/*- * Copyright (c) 2009-2010 Fabio Checconi * Copyright (c) 2009-2010 Luigi Rizzo, Universita` di Pisa * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ /* * $Id$ * $FreeBSD$ * * A round-robin (RR) anticipatory scheduler, with per-client queues. * * The goal of this implementation is to improve throughput compared * to the pure elevator algorithm, and insure some fairness among * clients. * * Requests coming from the same client are put in the same queue. * We use anticipation to help reducing seeks, and each queue * is never served continuously for more than a given amount of * time or data. Queues are then served in a round-robin fashion. * * Each queue can be in any of the following states: * READY immediately serve the first pending request; * BUSY one request is under service, wait for completion; * IDLING do not serve incoming requests immediately, unless * they are "eligible" as defined later. * * Scheduling is made looking at the status of all queues, * and the first one in round-robin order is privileged. */ #include #include #include #include #include #include #include #include #include #include #include "gs_scheduler.h" /* possible states of the scheduler */ enum g_rr_state { G_QUEUE_READY = 0, /* Ready to dispatch. */ G_QUEUE_BUSY, /* Waiting for a completion. */ G_QUEUE_IDLING /* Waiting for a new request. */ }; /* possible queue flags */ enum g_rr_flags { G_FLAG_COMPLETED = 1, /* Completed a req. in the current budget. */ }; struct g_rr_softc; /* * Queue descriptor, containing reference count, scheduling * state, a queue of pending requests, configuration parameters. * Queues with pending request(s) and not under service are also * stored in a Round Robin (RR) list. */ struct g_rr_queue { struct g_rr_softc *q_sc; /* link to the parent */ enum g_rr_state q_status; unsigned int q_service; /* service received so far */ int q_slice_end; /* actual slice end in ticks */ enum g_rr_flags q_flags; /* queue flags */ struct bio_queue_head q_bioq; /* Scheduling parameters */ unsigned int q_budget; /* slice size in bytes */ unsigned int q_slice_duration; /* slice size in ticks */ unsigned int q_wait_ticks; /* wait time for anticipation */ /* Stats to drive the various heuristics. */ struct g_savg q_thinktime; /* Thinktime average. */ struct g_savg q_seekdist; /* Seek distance average. */ int q_bionum; /* Number of requests. */ off_t q_lastoff; /* Last submitted req. offset. */ int q_lastsub; /* Last submitted req. time. */ /* Expiration deadline for an empty queue. */ int q_expire; TAILQ_ENTRY(g_rr_queue) q_tailq; /* RR list link field */ }; /* List types. */ TAILQ_HEAD(g_rr_tailq, g_rr_queue); /* list of scheduler instances */ LIST_HEAD(g_scheds, g_rr_softc); /* Default quantum for RR between queues. */ #define G_RR_DEFAULT_BUDGET 0x00800000 /* * Per device descriptor, holding the Round Robin list of queues * accessing the disk, a reference to the geom, and the timer. */ struct g_rr_softc { struct g_geom *sc_geom; /* * sc_active is the queue we are anticipating for. * It is set only in gs_rr_next(), and possibly cleared * only in gs_rr_next() or on a timeout. * The active queue is never in the Round Robin list * even if it has requests queued. */ struct g_rr_queue *sc_active; struct callout sc_wait; /* timer for sc_active */ struct g_rr_tailq sc_rr_tailq; /* the round-robin list */ int sc_nqueues; /* number of queues */ /* Statistics */ int sc_in_flight; /* requests in the driver */ LIST_ENTRY(g_rr_softc) sc_next; }; /* Descriptor for bounded values, min and max are constant. */ struct x_bound { const int x_min; int x_cur; const int x_max; }; /* * parameters, config and stats */ struct g_rr_params { int queues; /* total number of queues */ int w_anticipate; /* anticipate writes */ int bypass; /* bypass scheduling writes */ int units; /* how many instances */ /* sc_head is used for debugging */ struct g_scheds sc_head; /* first scheduler instance */ struct x_bound queue_depth; /* max parallel requests */ struct x_bound wait_ms; /* wait time, milliseconds */ struct x_bound quantum_ms; /* quantum size, milliseconds */ struct x_bound quantum_kb; /* quantum size, Kb (1024 bytes) */ /* statistics */ int wait_hit; /* success in anticipation */ int wait_miss; /* failure in anticipation */ }; /* * Default parameters for the scheduler. The quantum sizes target * a 80MB/s disk; if the hw is faster or slower the minimum of the * two will have effect: the clients will still be isolated but * the fairness may be limited. A complete solution would involve * the on-line measurement of the actual disk throughput to derive * these parameters. Or we may just choose to ignore service domain * fairness and accept what can be achieved with time-only budgets. */ static struct g_rr_params me = { .sc_head = LIST_HEAD_INITIALIZER(&me.sc_head), .w_anticipate = 1, .queue_depth = { 1, 1, 50 }, .wait_ms = { 1, 10, 30 }, .quantum_ms = { 1, 100, 500 }, .quantum_kb = { 16, 8192, 65536 }, }; struct g_rr_params *gs_rr_me = &me; SYSCTL_DECL(_kern_geom_sched); SYSCTL_NODE(_kern_geom_sched, OID_AUTO, rr, CTLFLAG_RW, 0, "GEOM_SCHED ROUND ROBIN stuff"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, units, CTLFLAG_RD, &me.units, 0, "Scheduler instances"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, queues, CTLFLAG_RD, &me.queues, 0, "Total rr queues"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, wait_ms, CTLFLAG_RW, &me.wait_ms.x_cur, 0, "Wait time milliseconds"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, quantum_ms, CTLFLAG_RW, &me.quantum_ms.x_cur, 0, "Quantum size milliseconds"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, bypass, CTLFLAG_RW, &me.bypass, 0, "Bypass scheduler"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, w_anticipate, CTLFLAG_RW, &me.w_anticipate, 0, "Do anticipation on writes"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, quantum_kb, CTLFLAG_RW, &me.quantum_kb.x_cur, 0, "Quantum size Kbytes"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, queue_depth, CTLFLAG_RW, &me.queue_depth.x_cur, 0, "Maximum simultaneous requests"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, wait_hit, CTLFLAG_RW, &me.wait_hit, 0, "Hits in anticipation"); SYSCTL_UINT(_kern_geom_sched_rr, OID_AUTO, wait_miss, CTLFLAG_RW, &me.wait_miss, 0, "Misses in anticipation"); #ifdef DEBUG_QUEUES /* print the status of a queue */ static void gs_rr_dump_q(struct g_rr_queue *qp, int index) { int l = 0; struct bio *bp; TAILQ_FOREACH(bp, &(qp->q_bioq.queue), bio_queue) { l++; } printf("--- rr queue %d %p status %d len %d ---\n", index, qp, qp->q_status, l); } /* * Dump the scheduler status when writing to this sysctl variable. * XXX right now we only dump the status of the last instance created. * not a severe issue because this is only for debugging */ static int gs_rr_sysctl_status(SYSCTL_HANDLER_ARGS) { int error, val = 0; struct g_rr_softc *sc; error = sysctl_handle_int(oidp, &val, 0, req); if (error || !req->newptr ) return (error); printf("called %s\n", __FUNCTION__); LIST_FOREACH(sc, &me.sc_head, sc_next) { int i, tot = 0; printf("--- sc %p active %p nqueues %d " "callout %d in_flight %d ---\n", sc, sc->sc_active, sc->sc_nqueues, callout_active(&sc->sc_wait), sc->sc_in_flight); for (i = 0; i < G_RR_HASH_SIZE; i++) { struct g_rr_queue *qp; LIST_FOREACH(qp, &sc->sc_hash[i], q_hash) { gs_rr_dump_q(qp, tot); tot++; } } } return (0); } SYSCTL_PROC(_kern_geom_sched_rr, OID_AUTO, status, CTLTYPE_UINT | CTLFLAG_RW, 0, sizeof(int), gs_rr_sysctl_status, "I", "status"); #endif /* DEBUG_QUEUES */ /* * Get a bounded value, optionally convert to a min of t_min ticks. */ static int get_bounded(struct x_bound *v, int t_min) { int x; x = v->x_cur; if (x < v->x_min) x = v->x_min; else if (x > v->x_max) x = v->x_max; if (t_min) { x = x * hz / 1000; /* convert to ticks */ if (x < t_min) x = t_min; } return x; } /* * Get a reference to the queue for bp, using the generic * classification mechanism. */ static struct g_rr_queue * g_rr_queue_get(struct g_rr_softc *sc, struct bio *bp) { return (g_sched_get_class(sc->sc_geom, bp)); } static int g_rr_init_class(void *data, void *priv) { struct g_rr_softc *sc = data; struct g_rr_queue *qp = priv; gs_bioq_init(&qp->q_bioq); /* * Set the initial parameters for the client: * slice size in bytes and ticks, and wait ticks. * Right now these are constant, but we could have * autoconfiguration code to adjust the values based on * the actual workload. */ qp->q_budget = 1024 * get_bounded(&me.quantum_kb, 0); qp->q_slice_duration = get_bounded(&me.quantum_ms, 2); qp->q_wait_ticks = get_bounded(&me.wait_ms, 2); qp->q_sc = sc; /* link to the parent */ qp->q_sc->sc_nqueues++; me.queues++; return (0); } /* * Release a reference to the queue. */ static void g_rr_queue_put(struct g_rr_queue *qp) { g_sched_put_class(qp->q_sc->sc_geom, qp); } static void g_rr_fini_class(void *data, void *priv) { struct g_rr_queue *qp = priv; KASSERT(gs_bioq_first(&qp->q_bioq) == NULL, ("released nonempty queue")); qp->q_sc->sc_nqueues--; me.queues--; } static inline int g_rr_queue_expired(struct g_rr_queue *qp) { if (qp->q_service >= qp->q_budget) return (1); if ((qp->q_flags & G_FLAG_COMPLETED) && ticks - qp->q_slice_end >= 0) return (1); return (0); } static inline int g_rr_should_anticipate(struct g_rr_queue *qp, struct bio *bp) { int wait = get_bounded(&me.wait_ms, 2); if (!me.w_anticipate && (bp->bio_cmd & BIO_WRITE)) return (0); if (g_savg_valid(&qp->q_thinktime) && g_savg_read(&qp->q_thinktime) > wait) return (0); if (g_savg_valid(&qp->q_seekdist) && g_savg_read(&qp->q_seekdist) > 8192) return (0); return (1); } /* * Called on a request arrival, timeout or completion. * Try to serve a request among those queued. */ static struct bio * g_rr_next(void *data, int force) { struct g_rr_softc *sc = data; struct g_rr_queue *qp; struct bio *bp, *next; int expired; qp = sc->sc_active; if (me.bypass == 0 && !force) { if (sc->sc_in_flight >= get_bounded(&me.queue_depth, 0)) return (NULL); /* Try with the queue under service first. */ if (qp != NULL && qp->q_status != G_QUEUE_READY) { /* * Queue is anticipating, ignore request. * We should check that we are not past * the timeout, but in that case the timeout * will fire immediately afterwards so we * don't bother. */ return (NULL); } } else if (qp != NULL && qp->q_status != G_QUEUE_READY) { g_rr_queue_put(qp); sc->sc_active = qp = NULL; } /* * No queue under service, look for the first in RR order. * If we find it, select if as sc_active, clear service * and record the end time of the slice. */ if (qp == NULL) { qp = TAILQ_FIRST(&sc->sc_rr_tailq); if (qp == NULL) return (NULL); /* no queues at all, return */ /* otherwise select the new queue for service. */ TAILQ_REMOVE(&sc->sc_rr_tailq, qp, q_tailq); sc->sc_active = qp; qp->q_service = 0; qp->q_flags &= ~G_FLAG_COMPLETED; } bp = gs_bioq_takefirst(&qp->q_bioq); /* surely not NULL */ qp->q_service += bp->bio_length; /* charge the service */ /* * The request at the head of the active queue is always * dispatched, and gs_rr_next() will be called again * immediately. * We need to prepare for what to do next: * * 1. have we reached the end of the (time or service) slice ? * If so, clear sc_active and possibly requeue the previous * active queue if it has more requests pending; * 2. do we have more requests in sc_active ? * If yes, do not anticipate, as gs_rr_next() will run again; * if no, decide whether or not to anticipate depending * on read or writes (e.g., anticipate only on reads). */ expired = g_rr_queue_expired(qp); /* are we expired ? */ next = gs_bioq_first(&qp->q_bioq); /* do we have one more ? */ if (expired) { sc->sc_active = NULL; /* Either requeue or release reference. */ if (next != NULL) TAILQ_INSERT_TAIL(&sc->sc_rr_tailq, qp, q_tailq); else g_rr_queue_put(qp); } else if (next != NULL) { qp->q_status = G_QUEUE_READY; } else { if (!force && g_rr_should_anticipate(qp, bp)) { /* anticipate */ qp->q_status = G_QUEUE_BUSY; } else { /* do not anticipate, release reference */ g_rr_queue_put(qp); sc->sc_active = NULL; } } /* If sc_active != NULL, its q_status is always correct. */ sc->sc_in_flight++; return (bp); } static inline void g_rr_update_thinktime(struct g_rr_queue *qp) { int delta = ticks - qp->q_lastsub, wait = get_bounded(&me.wait_ms, 2); if (qp->q_sc->sc_active != qp) return; qp->q_lastsub = ticks; delta = (delta > 2 * wait) ? 2 * wait : delta; if (qp->q_bionum > 7) g_savg_add_sample(&qp->q_thinktime, delta); } static inline void g_rr_update_seekdist(struct g_rr_queue *qp, struct bio *bp) { off_t dist; if (qp->q_lastoff > bp->bio_offset) dist = qp->q_lastoff - bp->bio_offset; else dist = bp->bio_offset - qp->q_lastoff; if (dist > (8192 * 8)) dist = 8192 * 8; qp->q_lastoff = bp->bio_offset + bp->bio_length; if (qp->q_bionum > 7) g_savg_add_sample(&qp->q_seekdist, dist); } /* * Called when a real request for disk I/O arrives. * Locate the queue associated with the client. * If the queue is the one we are anticipating for, reset its timeout; * if the queue is not in the round robin list, insert it in the list. * On any error, do not queue the request and return -1, the caller * will take care of this request. */ static int g_rr_start(void *data, struct bio *bp) { struct g_rr_softc *sc = data; struct g_rr_queue *qp; if (me.bypass) return (-1); /* bypass the scheduler */ /* Get the queue for the request. */ qp = g_rr_queue_get(sc, bp); if (qp == NULL) return (-1); /* allocation failed, tell upstream */ if (gs_bioq_first(&qp->q_bioq) == NULL) { /* * We are inserting into an empty queue. * Reset its state if it is sc_active, * otherwise insert it in the RR list. */ if (qp == sc->sc_active) { qp->q_status = G_QUEUE_READY; callout_stop(&sc->sc_wait); } else { g_sched_priv_ref(qp); TAILQ_INSERT_TAIL(&sc->sc_rr_tailq, qp, q_tailq); } } qp->q_bionum = 1 + qp->q_bionum - (qp->q_bionum >> 3); g_rr_update_thinktime(qp); g_rr_update_seekdist(qp, bp); /* Inherit the reference returned by g_rr_queue_get(). */ bp->bio_caller1 = qp; gs_bioq_disksort(&qp->q_bioq, bp); return (0); } /* * Callout executed when a queue times out anticipating a new request. */ static void g_rr_wait_timeout(void *data) { struct g_rr_softc *sc = data; struct g_geom *geom = sc->sc_geom; g_sched_lock(geom); /* * We can race with other events, so check if * sc_active is still valid. */ if (sc->sc_active != NULL) { /* Release the reference to the queue. */ g_rr_queue_put(sc->sc_active); sc->sc_active = NULL; me.wait_hit--; me.wait_miss++; /* record the miss */ } g_sched_dispatch(geom); g_sched_unlock(geom); } /* * Module glue: allocate descriptor, initialize its fields. */ static void * g_rr_init(struct g_geom *geom) { struct g_rr_softc *sc; /* XXX check whether we can sleep */ sc = malloc(sizeof *sc, M_GEOM_SCHED, M_NOWAIT | M_ZERO); sc->sc_geom = geom; TAILQ_INIT(&sc->sc_rr_tailq); callout_init(&sc->sc_wait, CALLOUT_MPSAFE); LIST_INSERT_HEAD(&me.sc_head, sc, sc_next); me.units++; return (sc); } /* * Module glue -- drain the callout structure, destroy the * hash table and its element, and free the descriptor. */ static void g_rr_fini(void *data) { struct g_rr_softc *sc = data; callout_drain(&sc->sc_wait); KASSERT(sc->sc_active == NULL, ("still a queue under service")); KASSERT(TAILQ_EMPTY(&sc->sc_rr_tailq), ("still scheduled queues")); LIST_REMOVE(sc, sc_next); me.units--; free(sc, M_GEOM_SCHED); } /* * Called when the request under service terminates. * Start the anticipation timer if needed. */ static void g_rr_done(void *data, struct bio *bp) { struct g_rr_softc *sc = data; struct g_rr_queue *qp; sc->sc_in_flight--; qp = bp->bio_caller1; if (qp == sc->sc_active && qp->q_status == G_QUEUE_BUSY) { if (!(qp->q_flags & G_FLAG_COMPLETED)) { qp->q_flags |= G_FLAG_COMPLETED; /* in case we want to make the slice adaptive */ qp->q_slice_duration = get_bounded(&me.quantum_ms, 2); qp->q_slice_end = ticks + qp->q_slice_duration; } /* The queue is trying anticipation, start the timer. */ qp->q_status = G_QUEUE_IDLING; /* may make this adaptive */ qp->q_wait_ticks = get_bounded(&me.wait_ms, 2); me.wait_hit++; callout_reset(&sc->sc_wait, qp->q_wait_ticks, g_rr_wait_timeout, sc); } else g_sched_dispatch(sc->sc_geom); /* Release a reference to the queue. */ g_rr_queue_put(qp); } static void g_rr_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp, struct g_consumer *cp, struct g_provider *pp) { if (indent == NULL) { /* plaintext */ sbuf_printf(sb, " units %d queues %d", me.units, me.queues); } } static struct g_gsched g_rr = { .gs_name = "rr", .gs_priv_size = sizeof(struct g_rr_queue), .gs_init = g_rr_init, .gs_fini = g_rr_fini, .gs_start = g_rr_start, .gs_done = g_rr_done, .gs_next = g_rr_next, .gs_dumpconf = g_rr_dumpconf, .gs_init_class = g_rr_init_class, .gs_fini_class = g_rr_fini_class, }; DECLARE_GSCHED_MODULE(rr, &g_rr);