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/*-
* 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: release/9.1.0/sys/geom/sched/gs_rr.c 223921 2011-07-11 05:22:31Z ae $
*
* 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/bio.h>
#include <sys/callout.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#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 means that the field q_slice_end is valid. */
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 time, 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_INT(_kern_geom_sched_rr, OID_AUTO, units, CTLFLAG_RD,
&me.units, 0, "Scheduler instances");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, queues, CTLFLAG_RD,
&me.queues, 0, "Total rr queues");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, wait_ms, CTLFLAG_RW,
&me.wait_ms.x_cur, 0, "Wait time milliseconds");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, quantum_ms, CTLFLAG_RW,
&me.quantum_ms.x_cur, 0, "Quantum size milliseconds");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, bypass, CTLFLAG_RW,
&me.bypass, 0, "Bypass scheduler");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, w_anticipate, CTLFLAG_RW,
&me.w_anticipate, 0, "Do anticipation on writes");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, quantum_kb, CTLFLAG_RW,
&me.quantum_kb.x_cur, 0, "Quantum size Kbytes");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, queue_depth, CTLFLAG_RW,
&me.queue_depth.x_cur, 0, "Maximum simultaneous requests");
SYSCTL_INT(_kern_geom_sched_rr, OID_AUTO, wait_hit, CTLFLAG_RW,
&me.wait_hit, 0, "Hits in anticipation");
SYSCTL_INT(_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;
/*
* When the first request for this queue completes, update the
* duration and end of the slice. We do not do it when the
* slice starts to avoid charging to the queue the time for
* the first seek.
*/
if (!(qp->q_flags & G_FLAG_COMPLETED)) {
qp->q_flags |= G_FLAG_COMPLETED;
/*
* recompute the slice duration, in case we want
* to make it adaptive. This is not used right now.
* XXX should we do the same for q_quantum and q_wait_ticks ?
*/
qp->q_slice_duration = get_bounded(&me.quantum_ms, 2);
qp->q_slice_end = ticks + qp->q_slice_duration;
}
if (qp == sc->sc_active && qp->q_status == G_QUEUE_BUSY) {
/* 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);