2 * CAM IO Scheduler Interface
4 * Copyright (c) 2015 Netflix, Inc.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions, and the following disclaimer,
12 * without modification, immediately at the beginning of the file.
13 * 2. The name of the author may not be used to endorse or promote products
14 * derived from this software without specific prior written permission.
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
20 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
37 #include <sys/param.h>
39 #include <sys/systm.h>
40 #include <sys/kernel.h>
43 #include <sys/malloc.h>
44 #include <sys/mutex.h>
46 #include <sys/sysctl.h>
49 #include <cam/cam_ccb.h>
50 #include <cam/cam_periph.h>
51 #include <cam/cam_xpt_periph.h>
52 #include <cam/cam_xpt_internal.h>
53 #include <cam/cam_iosched.h>
57 static MALLOC_DEFINE(M_CAMSCHED, "CAM I/O Scheduler",
58 "CAM I/O Scheduler buffers");
61 * Default I/O scheduler for FreeBSD. This implementation is just a thin-vineer
62 * over the bioq_* interface, with notions of separate calls for normal I/O and
65 * When CAM_IOSCHED_DYNAMIC is defined, the scheduler is enhanced to dynamically
66 * steer the rate of one type of traffic to help other types of traffic (eg
67 * limit writes when read latency deteriorates on SSDs).
70 #ifdef CAM_IOSCHED_DYNAMIC
72 static int do_dynamic_iosched = 1;
73 TUNABLE_INT("kern.cam.do_dynamic_iosched", &do_dynamic_iosched);
74 SYSCTL_INT(_kern_cam, OID_AUTO, do_dynamic_iosched, CTLFLAG_RD,
75 &do_dynamic_iosched, 1,
76 "Enable Dynamic I/O scheduler optimizations.");
79 * For an EMA, with an alpha of alpha, we know
83 * where N is the number of samples that 86% of the current
84 * EMA is derived from.
86 * So we invent[*] alpha_bits:
87 * alpha_bits = -log_2(alpha)
88 * alpha = 2^-alpha_bits
90 * N = 1 + 2^(alpha_bits + 1)
92 * The default 9 gives a 1025 lookback for 86% of the data.
93 * For a brief intro: https://en.wikipedia.org/wiki/Moving_average
95 * [*] Steal from the load average code and many other places.
97 static int alpha_bits = 9;
98 TUNABLE_INT("kern.cam.iosched_alpha_bits", &alpha_bits);
99 SYSCTL_INT(_kern_cam, OID_AUTO, iosched_alpha_bits, CTLFLAG_RW,
101 "Bits in EMA's alpha.");
104 struct cam_iosched_softc;
106 int iosched_debug = 0;
109 none = 0, /* No limits */
110 queue_depth, /* Limit how many ops we queue to SIM */
111 iops, /* Limit # of IOPS to the drive */
112 bandwidth, /* Limit bandwidth to the drive */
116 static const char *cam_iosched_limiter_names[] =
117 { "none", "queue_depth", "iops", "bandwidth" };
120 * Called to initialize the bits of the iop_stats structure relevant to the
121 * limiter. Called just after the limiter is set.
123 typedef int l_init_t(struct iop_stats *);
128 typedef int l_tick_t(struct iop_stats *);
131 * Called to see if the limiter thinks this IOP can be allowed to
132 * proceed. If so, the limiter assumes that the while IOP proceeded
133 * and makes any accounting of it that's needed.
135 typedef int l_iop_t(struct iop_stats *, struct bio *);
138 * Called when an I/O completes so the limiter can updates its
139 * accounting. Pending I/Os may complete in any order (even when
140 * sent to the hardware at the same time), so the limiter may not
141 * make any assumptions other than this I/O has completed. If it
142 * returns 1, then xpt_schedule() needs to be called again.
144 typedef int l_iodone_t(struct iop_stats *, struct bio *);
146 static l_iop_t cam_iosched_qd_iop;
147 static l_iop_t cam_iosched_qd_caniop;
148 static l_iodone_t cam_iosched_qd_iodone;
150 static l_init_t cam_iosched_iops_init;
151 static l_tick_t cam_iosched_iops_tick;
152 static l_iop_t cam_iosched_iops_caniop;
153 static l_iop_t cam_iosched_iops_iop;
155 static l_init_t cam_iosched_bw_init;
156 static l_tick_t cam_iosched_bw_tick;
157 static l_iop_t cam_iosched_bw_caniop;
158 static l_iop_t cam_iosched_bw_iop;
165 l_iodone_t *l_iodone;
177 .l_caniop = cam_iosched_qd_caniop,
178 .l_iop = cam_iosched_qd_iop,
179 .l_iodone= cam_iosched_qd_iodone,
182 .l_init = cam_iosched_iops_init,
183 .l_tick = cam_iosched_iops_tick,
184 .l_caniop = cam_iosched_iops_caniop,
185 .l_iop = cam_iosched_iops_iop,
189 .l_init = cam_iosched_bw_init,
190 .l_tick = cam_iosched_bw_tick,
191 .l_caniop = cam_iosched_bw_caniop,
192 .l_iop = cam_iosched_bw_iop,
199 * sysctl state for this subnode.
201 struct sysctl_ctx_list sysctl_ctx;
202 struct sysctl_oid *sysctl_tree;
205 * Information about the current rate limiters, if any
207 io_limiter limiter; /* How are I/Os being limited */
208 int min; /* Low range of limit */
209 int max; /* High range of limit */
210 int current; /* Current rate limiter */
211 int l_value1; /* per-limiter scratch value 1. */
212 int l_value2; /* per-limiter scratch value 2. */
215 * Debug information about counts of I/Os that have gone through the
218 int pending; /* I/Os pending in the hardware */
219 int queued; /* number currently in the queue */
220 int total; /* Total for all time -- wraps */
221 int in; /* number queued all time -- wraps */
222 int out; /* number completed all time -- wraps */
225 * Statistics on different bits of the process.
227 /* Exp Moving Average, see alpha_bits for more details */
229 sbintime_t emss; /* Exp Moving sum of the squares */
230 sbintime_t sd; /* Last computed sd */
232 uint32_t state_flags;
233 #define IOP_RATE_LIMITED 1u
235 #define LAT_BUCKETS 12 /* < 1ms < 2ms ... 512ms < 1024ms > 1024ms */
236 uint64_t latencies[LAT_BUCKETS];
238 struct cam_iosched_softc *softc;
243 set_max = 0, /* current = max */
244 read_latency, /* Steer read latency by throttling writes */
245 cl_max /* Keep last */
248 static const char *cam_iosched_control_type_names[] =
249 { "set_max", "read_latency" };
251 struct control_loop {
253 * sysctl state for this subnode.
255 struct sysctl_ctx_list sysctl_ctx;
256 struct sysctl_oid *sysctl_tree;
258 sbintime_t next_steer; /* Time of next steer */
259 sbintime_t steer_interval; /* How often do we steer? */
263 control_type type; /* What type of control? */
264 int last_count; /* Last I/O count */
266 struct cam_iosched_softc *softc;
271 struct cam_iosched_softc {
272 struct bio_queue_head bio_queue;
273 struct bio_queue_head trim_queue;
274 /* scheduler flags < 16, user flags >= 16 */
277 #ifdef CAM_IOSCHED_DYNAMIC
278 int read_bias; /* Read bias setting */
279 int current_read_bias; /* Current read bias state */
281 int load; /* EMA of 'load average' of disk / 2^16 */
283 struct bio_queue_head write_queue;
284 struct iop_stats read_stats, write_stats, trim_stats;
285 struct sysctl_ctx_list sysctl_ctx;
286 struct sysctl_oid *sysctl_tree;
288 int quanta; /* Number of quanta per second */
289 struct callout ticker; /* Callout for our quota system */
290 struct cam_periph *periph; /* cam periph associated with this device */
291 uint32_t this_frac; /* Fraction of a second (1024ths) for this tick */
292 sbintime_t last_time; /* Last time we ticked */
293 struct control_loop cl;
297 #ifdef CAM_IOSCHED_DYNAMIC
299 * helper functions to call the limsw functions.
302 cam_iosched_limiter_init(struct iop_stats *ios)
304 int lim = ios->limiter;
306 /* maybe this should be a kassert */
307 if (lim < none || lim >= limiter_max)
310 if (limsw[lim].l_init)
311 return limsw[lim].l_init(ios);
317 cam_iosched_limiter_tick(struct iop_stats *ios)
319 int lim = ios->limiter;
321 /* maybe this should be a kassert */
322 if (lim < none || lim >= limiter_max)
325 if (limsw[lim].l_tick)
326 return limsw[lim].l_tick(ios);
332 cam_iosched_limiter_iop(struct iop_stats *ios, struct bio *bp)
334 int lim = ios->limiter;
336 /* maybe this should be a kassert */
337 if (lim < none || lim >= limiter_max)
340 if (limsw[lim].l_iop)
341 return limsw[lim].l_iop(ios, bp);
347 cam_iosched_limiter_caniop(struct iop_stats *ios, struct bio *bp)
349 int lim = ios->limiter;
351 /* maybe this should be a kassert */
352 if (lim < none || lim >= limiter_max)
355 if (limsw[lim].l_caniop)
356 return limsw[lim].l_caniop(ios, bp);
362 cam_iosched_limiter_iodone(struct iop_stats *ios, struct bio *bp)
364 int lim = ios->limiter;
366 /* maybe this should be a kassert */
367 if (lim < none || lim >= limiter_max)
370 if (limsw[lim].l_iodone)
371 return limsw[lim].l_iodone(ios, bp);
377 * Functions to implement the different kinds of limiters
381 cam_iosched_qd_iop(struct iop_stats *ios, struct bio *bp)
384 if (ios->current <= 0 || ios->pending < ios->current)
391 cam_iosched_qd_caniop(struct iop_stats *ios, struct bio *bp)
394 if (ios->current <= 0 || ios->pending < ios->current)
401 cam_iosched_qd_iodone(struct iop_stats *ios, struct bio *bp)
404 if (ios->current <= 0 || ios->pending != ios->current)
411 cam_iosched_iops_init(struct iop_stats *ios)
414 ios->l_value1 = ios->current / ios->softc->quanta;
415 if (ios->l_value1 <= 0)
422 cam_iosched_iops_tick(struct iop_stats *ios)
425 ios->l_value1 = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
426 if (ios->l_value1 <= 0)
433 cam_iosched_iops_caniop(struct iop_stats *ios, struct bio *bp)
437 * So if we have any more IOPs left, allow it,
440 if (ios->l_value1 <= 0)
446 cam_iosched_iops_iop(struct iop_stats *ios, struct bio *bp)
450 rv = cam_iosched_limiter_caniop(ios, bp);
458 cam_iosched_bw_init(struct iop_stats *ios)
461 /* ios->current is in kB/s, so scale to bytes */
462 ios->l_value1 = ios->current * 1000 / ios->softc->quanta;
468 cam_iosched_bw_tick(struct iop_stats *ios)
473 * If we're in the hole for available quota from
474 * the last time, then add the quantum for this.
475 * If we have any left over from last quantum,
476 * then too bad, that's lost. Also, ios->current
477 * is in kB/s, so scale.
479 * We also allow up to 4 quanta of credits to
480 * accumulate to deal with burstiness. 4 is extremely
483 bw = (int)((ios->current * 1000ull * (uint64_t)ios->softc->this_frac) >> 16);
484 if (ios->l_value1 < bw * 4)
491 cam_iosched_bw_caniop(struct iop_stats *ios, struct bio *bp)
494 * So if we have any more bw quota left, allow it,
495 * otherwise wait. Not, we'll go negative and that's
496 * OK. We'll just get a lettle less next quota.
498 * Note on going negative: that allows us to process
499 * requests in order better, since we won't allow
500 * shorter reads to get around the long one that we
501 * don't have the quota to do just yet. It also prevents
502 * starvation by being a little more permissive about
503 * what we let through this quantum (to prevent the
504 * starvation), at the cost of getting a little less
507 if (ios->l_value1 <= 0)
515 cam_iosched_bw_iop(struct iop_stats *ios, struct bio *bp)
519 rv = cam_iosched_limiter_caniop(ios, bp);
521 ios->l_value1 -= bp->bio_length;
526 static void cam_iosched_cl_maybe_steer(struct control_loop *clp);
529 cam_iosched_ticker(void *arg)
531 struct cam_iosched_softc *isc = arg;
532 sbintime_t now, delta;
535 callout_reset(&isc->ticker, hz / isc->quanta - 1, cam_iosched_ticker, isc);
538 delta = now - isc->last_time;
539 isc->this_frac = (uint32_t)delta >> 16; /* Note: discards seconds -- should be 0 harmless if not */
540 isc->last_time = now;
542 cam_iosched_cl_maybe_steer(&isc->cl);
544 cam_iosched_limiter_tick(&isc->read_stats);
545 cam_iosched_limiter_tick(&isc->write_stats);
546 cam_iosched_limiter_tick(&isc->trim_stats);
548 cam_iosched_schedule(isc, isc->periph);
551 * isc->load is an EMA of the pending I/Os at each tick. The number of
552 * pending I/Os is the sum of the I/Os queued to the hardware, and those
553 * in the software queue that could be queued to the hardware if there
556 * ios_stats.pending is a count of requests in the SIM right now for
557 * each of these types of I/O. So the total pending count is the sum of
558 * these I/Os and the sum of the queued I/Os still in the software queue
559 * for those operations that aren't being rate limited at the moment.
561 * The reason for the rate limiting bit is because those I/Os
562 * aren't part of the software queued load (since we could
563 * give them to hardware, but choose not to).
565 * Note: due to a bug in counting pending TRIM in the device, we
566 * don't include them in this count. We count each BIO_DELETE in
567 * the pending count, but the periph drivers collapse them down
568 * into one TRIM command. That one trim command gets the completion
569 * so the counts get off.
571 pending = isc->read_stats.pending + isc->write_stats.pending /* + isc->trim_stats.pending */;
572 pending += !!(isc->read_stats.state_flags & IOP_RATE_LIMITED) * isc->read_stats.queued +
573 !!(isc->write_stats.state_flags & IOP_RATE_LIMITED) * isc->write_stats.queued /* +
574 !!(isc->trim_stats.state_flags & IOP_RATE_LIMITED) * isc->trim_stats.queued */ ;
576 pending /= isc->periph->path->device->ccbq.total_openings;
578 isc->load = (pending + (isc->load << 13) - isc->load) >> 13; /* see above: 13 -> 16139 / 200/s = ~81s ~1 minute */
585 cam_iosched_cl_init(struct control_loop *clp, struct cam_iosched_softc *isc)
588 clp->next_steer = sbinuptime();
590 clp->steer_interval = SBT_1S * 5; /* Let's start out steering every 5s */
591 clp->lolat = 5 * SBT_1MS;
592 clp->hilat = 15 * SBT_1MS;
593 clp->alpha = 20; /* Alpha == gain. 20 = .2 */
598 cam_iosched_cl_maybe_steer(struct control_loop *clp)
600 struct cam_iosched_softc *isc;
605 now = isc->last_time;
606 if (now < clp->next_steer)
609 clp->next_steer = now + clp->steer_interval;
612 if (isc->write_stats.current != isc->write_stats.max)
613 printf("Steering write from %d kBps to %d kBps\n",
614 isc->write_stats.current, isc->write_stats.max);
615 isc->read_stats.current = isc->read_stats.max;
616 isc->write_stats.current = isc->write_stats.max;
617 isc->trim_stats.current = isc->trim_stats.max;
620 old = isc->write_stats.current;
621 lat = isc->read_stats.ema;
623 * Simple PLL-like engine. Since we're steering to a range for
624 * the SP (set point) that makes things a little more
625 * complicated. In addition, we're not directly controlling our
626 * PV (process variable), the read latency, but instead are
627 * manipulating the write bandwidth limit for our MV
628 * (manipulation variable), analysis of this code gets a bit
629 * messy. Also, the MV is a very noisy control surface for read
630 * latency since it is affected by many hidden processes inside
631 * the device which change how responsive read latency will be
632 * in reaction to changes in write bandwidth. Unlike the classic
633 * boiler control PLL. this may result in over-steering while
634 * the SSD takes its time to react to the new, lower load. This
635 * is why we use a relatively low alpha of between .1 and .25 to
636 * compensate for this effect. At .1, it takes ~22 steering
637 * intervals to back off by a factor of 10. At .2 it only takes
638 * ~10. At .25 it only takes ~8. However some preliminary data
639 * from the SSD drives suggests a reasponse time in 10's of
640 * seconds before latency drops regardless of the new write
641 * rate. Careful observation will be reqiured to tune this
644 * Also, when there's no read traffic, we jack up the write
645 * limit too regardless of the last read latency. 10 is
646 * somewhat arbitrary.
648 if (lat < clp->lolat || isc->read_stats.total - clp->last_count < 10)
649 isc->write_stats.current = isc->write_stats.current *
650 (100 + clp->alpha) / 100; /* Scale up */
651 else if (lat > clp->hilat)
652 isc->write_stats.current = isc->write_stats.current *
653 (100 - clp->alpha) / 100; /* Scale down */
654 clp->last_count = isc->read_stats.total;
657 * Even if we don't steer, per se, enforce the min/max limits as
658 * those may have changed.
660 if (isc->write_stats.current < isc->write_stats.min)
661 isc->write_stats.current = isc->write_stats.min;
662 if (isc->write_stats.current > isc->write_stats.max)
663 isc->write_stats.current = isc->write_stats.max;
664 if (old != isc->write_stats.current && iosched_debug)
665 printf("Steering write from %d kBps to %d kBps due to latency of %jdus\n",
666 old, isc->write_stats.current,
667 (uintmax_t)((uint64_t)1000000 * (uint32_t)lat) >> 32);
675 /* Trim or similar currently pending completion */
676 #define CAM_IOSCHED_FLAG_TRIM_ACTIVE (1ul << 0)
677 /* Callout active, and needs to be torn down */
678 #define CAM_IOSCHED_FLAG_CALLOUT_ACTIVE (1ul << 1)
680 /* Periph drivers set these flags to indicate work */
681 #define CAM_IOSCHED_FLAG_WORK_FLAGS ((0xffffu) << 16)
683 #ifdef CAM_IOSCHED_DYNAMIC
685 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
686 sbintime_t sim_latency, int cmd, size_t size);
690 cam_iosched_has_flagged_work(struct cam_iosched_softc *isc)
692 return !!(isc->flags & CAM_IOSCHED_FLAG_WORK_FLAGS);
696 cam_iosched_has_io(struct cam_iosched_softc *isc)
698 #ifdef CAM_IOSCHED_DYNAMIC
699 if (do_dynamic_iosched) {
700 struct bio *rbp = bioq_first(&isc->bio_queue);
701 struct bio *wbp = bioq_first(&isc->write_queue);
702 int can_write = wbp != NULL &&
703 cam_iosched_limiter_caniop(&isc->write_stats, wbp) == 0;
704 int can_read = rbp != NULL &&
705 cam_iosched_limiter_caniop(&isc->read_stats, rbp) == 0;
706 if (iosched_debug > 2) {
707 printf("can write %d: pending_writes %d max_writes %d\n", can_write, isc->write_stats.pending, isc->write_stats.max);
708 printf("can read %d: read_stats.pending %d max_reads %d\n", can_read, isc->read_stats.pending, isc->read_stats.max);
709 printf("Queued reads %d writes %d\n", isc->read_stats.queued, isc->write_stats.queued);
711 return can_read || can_write;
714 return bioq_first(&isc->bio_queue) != NULL;
718 cam_iosched_has_more_trim(struct cam_iosched_softc *isc)
720 return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) &&
721 bioq_first(&isc->trim_queue);
724 #define cam_iosched_sort_queue(isc) ((isc)->sort_io_queue >= 0 ? \
725 (isc)->sort_io_queue : cam_sort_io_queues)
729 cam_iosched_has_work(struct cam_iosched_softc *isc)
731 #ifdef CAM_IOSCHED_DYNAMIC
732 if (iosched_debug > 2)
733 printf("has work: %d %d %d\n", cam_iosched_has_io(isc),
734 cam_iosched_has_more_trim(isc),
735 cam_iosched_has_flagged_work(isc));
738 return cam_iosched_has_io(isc) ||
739 cam_iosched_has_more_trim(isc) ||
740 cam_iosched_has_flagged_work(isc);
743 #ifdef CAM_IOSCHED_DYNAMIC
745 cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios)
749 cam_iosched_limiter_init(ios);
764 cam_iosched_limiter_sysctl(SYSCTL_HANDLER_ARGS)
767 struct iop_stats *ios;
768 struct cam_iosched_softc *isc;
774 value = ios->limiter;
775 if (value < none || value >= limiter_max)
778 p = cam_iosched_limiter_names[value];
780 strlcpy(buf, p, sizeof(buf));
781 error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
782 if (error != 0 || req->newptr == NULL)
785 cam_periph_lock(isc->periph);
787 for (i = none; i < limiter_max; i++) {
788 if (strcmp(buf, cam_iosched_limiter_names[i]) != 0)
791 error = cam_iosched_limiter_init(ios);
793 ios->limiter = value;
794 cam_periph_unlock(isc->periph);
797 /* Note: disk load averate requires ticker to be always running */
798 callout_reset(&isc->ticker, hz / isc->quanta - 1, cam_iosched_ticker, isc);
799 isc->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
801 cam_periph_unlock(isc->periph);
805 cam_periph_unlock(isc->periph);
810 cam_iosched_control_type_sysctl(SYSCTL_HANDLER_ARGS)
813 struct control_loop *clp;
814 struct cam_iosched_softc *isc;
821 if (value < none || value >= cl_max)
824 p = cam_iosched_control_type_names[value];
826 strlcpy(buf, p, sizeof(buf));
827 error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
828 if (error != 0 || req->newptr == NULL)
831 for (i = set_max; i < cl_max; i++) {
832 if (strcmp(buf, cam_iosched_control_type_names[i]) != 0)
834 cam_periph_lock(isc->periph);
836 cam_periph_unlock(isc->periph);
844 cam_iosched_sbintime_sysctl(SYSCTL_HANDLER_ARGS)
851 value = *(sbintime_t *)arg1;
852 us = (uint64_t)value / SBT_1US;
853 snprintf(buf, sizeof(buf), "%ju", (intmax_t)us);
854 error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
855 if (error != 0 || req->newptr == NULL)
857 us = strtoul(buf, NULL, 10);
860 *(sbintime_t *)arg1 = us * SBT_1US;
865 cam_iosched_sysctl_latencies(SYSCTL_HANDLER_ARGS)
872 sbuf_new_for_sysctl(&sb, NULL, LAT_BUCKETS * 16, req);
874 for (i = 0; i < LAT_BUCKETS - 1; i++)
875 sbuf_printf(&sb, "%jd,", (intmax_t)latencies[i]);
876 sbuf_printf(&sb, "%jd", (intmax_t)latencies[LAT_BUCKETS - 1]);
877 error = sbuf_finish(&sb);
884 cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stats *ios, char *name)
886 struct sysctl_oid_list *n;
887 struct sysctl_ctx_list *ctx;
889 ios->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
890 SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, name,
891 CTLFLAG_RD, 0, name);
892 n = SYSCTL_CHILDREN(ios->sysctl_tree);
893 ctx = &ios->sysctl_ctx;
895 SYSCTL_ADD_UQUAD(ctx, n,
896 OID_AUTO, "ema", CTLFLAG_RD,
898 "Fast Exponentially Weighted Moving Average");
899 SYSCTL_ADD_UQUAD(ctx, n,
900 OID_AUTO, "emss", CTLFLAG_RD,
902 "Fast Exponentially Weighted Moving Sum of Squares (maybe wrong)");
903 SYSCTL_ADD_UQUAD(ctx, n,
904 OID_AUTO, "sd", CTLFLAG_RD,
906 "Estimated SD for fast ema (may be wrong)");
908 SYSCTL_ADD_INT(ctx, n,
909 OID_AUTO, "pending", CTLFLAG_RD,
911 "Instantaneous # of pending transactions");
912 SYSCTL_ADD_INT(ctx, n,
913 OID_AUTO, "count", CTLFLAG_RD,
915 "# of transactions submitted to hardware");
916 SYSCTL_ADD_INT(ctx, n,
917 OID_AUTO, "queued", CTLFLAG_RD,
919 "# of transactions in the queue");
920 SYSCTL_ADD_INT(ctx, n,
921 OID_AUTO, "in", CTLFLAG_RD,
923 "# of transactions queued to driver");
924 SYSCTL_ADD_INT(ctx, n,
925 OID_AUTO, "out", CTLFLAG_RD,
927 "# of transactions completed");
929 SYSCTL_ADD_PROC(ctx, n,
930 OID_AUTO, "limiter", CTLTYPE_STRING | CTLFLAG_RW,
931 ios, 0, cam_iosched_limiter_sysctl, "A",
932 "Current limiting type.");
933 SYSCTL_ADD_INT(ctx, n,
934 OID_AUTO, "min", CTLFLAG_RW,
937 SYSCTL_ADD_INT(ctx, n,
938 OID_AUTO, "max", CTLFLAG_RW,
941 SYSCTL_ADD_INT(ctx, n,
942 OID_AUTO, "current", CTLFLAG_RW,
946 SYSCTL_ADD_PROC(ctx, n,
947 OID_AUTO, "latencies", CTLTYPE_STRING | CTLFLAG_RD,
949 cam_iosched_sysctl_latencies, "A",
950 "Array of power of 2 latency from 1ms to 1.024s");
954 cam_iosched_iop_stats_fini(struct iop_stats *ios)
956 if (ios->sysctl_tree)
957 if (sysctl_ctx_free(&ios->sysctl_ctx) != 0)
958 printf("can't remove iosched sysctl stats context\n");
962 cam_iosched_cl_sysctl_init(struct cam_iosched_softc *isc)
964 struct sysctl_oid_list *n;
965 struct sysctl_ctx_list *ctx;
966 struct control_loop *clp;
969 clp->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
970 SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, "control",
971 CTLFLAG_RD, 0, "Control loop info");
972 n = SYSCTL_CHILDREN(clp->sysctl_tree);
973 ctx = &clp->sysctl_ctx;
975 SYSCTL_ADD_PROC(ctx, n,
976 OID_AUTO, "type", CTLTYPE_STRING | CTLFLAG_RW,
977 clp, 0, cam_iosched_control_type_sysctl, "A",
978 "Control loop algorithm");
979 SYSCTL_ADD_PROC(ctx, n,
980 OID_AUTO, "steer_interval", CTLTYPE_STRING | CTLFLAG_RW,
981 &clp->steer_interval, 0, cam_iosched_sbintime_sysctl, "A",
982 "How often to steer (in us)");
983 SYSCTL_ADD_PROC(ctx, n,
984 OID_AUTO, "lolat", CTLTYPE_STRING | CTLFLAG_RW,
985 &clp->lolat, 0, cam_iosched_sbintime_sysctl, "A",
986 "Low water mark for Latency (in us)");
987 SYSCTL_ADD_PROC(ctx, n,
988 OID_AUTO, "hilat", CTLTYPE_STRING | CTLFLAG_RW,
989 &clp->hilat, 0, cam_iosched_sbintime_sysctl, "A",
990 "Hi water mark for Latency (in us)");
991 SYSCTL_ADD_INT(ctx, n,
992 OID_AUTO, "alpha", CTLFLAG_RW,
994 "Alpha for PLL (x100) aka gain");
998 cam_iosched_cl_sysctl_fini(struct control_loop *clp)
1000 if (clp->sysctl_tree)
1001 if (sysctl_ctx_free(&clp->sysctl_ctx) != 0)
1002 printf("can't remove iosched sysctl control loop context\n");
1007 * Allocate the iosched structure. This also insulates callers from knowing
1008 * sizeof struct cam_iosched_softc.
1011 cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph)
1014 *iscp = malloc(sizeof(**iscp), M_CAMSCHED, M_NOWAIT | M_ZERO);
1017 #ifdef CAM_IOSCHED_DYNAMIC
1019 printf("CAM IOSCHEDULER Allocating entry at %p\n", *iscp);
1021 (*iscp)->sort_io_queue = -1;
1022 bioq_init(&(*iscp)->bio_queue);
1023 bioq_init(&(*iscp)->trim_queue);
1024 #ifdef CAM_IOSCHED_DYNAMIC
1025 if (do_dynamic_iosched) {
1026 bioq_init(&(*iscp)->write_queue);
1027 (*iscp)->read_bias = 100;
1028 (*iscp)->current_read_bias = 100;
1029 (*iscp)->quanta = 200;
1030 cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats);
1031 cam_iosched_iop_stats_init(*iscp, &(*iscp)->write_stats);
1032 cam_iosched_iop_stats_init(*iscp, &(*iscp)->trim_stats);
1033 (*iscp)->trim_stats.max = 1; /* Trims are special: one at a time for now */
1034 (*iscp)->last_time = sbinuptime();
1035 callout_init_mtx(&(*iscp)->ticker, cam_periph_mtx(periph), 0);
1036 (*iscp)->periph = periph;
1037 cam_iosched_cl_init(&(*iscp)->cl, *iscp);
1038 callout_reset(&(*iscp)->ticker, hz / (*iscp)->quanta - 1, cam_iosched_ticker, *iscp);
1039 (*iscp)->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
1047 * Reclaim all used resources. This assumes that other folks have
1048 * drained the requests in the hardware. Maybe an unwise assumption.
1051 cam_iosched_fini(struct cam_iosched_softc *isc)
1054 cam_iosched_flush(isc, NULL, ENXIO);
1055 #ifdef CAM_IOSCHED_DYNAMIC
1056 cam_iosched_iop_stats_fini(&isc->read_stats);
1057 cam_iosched_iop_stats_fini(&isc->write_stats);
1058 cam_iosched_iop_stats_fini(&isc->trim_stats);
1059 cam_iosched_cl_sysctl_fini(&isc->cl);
1060 if (isc->sysctl_tree)
1061 if (sysctl_ctx_free(&isc->sysctl_ctx) != 0)
1062 printf("can't remove iosched sysctl stats context\n");
1063 if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) {
1064 callout_drain(&isc->ticker);
1065 isc->flags &= ~ CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
1068 free(isc, M_CAMSCHED);
1073 * After we're sure we're attaching a device, go ahead and add
1074 * hooks for any sysctl we may wish to honor.
1076 void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
1077 struct sysctl_ctx_list *ctx, struct sysctl_oid *node)
1079 #ifdef CAM_IOSCHED_DYNAMIC
1080 struct sysctl_oid_list *n;
1083 SYSCTL_ADD_INT(ctx, SYSCTL_CHILDREN(node),
1084 OID_AUTO, "sort_io_queue", CTLFLAG_RW | CTLFLAG_MPSAFE,
1085 &isc->sort_io_queue, 0,
1086 "Sort IO queue to try and optimise disk access patterns");
1088 #ifdef CAM_IOSCHED_DYNAMIC
1089 if (!do_dynamic_iosched)
1092 isc->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
1093 SYSCTL_CHILDREN(node), OID_AUTO, "iosched",
1094 CTLFLAG_RD, 0, "I/O scheduler statistics");
1095 n = SYSCTL_CHILDREN(isc->sysctl_tree);
1096 ctx = &isc->sysctl_ctx;
1098 cam_iosched_iop_stats_sysctl_init(isc, &isc->read_stats, "read");
1099 cam_iosched_iop_stats_sysctl_init(isc, &isc->write_stats, "write");
1100 cam_iosched_iop_stats_sysctl_init(isc, &isc->trim_stats, "trim");
1101 cam_iosched_cl_sysctl_init(isc);
1103 SYSCTL_ADD_INT(ctx, n,
1104 OID_AUTO, "read_bias", CTLFLAG_RW,
1105 &isc->read_bias, 100,
1106 "How biased towards read should we be independent of limits");
1108 SYSCTL_ADD_INT(ctx, n,
1109 OID_AUTO, "quanta", CTLFLAG_RW,
1111 "How many quanta per second do we slice the I/O up into");
1113 SYSCTL_ADD_INT(ctx, n,
1114 OID_AUTO, "total_ticks", CTLFLAG_RD,
1115 &isc->total_ticks, 0,
1116 "Total number of ticks we've done");
1118 SYSCTL_ADD_INT(ctx, n,
1119 OID_AUTO, "load", CTLFLAG_RD,
1121 "scaled load average / 100");
1126 * Flush outstanding I/O. Consumers of this library don't know all the
1127 * queues we may keep, so this allows all I/O to be flushed in one
1131 cam_iosched_flush(struct cam_iosched_softc *isc, struct devstat *stp, int err)
1133 bioq_flush(&isc->bio_queue, stp, err);
1134 bioq_flush(&isc->trim_queue, stp, err);
1135 #ifdef CAM_IOSCHED_DYNAMIC
1136 if (do_dynamic_iosched)
1137 bioq_flush(&isc->write_queue, stp, err);
1141 #ifdef CAM_IOSCHED_DYNAMIC
1143 cam_iosched_get_write(struct cam_iosched_softc *isc)
1148 * We control the write rate by controlling how many requests we send
1149 * down to the drive at any one time. Fewer requests limits the
1150 * effects of both starvation when the requests take a while and write
1151 * amplification when each request is causing more than one write to
1152 * the NAND media. Limiting the queue depth like this will also limit
1153 * the write throughput and give and reads that want to compete to
1156 bp = bioq_first(&isc->write_queue);
1158 if (iosched_debug > 3)
1159 printf("No writes present in write_queue\n");
1164 * If pending read, prefer that based on current read bias
1167 if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
1169 printf("Reads present and current_read_bias is %d queued writes %d queued reads %d\n", isc->current_read_bias, isc->write_stats.queued, isc->read_stats.queued);
1170 isc->current_read_bias--;
1171 /* We're not limiting writes, per se, just doing reads first */
1176 * See if our current limiter allows this I/O.
1178 if (cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) {
1180 printf("Can't write because limiter says no.\n");
1181 isc->write_stats.state_flags |= IOP_RATE_LIMITED;
1186 * Let's do this: We've passed all the gates and we're a go
1187 * to schedule the I/O in the SIM.
1189 isc->current_read_bias = isc->read_bias;
1190 bioq_remove(&isc->write_queue, bp);
1191 if (bp->bio_cmd == BIO_WRITE) {
1192 isc->write_stats.queued--;
1193 isc->write_stats.total++;
1194 isc->write_stats.pending++;
1196 if (iosched_debug > 9)
1197 printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
1198 isc->write_stats.state_flags &= ~IOP_RATE_LIMITED;
1204 * Put back a trim that you weren't able to actually schedule this time.
1207 cam_iosched_put_back_trim(struct cam_iosched_softc *isc, struct bio *bp)
1209 bioq_insert_head(&isc->trim_queue, bp);
1210 #ifdef CAM_IOSCHED_DYNAMIC
1211 isc->trim_stats.queued++;
1212 isc->trim_stats.total--; /* since we put it back, don't double count */
1213 isc->trim_stats.pending--;
1218 * gets the next trim from the trim queue.
1220 * Assumes we're called with the periph lock held. It removes this
1221 * trim from the queue and the device must explicitly reinstert it
1222 * should the need arise.
1225 cam_iosched_next_trim(struct cam_iosched_softc *isc)
1229 bp = bioq_first(&isc->trim_queue);
1232 bioq_remove(&isc->trim_queue, bp);
1233 #ifdef CAM_IOSCHED_DYNAMIC
1234 isc->trim_stats.queued--;
1235 isc->trim_stats.total++;
1236 isc->trim_stats.pending++;
1242 * gets the an available trim from the trim queue, if there's no trim
1243 * already pending. It removes this trim from the queue and the device
1244 * must explicitly reinstert it should the need arise.
1246 * Assumes we're called with the periph lock held.
1249 cam_iosched_get_trim(struct cam_iosched_softc *isc)
1252 if (!cam_iosched_has_more_trim(isc))
1255 return cam_iosched_next_trim(isc);
1259 * Determine what the next bit of work to do is for the periph. The
1260 * default implementation looks to see if we have trims to do, but no
1261 * trims outstanding. If so, we do that. Otherwise we see if we have
1262 * other work. If we do, then we do that. Otherwise why were we called?
1265 cam_iosched_next_bio(struct cam_iosched_softc *isc)
1270 * See if we have a trim that can be scheduled. We can only send one
1271 * at a time down, so this takes that into account.
1273 * XXX newer TRIM commands are queueable. Revisit this when we
1276 if ((bp = cam_iosched_get_trim(isc)) != NULL)
1279 #ifdef CAM_IOSCHED_DYNAMIC
1281 * See if we have any pending writes, and room in the queue for them,
1282 * and if so, those are next.
1284 if (do_dynamic_iosched) {
1285 if ((bp = cam_iosched_get_write(isc)) != NULL)
1291 * next, see if there's other, normal I/O waiting. If so return that.
1293 if ((bp = bioq_first(&isc->bio_queue)) == NULL)
1296 #ifdef CAM_IOSCHED_DYNAMIC
1298 * For the dynamic scheduler, bio_queue is only for reads, so enforce
1299 * the limits here. Enforce only for reads.
1301 if (do_dynamic_iosched) {
1302 if (bp->bio_cmd == BIO_READ &&
1303 cam_iosched_limiter_iop(&isc->read_stats, bp) != 0) {
1304 isc->read_stats.state_flags |= IOP_RATE_LIMITED;
1308 isc->read_stats.state_flags &= ~IOP_RATE_LIMITED;
1310 bioq_remove(&isc->bio_queue, bp);
1311 #ifdef CAM_IOSCHED_DYNAMIC
1312 if (do_dynamic_iosched) {
1313 if (bp->bio_cmd == BIO_READ) {
1314 isc->read_stats.queued--;
1315 isc->read_stats.total++;
1316 isc->read_stats.pending++;
1318 printf("Found bio_cmd = %#x\n", bp->bio_cmd);
1320 if (iosched_debug > 9)
1321 printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
1327 * Driver has been given some work to do by the block layer. Tell the
1328 * scheduler about it and have it queue the work up. The scheduler module
1329 * will then return the currently most useful bit of work later, possibly
1330 * deferring work for various reasons.
1333 cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp)
1337 * Put all trims on the trim queue sorted, since we know
1338 * that the collapsing code requires this. Otherwise put
1339 * the work on the bio queue.
1341 if (bp->bio_cmd == BIO_DELETE) {
1342 bioq_disksort(&isc->trim_queue, bp);
1343 #ifdef CAM_IOSCHED_DYNAMIC
1344 isc->trim_stats.in++;
1345 isc->trim_stats.queued++;
1348 #ifdef CAM_IOSCHED_DYNAMIC
1349 else if (do_dynamic_iosched &&
1350 (bp->bio_cmd == BIO_WRITE || bp->bio_cmd == BIO_FLUSH)) {
1351 if (cam_iosched_sort_queue(isc))
1352 bioq_disksort(&isc->write_queue, bp);
1354 bioq_insert_tail(&isc->write_queue, bp);
1355 if (iosched_debug > 9)
1356 printf("Qw : %p %#x\n", bp, bp->bio_cmd);
1357 if (bp->bio_cmd == BIO_WRITE) {
1358 isc->write_stats.in++;
1359 isc->write_stats.queued++;
1364 if (cam_iosched_sort_queue(isc))
1365 bioq_disksort(&isc->bio_queue, bp);
1367 bioq_insert_tail(&isc->bio_queue, bp);
1368 #ifdef CAM_IOSCHED_DYNAMIC
1369 if (iosched_debug > 9)
1370 printf("Qr : %p %#x\n", bp, bp->bio_cmd);
1371 if (bp->bio_cmd == BIO_READ) {
1372 isc->read_stats.in++;
1373 isc->read_stats.queued++;
1374 } else if (bp->bio_cmd == BIO_WRITE) {
1375 isc->write_stats.in++;
1376 isc->write_stats.queued++;
1383 * If we have work, get it scheduled. Called with the periph lock held.
1386 cam_iosched_schedule(struct cam_iosched_softc *isc, struct cam_periph *periph)
1389 if (cam_iosched_has_work(isc))
1390 xpt_schedule(periph, CAM_PRIORITY_NORMAL);
1394 * Complete a trim request
1397 cam_iosched_trim_done(struct cam_iosched_softc *isc)
1400 isc->flags &= ~CAM_IOSCHED_FLAG_TRIM_ACTIVE;
1404 * Complete a bio. Called before we release the ccb with xpt_release_ccb so we
1405 * might use notes in the ccb for statistics.
1408 cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp,
1409 union ccb *done_ccb)
1412 #ifdef CAM_IOSCHED_DYNAMIC
1413 if (!do_dynamic_iosched)
1416 if (iosched_debug > 10)
1417 printf("done: %p %#x\n", bp, bp->bio_cmd);
1418 if (bp->bio_cmd == BIO_WRITE) {
1419 retval = cam_iosched_limiter_iodone(&isc->write_stats, bp);
1420 isc->write_stats.out++;
1421 isc->write_stats.pending--;
1422 } else if (bp->bio_cmd == BIO_READ) {
1423 retval = cam_iosched_limiter_iodone(&isc->read_stats, bp);
1424 isc->read_stats.out++;
1425 isc->read_stats.pending--;
1426 } else if (bp->bio_cmd == BIO_DELETE) {
1427 isc->trim_stats.out++;
1428 isc->trim_stats.pending--;
1429 } else if (bp->bio_cmd != BIO_FLUSH) {
1431 printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd);
1434 if (!(bp->bio_flags & BIO_ERROR))
1435 cam_iosched_io_metric_update(isc, done_ccb->ccb_h.qos.sim_data,
1436 bp->bio_cmd, bp->bio_bcount);
1442 * Tell the io scheduler that you've pushed a trim down into the sim.
1443 * xxx better place for this?
1446 cam_iosched_submit_trim(struct cam_iosched_softc *isc)
1449 isc->flags |= CAM_IOSCHED_FLAG_TRIM_ACTIVE;
1453 * Change the sorting policy hint for I/O transactions for this device.
1456 cam_iosched_set_sort_queue(struct cam_iosched_softc *isc, int val)
1459 isc->sort_io_queue = val;
1463 cam_iosched_has_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1465 return isc->flags & flags;
1469 cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1471 isc->flags |= flags;
1475 cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1477 isc->flags &= ~flags;
1480 #ifdef CAM_IOSCHED_DYNAMIC
1482 * After the method presented in Jack Crenshaw's 1998 article "Integer
1483 * Suqare Roots," reprinted at
1484 * http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4219659/Integer-Square-Roots
1485 * and well worth the read. Briefly, we find the power of 4 that's the
1486 * largest smaller than val. We then check each smaller power of 4 to
1487 * see if val is still bigger. The right shifts at each step divide
1488 * the result by 2 which after successive application winds up
1489 * accumulating the right answer. It could also have been accumulated
1490 * using a separate root counter, but this code is smaller and faster
1491 * than that method. This method is also integer size invariant.
1492 * It returns floor(sqrt((float)val)), or the larget integer less than
1493 * or equal to the square root.
1496 isqrt64(uint64_t val)
1499 uint64_t bit = 1ULL << (sizeof(uint64_t) * NBBY - 2);
1502 * Find the largest power of 4 smaller than val.
1508 * Accumulate the answer, one bit at a time (we keep moving
1509 * them over since 2 is the square root of 4 and we test
1510 * powers of 4). We accumulate where we find the bit, but
1511 * the successive shifts land the bit in the right place
1515 if (val >= res + bit) {
1517 res = (res >> 1) + bit;
1527 * a and b are 32.32 fixed point stored in a 64-bit word.
1528 * Let al and bl be the .32 part of a and b.
1529 * Let ah and bh be the 32 part of a and b.
1530 * R is the radix and is 1 << 32
1533 * (ah + al / R) * (bh + bl / R)
1534 * ah * bh + (al * bh + ah * bl) / R + al * bl / R^2
1536 * After multiplicaiton, we have to renormalize by multiply by
1537 * R, so we wind up with
1538 * ah * bh * R + al * bh + ah * bl + al * bl / R
1539 * which turns out to be a very nice way to compute this value
1540 * so long as ah and bh are < 65536 there's no loss of high bits
1541 * and the low order bits are below the threshold of caring for
1545 mul(uint64_t a, uint64_t b)
1547 uint64_t al, ah, bl, bh;
1548 al = a & 0xffffffff;
1550 bl = b & 0xffffffff;
1552 return ((ah * bh) << 32) + al * bh + ah * bl + ((al * bl) >> 32);
1555 static sbintime_t latencies[] = {
1570 cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency)
1577 * Keep counts for latency. We do it by power of two buckets.
1578 * This helps us spot outlier behavior obscured by averages.
1580 for (i = 0; i < LAT_BUCKETS - 1; i++) {
1581 if (sim_latency < latencies[i]) {
1582 iop->latencies[i]++;
1586 if (i == LAT_BUCKETS - 1)
1587 iop->latencies[i]++; /* Put all > 1024ms values into the last bucket. */
1590 * Classic expoentially decaying average with a tiny alpha
1591 * (2 ^ -alpha_bits). For more info see the NIST statistical
1594 * ema_t = y_t * alpha + ema_t-1 * (1 - alpha)
1595 * alpha = 1 / (1 << alpha_bits)
1597 * Since alpha is a power of two, we can compute this w/o any mult or
1601 iop->ema = (y + (iop->ema << alpha_bits) - iop->ema) >> alpha_bits;
1604 iop->emss = (yy + (iop->emss << alpha_bits) - iop->emss) >> alpha_bits;
1608 * s_2 = sum of data * data
1609 * ema ~ mean (or s_1 / N)
1612 * sd = sqrt((N * s_2 - s_1 ^ 2) / (N * (N - 1)))
1613 * sd = sqrt((N * s_2 / N * (N - 1)) - (s_1 ^ 2 / (N * (N - 1))))
1616 * alpha < 1 / 16 (typically much less)
1617 * N > 31 --> N large so N * (N - 1) is approx N * N
1619 * substituting and rearranging:
1620 * sd ~ sqrt(s_2 / N - (s_1 / N) ^ 2)
1621 * ~ sqrt(emss - ema ^ 2);
1622 * which is the formula used here to get a decent estimate of sd which
1623 * we use to detect outliers. Note that when first starting up, it
1624 * takes a while for emss sum of squares estimator to converge on a
1625 * good value. during this time, it can be less than ema^2. We
1626 * compute a sd of 0 in that case, and ignore outliers.
1628 var = iop->emss - mul(iop->ema, iop->ema);
1629 iop->sd = (int64_t)var < 0 ? 0 : isqrt64(var);
1633 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
1634 sbintime_t sim_latency, int cmd, size_t size)
1636 /* xxx Do we need to scale based on the size of the I/O ? */
1639 cam_iosched_update(&isc->read_stats, sim_latency);
1642 cam_iosched_update(&isc->write_stats, sim_latency);
1645 cam_iosched_update(&isc->trim_stats, sim_latency);
1653 static int biolen(struct bio_queue_head *bq)
1658 TAILQ_FOREACH(bp, &bq->queue, bio_queue) {
1665 * Show the internal state of the I/O scheduler.
1667 DB_SHOW_COMMAND(iosched, cam_iosched_db_show)
1669 struct cam_iosched_softc *isc;
1672 db_printf("Need addr\n");
1675 isc = (struct cam_iosched_softc *)addr;
1676 db_printf("pending_reads: %d\n", isc->read_stats.pending);
1677 db_printf("min_reads: %d\n", isc->read_stats.min);
1678 db_printf("max_reads: %d\n", isc->read_stats.max);
1679 db_printf("reads: %d\n", isc->read_stats.total);
1680 db_printf("in_reads: %d\n", isc->read_stats.in);
1681 db_printf("out_reads: %d\n", isc->read_stats.out);
1682 db_printf("queued_reads: %d\n", isc->read_stats.queued);
1683 db_printf("Current Q len %d\n", biolen(&isc->bio_queue));
1684 db_printf("pending_writes: %d\n", isc->write_stats.pending);
1685 db_printf("min_writes: %d\n", isc->write_stats.min);
1686 db_printf("max_writes: %d\n", isc->write_stats.max);
1687 db_printf("writes: %d\n", isc->write_stats.total);
1688 db_printf("in_writes: %d\n", isc->write_stats.in);
1689 db_printf("out_writes: %d\n", isc->write_stats.out);
1690 db_printf("queued_writes: %d\n", isc->write_stats.queued);
1691 db_printf("Current Q len %d\n", biolen(&isc->write_queue));
1692 db_printf("pending_trims: %d\n", isc->trim_stats.pending);
1693 db_printf("min_trims: %d\n", isc->trim_stats.min);
1694 db_printf("max_trims: %d\n", isc->trim_stats.max);
1695 db_printf("trims: %d\n", isc->trim_stats.total);
1696 db_printf("in_trims: %d\n", isc->trim_stats.in);
1697 db_printf("out_trims: %d\n", isc->trim_stats.out);
1698 db_printf("queued_trims: %d\n", isc->trim_stats.queued);
1699 db_printf("Current Q len %d\n", biolen(&isc->trim_queue));
1700 db_printf("read_bias: %d\n", isc->read_bias);
1701 db_printf("current_read_bias: %d\n", isc->current_read_bias);
1702 db_printf("Trim active? %s\n",
1703 (isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) ? "yes" : "no");