 cam_iosched_submit_trim(struct cam_iosched_softc *isc)
1559 isc->flags |= CAM_IOSCHED_FLAG_TRIM_ACTIVE;
1563 * Change the sorting policy hint for I/O transactions for this device.
1566 cam_iosched_set_sort_queue(struct cam_iosched_softc *isc, int val)
1569 isc->sort_io_queue = val;
1573 cam_iosched_has_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1575 return isc->flags & flags;
1579 cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1581 isc->flags |= flags;
1585 cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1587 isc->flags &= ~flags;
1590 #ifdef CAM_IOSCHED_DYNAMIC
1592 * After the method presented in Jack Crenshaw's 1998 article "Integer
1593 * Square Roots," reprinted at
1594 * http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4219659/Integer-Square-Roots
1595 * and well worth the read. Briefly, we find the power of 4 that's the
1596 * largest smaller than val. We then check each smaller power of 4 to
1597 * see if val is still bigger. The right shifts at each step divide
1598 * the result by 2 which after successive application winds up
1599 * accumulating the right answer. It could also have been accumulated
1600 * using a separate root counter, but this code is smaller and faster
1601 * than that method. This method is also integer size invariant.
1602 * It returns floor(sqrt((float)val)), or the largest integer less than
1603 * or equal to the square root.
1606 isqrt64(uint64_t val)
1609 uint64_t bit = 1ULL << (sizeof(uint64_t) * NBBY - 2);
1612 * Find the largest power of 4 smaller than val.
1618 * Accumulate the answer, one bit at a time (we keep moving
1619 * them over since 2 is the square root of 4 and we test
1620 * powers of 4). We accumulate where we find the bit, but
1621 * the successive shifts land the bit in the right place
1625 if (val >= res + bit) {
1627 res = (res >> 1) + bit;
1636 static sbintime_t latencies[LAT_BUCKETS - 1] = {
1650 SBT_1MS << 13 /* 8.192s */
1654 cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency)
1656 sbintime_t y, deltasq, delta;
1660 * Keep counts for latency. We do it by power of two buckets.
1661 * This helps us spot outlier behavior obscured by averages.
1663 for (i = 0; i < LAT_BUCKETS - 1; i++) {
1664 if (sim_latency < latencies[i]) {
1665 iop->latencies[i]++;
1669 if (i == LAT_BUCKETS - 1)
1670 iop->latencies[i]++; /* Put all > 1024ms values into the last bucket. */
1673 * Classic exponentially decaying average with a tiny alpha
1674 * (2 ^ -alpha_bits). For more info see the NIST statistical
1677 * ema_t = y_t * alpha + ema_t-1 * (1 - alpha) [nist]
1678 * ema_t = y_t * alpha + ema_t-1 - alpha * ema_t-1
1679 * ema_t = alpha * y_t - alpha * ema_t-1 + ema_t-1
1680 * alpha = 1 / (1 << alpha_bits)
1681 * sub e == ema_t-1, b == 1/alpha (== 1 << alpha_bits), d == y_t - ema_t-1
1682 * = y_t/b - e/b + be/b
1683 * = (y_t - e + be) / b
1686 * Since alpha is a power of two, we can compute this w/o any mult or
1689 * Variance can also be computed. Usually, it would be expressed as follows:
1690 * diff_t = y_t - ema_t-1
1691 * emvar_t = (1 - alpha) * (emavar_t-1 + diff_t^2 * alpha)
1692 * = emavar_t-1 - alpha * emavar_t-1 + delta_t^2 * alpha - (delta_t * alpha)^2
1693 * sub b == 1/alpha (== 1 << alpha_bits), e == emavar_t-1, d = delta_t^2
1694 * = e - e/b + dd/b + dd/bb
1695 * = (bbe - be + bdd + dd) / bb
1696 * = (bbe + b(dd-e) + dd) / bb (which is expanded below bb = 1<<(2*alpha_bits))
1699 * XXX possible numeric issues
1700 * o We assume right shifted integers do the right thing, since that's
1701 * implementation defined. You can change the right shifts to / (1LL << alpha).
1702 * o alpha_bits = 9 gives ema ceiling of 23 bits of seconds for ema and 14 bits
1703 * for emvar. This puts a ceiling of 13 bits on alpha since we need a
1704 * few tens of seconds of representation.
1705 * o We mitigate alpha issues by never setting it too high.
1708 delta = (y - iop->ema); /* d */
1709 iop->ema = ((iop->ema << alpha_bits) + delta) >> alpha_bits;
1712 * Were we to naively plow ahead at this point, we wind up with many numerical
1713 * issues making any SD > ~3ms unreliable. So, we shift right by 12. This leaves
1714 * us with microsecond level precision in the input, so the same in the
1715 * output. It means we can't overflow deltasq unless delta > 4k seconds. It
1716 * also means that emvar can be up 46 bits 40 of which are fraction, which
1717 * gives us a way to measure up to ~8s in the SD before the computation goes
1718 * unstable. Even the worst hard disk rarely has > 1s service time in the
1719 * drive. It does mean we have to shift left 12 bits after taking the
1720 * square root to compute the actual standard deviation estimate. This loss of
1721 * precision is preferable to needing int128 types to work. The above numbers
1722 * assume alpha=9. 10 or 11 are ok, but we start to run into issues at 12,
1723 * so 12 or 13 is OK for EMA, EMVAR and SD will be wrong in those cases.
1726 deltasq = delta * delta; /* dd */
1727 iop->emvar = ((iop->emvar << (2 * alpha_bits)) + /* bbe */
1728 ((deltasq - iop->emvar) << alpha_bits) + /* b(dd-e) */
1730 >> (2 * alpha_bits); /* div bb */
1731 iop->sd = (sbintime_t)isqrt64((uint64_t)iop->emvar) << 12;
1735 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
1736 sbintime_t sim_latency, int cmd, size_t size)
1738 /* xxx Do we need to scale based on the size of the I/O ? */
1741 cam_iosched_update(&isc->read_stats, sim_latency);
1744 cam_iosched_update(&isc->write_stats, sim_latency);
1747 cam_iosched_update(&isc->trim_stats, sim_latency);
1755 static int biolen(struct bio_queue_head *bq)
1760 TAILQ_FOREACH(bp, &bq->queue, bio_queue) {
1767 * Show the internal state of the I/O scheduler.
1769 DB_SHOW_COMMAND(iosched, cam_iosched_db_show)
1771 struct cam_iosched_softc *isc;
1774 db_printf("Need addr\n");
1777 isc = (struct cam_iosched_softc *)addr;
1778 db_printf("pending_reads: %d\n", isc->read_stats.pending);
1779 db_printf("min_reads: %d\n", isc->read_stats.min);
1780 db_printf("max_reads: %d\n", isc->read_stats.max);
1781 db_printf("reads: %d\n", isc->read_stats.total);
1782 db_printf("in_reads: %d\n", isc->read_stats.in);
1783 db_printf("out_reads: %d\n", isc->read_stats.out);
1784 db_printf("queued_reads: %d\n", isc->read_stats.queued);
1785 db_printf("Current Q len %d\n", biolen(&isc->bio_queue));
1786 db_printf("pending_writes: %d\n", isc->write_stats.pending);
1787 db_printf("min_writes: %d\n", isc->write_stats.min);
1788 db_printf("max_writes: %d\n", isc->write_stats.max);
1789 db_printf("writes: %d\n", isc->write_stats.total);
1790 db_printf("in_writes: %d\n", isc->write_stats.in);
1791 db_printf("out_writes: %d\n", isc->write_stats.out);
1792 db_printf("queued_writes: %d\n", isc->write_stats.queued);
1793 db_printf("Current Q len %d\n", biolen(&isc->write_queue));
1794 db_printf("pending_trims: %d\n", isc->trim_stats.pending);
1795 db_printf("min_trims: %d\n", isc->trim_stats.min);
1796 db_printf("max_trims: %d\n", isc->trim_stats.max);
1797 db_printf("trims: %d\n", isc->trim_stats.total);
1798 db_printf("in_trims: %d\n", isc->trim_stats.in);
1799 db_printf("out_trims: %d\n", isc->trim_stats.out);
1800 db_printf("queued_trims: %d\n", isc->trim_stats.queued);
1801 db_printf("Current Q len %d\n", biolen(&isc->trim_queue));
1802 db_printf("read_bias: %d\n", isc->read_bias);
1803 db_printf("current_read_bias: %d\n", isc->current_read_bias);
1804 db_printf("Trim active? %s\n",
1805 (isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) ? "yes" : "no");