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freebsd-dev/sys/cam/cam_iosched.c

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/*-
* CAM IO Scheduler Interface
*
* Copyright (c) 2015 Netflix, Inc.
* 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,
* without modification, immediately at the beginning of the file.
* 2. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* 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.
*
* $FreeBSD$
*/
#include "opt_cam.h"
#include "opt_ddb.h"
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/bio.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#include <cam/cam.h>
#include <cam/cam_ccb.h>
#include <cam/cam_periph.h>
#include <cam/cam_xpt_periph.h>
#include <cam/cam_xpt_internal.h>
#include <cam/cam_iosched.h>
#include <ddb/ddb.h>
static MALLOC_DEFINE(M_CAMSCHED, "CAM I/O Scheduler",
"CAM I/O Scheduler buffers");
/*
* Default I/O scheduler for FreeBSD. This implementation is just a thin-vineer
* over the bioq_* interface, with notions of separate calls for normal I/O and
* for trims.
*
* When CAM_IOSCHED_DYNAMIC is defined, the scheduler is enhanced to dynamically
* steer the rate of one type of traffic to help other types of traffic (eg
* limit writes when read latency deteriorates on SSDs).
*/
#ifdef CAM_IOSCHED_DYNAMIC
static int do_dynamic_iosched = 1;
TUNABLE_INT("kern.cam.do_dynamic_iosched", &do_dynamic_iosched);
SYSCTL_INT(_kern_cam, OID_AUTO, do_dynamic_iosched, CTLFLAG_RD,
&do_dynamic_iosched, 1,
"Enable Dynamic I/O scheduler optimizations.");
/*
* For an EMA, with an alpha of alpha, we know
* alpha = 2 / (N + 1)
* or
* N = 1 + (2 / alpha)
* where N is the number of samples that 86% of the current
* EMA is derived from.
*
* So we invent[*] alpha_bits:
* alpha_bits = -log_2(alpha)
* alpha = 2^-alpha_bits
* So
* N = 1 + 2^(alpha_bits + 1)
*
* The default 9 gives a 1025 lookback for 86% of the data.
* For a brief intro: https://en.wikipedia.org/wiki/Moving_average
*
* [*] Steal from the load average code and many other places.
*/
static int alpha_bits = 9;
TUNABLE_INT("kern.cam.iosched_alpha_bits", &alpha_bits);
SYSCTL_INT(_kern_cam, OID_AUTO, iosched_alpha_bits, CTLFLAG_RW,
&alpha_bits, 1,
"Bits in EMA's alpha.");
struct iop_stats;
struct cam_iosched_softc;
int iosched_debug = 0;
typedef enum {
none = 0, /* No limits */
queue_depth, /* Limit how many ops we queue to SIM */
iops, /* Limit # of IOPS to the drive */
bandwidth, /* Limit bandwidth to the drive */
limiter_max
} io_limiter;
static const char *cam_iosched_limiter_names[] =
{ "none", "queue_depth", "iops", "bandwidth" };
/*
* Called to initialize the bits of the iop_stats structure relevant to the
* limiter. Called just after the limiter is set.
*/
typedef int l_init_t(struct iop_stats *);
/*
* Called every tick.
*/
typedef int l_tick_t(struct iop_stats *);
/*
* Called to see if the limiter thinks this IOP can be allowed to
* proceed. If so, the limiter assumes that the while IOP proceeded
* and makes any accounting of it that's needed.
*/
typedef int l_iop_t(struct iop_stats *, struct bio *);
/*
* Called when an I/O completes so the limiter can updates its
* accounting. Pending I/Os may complete in any order (even when
* sent to the hardware at the same time), so the limiter may not
* make any assumptions other than this I/O has completed. If it
* returns 1, then xpt_schedule() needs to be called again.
*/
typedef int l_iodone_t(struct iop_stats *, struct bio *);
static l_iop_t cam_iosched_qd_iop;
static l_iop_t cam_iosched_qd_caniop;
static l_iodone_t cam_iosched_qd_iodone;
static l_init_t cam_iosched_iops_init;
static l_tick_t cam_iosched_iops_tick;
static l_iop_t cam_iosched_iops_caniop;
static l_iop_t cam_iosched_iops_iop;
static l_init_t cam_iosched_bw_init;
static l_tick_t cam_iosched_bw_tick;
static l_iop_t cam_iosched_bw_caniop;
static l_iop_t cam_iosched_bw_iop;
struct limswitch {
l_init_t *l_init;
l_tick_t *l_tick;
l_iop_t *l_iop;
l_iop_t *l_caniop;
l_iodone_t *l_iodone;
} limsw[] =
{
{ /* none */
.l_init = NULL,
.l_tick = NULL,
.l_iop = NULL,
.l_iodone= NULL,
},
{ /* queue_depth */
.l_init = NULL,
.l_tick = NULL,
.l_caniop = cam_iosched_qd_caniop,
.l_iop = cam_iosched_qd_iop,
.l_iodone= cam_iosched_qd_iodone,
},
{ /* iops */
.l_init = cam_iosched_iops_init,
.l_tick = cam_iosched_iops_tick,
.l_caniop = cam_iosched_iops_caniop,
.l_iop = cam_iosched_iops_iop,
.l_iodone= NULL,
},
{ /* bandwidth */
.l_init = cam_iosched_bw_init,
.l_tick = cam_iosched_bw_tick,
.l_caniop = cam_iosched_bw_caniop,
.l_iop = cam_iosched_bw_iop,
.l_iodone= NULL,
},
};
struct iop_stats {
/*
* sysctl state for this subnode.
*/
struct sysctl_ctx_list sysctl_ctx;
struct sysctl_oid *sysctl_tree;
/*
* Information about the current rate limiters, if any
*/
io_limiter limiter; /* How are I/Os being limited */
int min; /* Low range of limit */
int max; /* High range of limit */
int current; /* Current rate limiter */
int l_value1; /* per-limiter scratch value 1. */
int l_value2; /* per-limiter scratch value 2. */
/*
* Debug information about counts of I/Os that have gone through the
* scheduler.
*/
int pending; /* I/Os pending in the hardware */
int queued; /* number currently in the queue */
int total; /* Total for all time -- wraps */
int in; /* number queued all time -- wraps */
int out; /* number completed all time -- wraps */
/*
* Statistics on different bits of the process.
*/
/* Exp Moving Average, see alpha_bits for more details */
sbintime_t ema;
sbintime_t emss; /* Exp Moving sum of the squares */
sbintime_t sd; /* Last computed sd */
uint32_t state_flags;
#define IOP_RATE_LIMITED 1u
#define LAT_BUCKETS 12 /* < 1ms < 2ms ... 512ms < 1024ms > 1024ms */
uint64_t latencies[LAT_BUCKETS];
struct cam_iosched_softc *softc;
};
typedef enum {
set_max = 0, /* current = max */
read_latency, /* Steer read latency by throttling writes */
cl_max /* Keep last */
} control_type;
static const char *cam_iosched_control_type_names[] =
{ "set_max", "read_latency" };
struct control_loop {
/*
* sysctl state for this subnode.
*/
struct sysctl_ctx_list sysctl_ctx;
struct sysctl_oid *sysctl_tree;
sbintime_t next_steer; /* Time of next steer */
sbintime_t steer_interval; /* How often do we steer? */
sbintime_t lolat;
sbintime_t hilat;
int alpha;
control_type type; /* What type of control? */
int last_count; /* Last I/O count */
struct cam_iosched_softc *softc;
};
#endif
struct cam_iosched_softc {
struct bio_queue_head bio_queue;
struct bio_queue_head trim_queue;
/* scheduler flags < 16, user flags >= 16 */
uint32_t flags;
int sort_io_queue;
#ifdef CAM_IOSCHED_DYNAMIC
int read_bias; /* Read bias setting */
int current_read_bias; /* Current read bias state */
int total_ticks;
int load; /* EMA of 'load average' of disk / 2^16 */
struct bio_queue_head write_queue;
struct iop_stats read_stats, write_stats, trim_stats;
struct sysctl_ctx_list sysctl_ctx;
struct sysctl_oid *sysctl_tree;
int quanta; /* Number of quanta per second */
struct callout ticker; /* Callout for our quota system */
struct cam_periph *periph; /* cam periph associated with this device */
uint32_t this_frac; /* Fraction of a second (1024ths) for this tick */
sbintime_t last_time; /* Last time we ticked */
struct control_loop cl;
#endif
};
#ifdef CAM_IOSCHED_DYNAMIC
/*
* helper functions to call the limsw functions.
*/
static int
cam_iosched_limiter_init(struct iop_stats *ios)
{
int lim = ios->limiter;
/* maybe this should be a kassert */
if (lim < none || lim >= limiter_max)
return EINVAL;
if (limsw[lim].l_init)
return limsw[lim].l_init(ios);
return 0;
}
static int
cam_iosched_limiter_tick(struct iop_stats *ios)
{
int lim = ios->limiter;
/* maybe this should be a kassert */
if (lim < none || lim >= limiter_max)
return EINVAL;
if (limsw[lim].l_tick)
return limsw[lim].l_tick(ios);
return 0;
}
static int
cam_iosched_limiter_iop(struct iop_stats *ios, struct bio *bp)
{
int lim = ios->limiter;
/* maybe this should be a kassert */
if (lim < none || lim >= limiter_max)
return EINVAL;
if (limsw[lim].l_iop)
return limsw[lim].l_iop(ios, bp);
return 0;
}
static int
cam_iosched_limiter_caniop(struct iop_stats *ios, struct bio *bp)
{
int lim = ios->limiter;
/* maybe this should be a kassert */
if (lim < none || lim >= limiter_max)
return EINVAL;
if (limsw[lim].l_caniop)
return limsw[lim].l_caniop(ios, bp);
return 0;
}
static int
cam_iosched_limiter_iodone(struct iop_stats *ios, struct bio *bp)
{
int lim = ios->limiter;
/* maybe this should be a kassert */
if (lim < none || lim >= limiter_max)
return 0;
if (limsw[lim].l_iodone)
return limsw[lim].l_iodone(ios, bp);
return 0;
}
/*
* Functions to implement the different kinds of limiters
*/
static int
cam_iosched_qd_iop(struct iop_stats *ios, struct bio *bp)
{
if (ios->current <= 0 || ios->pending < ios->current)
return 0;
return EAGAIN;
}
static int
cam_iosched_qd_caniop(struct iop_stats *ios, struct bio *bp)
{
if (ios->current <= 0 || ios->pending < ios->current)
return 0;
return EAGAIN;
}
static int
cam_iosched_qd_iodone(struct iop_stats *ios, struct bio *bp)
{
if (ios->current <= 0 || ios->pending != ios->current)
return 0;
return 1;
}
static int
cam_iosched_iops_init(struct iop_stats *ios)
{
ios->l_value1 = ios->current / ios->softc->quanta;
if (ios->l_value1 <= 0)
ios->l_value1 = 1;
return 0;
}
static int
cam_iosched_iops_tick(struct iop_stats *ios)
{
ios->l_value1 = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
if (ios->l_value1 <= 0)
ios->l_value1 = 1;
return 0;
}
static int
cam_iosched_iops_caniop(struct iop_stats *ios, struct bio *bp)
{
/*
* So if we have any more IOPs left, allow it,
* otherwise wait.
*/
if (ios->l_value1 <= 0)
return EAGAIN;
return 0;
}
static int
cam_iosched_iops_iop(struct iop_stats *ios, struct bio *bp)
{
int rv;
rv = cam_iosched_limiter_caniop(ios, bp);
if (rv == 0)
ios->l_value1--;
return rv;
}
static int
cam_iosched_bw_init(struct iop_stats *ios)
{
/* ios->current is in kB/s, so scale to bytes */
ios->l_value1 = ios->current * 1000 / ios->softc->quanta;
return 0;
}
static int
cam_iosched_bw_tick(struct iop_stats *ios)
{
int bw;
/*
* If we're in the hole for available quota from
* the last time, then add the quantum for this.
* If we have any left over from last quantum,
* then too bad, that's lost. Also, ios->current
* is in kB/s, so scale.
*
* We also allow up to 4 quanta of credits to
* accumulate to deal with burstiness. 4 is extremely
* arbitrary.
*/
bw = (int)((ios->current * 1000ull * (uint64_t)ios->softc->this_frac) >> 16);
if (ios->l_value1 < bw * 4)
ios->l_value1 += bw;
return 0;
}
static int
cam_iosched_bw_caniop(struct iop_stats *ios, struct bio *bp)
{
/*
* So if we have any more bw quota left, allow it,
* otherwise wait. Not, we'll go negative and that's
* OK. We'll just get a lettle less next quota.
*
* Note on going negative: that allows us to process
* requests in order better, since we won't allow
* shorter reads to get around the long one that we
* don't have the quota to do just yet. It also prevents
* starvation by being a little more permissive about
* what we let through this quantum (to prevent the
* starvation), at the cost of getting a little less
* next quantum.
*/
if (ios->l_value1 <= 0)
return EAGAIN;
return 0;
}
static int
cam_iosched_bw_iop(struct iop_stats *ios, struct bio *bp)
{
int rv;
rv = cam_iosched_limiter_caniop(ios, bp);
if (rv == 0)
ios->l_value1 -= bp->bio_length;
return rv;
}
static void cam_iosched_cl_maybe_steer(struct control_loop *clp);
static void
cam_iosched_ticker(void *arg)
{
struct cam_iosched_softc *isc = arg;
sbintime_t now, delta;
int pending;
callout_reset(&isc->ticker, hz / isc->quanta - 1, cam_iosched_ticker, isc);
now = sbinuptime();
delta = now - isc->last_time;
isc->this_frac = (uint32_t)delta >> 16; /* Note: discards seconds -- should be 0 harmless if not */
isc->last_time = now;
cam_iosched_cl_maybe_steer(&isc->cl);
cam_iosched_limiter_tick(&isc->read_stats);
cam_iosched_limiter_tick(&isc->write_stats);
cam_iosched_limiter_tick(&isc->trim_stats);
cam_iosched_schedule(isc, isc->periph);
/*
* isc->load is an EMA of the pending I/Os at each tick. The number of
* pending I/Os is the sum of the I/Os queued to the hardware, and those
* in the software queue that could be queued to the hardware if there
* were slots.
*
* ios_stats.pending is a count of requests in the SIM right now for
* each of these types of I/O. So the total pending count is the sum of
* these I/Os and the sum of the queued I/Os still in the software queue
* for those operations that aren't being rate limited at the moment.
*
* The reason for the rate limiting bit is because those I/Os
* aren't part of the software queued load (since we could
* give them to hardware, but choose not to).
*
* Note: due to a bug in counting pending TRIM in the device, we
* don't include them in this count. We count each BIO_DELETE in
* the pending count, but the periph drivers collapse them down
* into one TRIM command. That one trim command gets the completion
* so the counts get off.
*/
pending = isc->read_stats.pending + isc->write_stats.pending /* + isc->trim_stats.pending */;
pending += !!(isc->read_stats.state_flags & IOP_RATE_LIMITED) * isc->read_stats.queued +
!!(isc->write_stats.state_flags & IOP_RATE_LIMITED) * isc->write_stats.queued /* +
!!(isc->trim_stats.state_flags & IOP_RATE_LIMITED) * isc->trim_stats.queued */ ;
pending <<= 16;
pending /= isc->periph->path->device->ccbq.total_openings;
isc->load = (pending + (isc->load << 13) - isc->load) >> 13; /* see above: 13 -> 16139 / 200/s = ~81s ~1 minute */
isc->total_ticks++;
}
static void
cam_iosched_cl_init(struct control_loop *clp, struct cam_iosched_softc *isc)
{
clp->next_steer = sbinuptime();
clp->softc = isc;
clp->steer_interval = SBT_1S * 5; /* Let's start out steering every 5s */
clp->lolat = 5 * SBT_1MS;
clp->hilat = 15 * SBT_1MS;
clp->alpha = 20; /* Alpha == gain. 20 = .2 */
clp->type = set_max;
}
static void
cam_iosched_cl_maybe_steer(struct control_loop *clp)
{
struct cam_iosched_softc *isc;
sbintime_t now, lat;
int old;
isc = clp->softc;
now = isc->last_time;
if (now < clp->next_steer)
return;
clp->next_steer = now + clp->steer_interval;
switch (clp->type) {
case set_max:
if (isc->write_stats.current != isc->write_stats.max)
printf("Steering write from %d kBps to %d kBps\n",
isc->write_stats.current, isc->write_stats.max);
isc->read_stats.current = isc->read_stats.max;
isc->write_stats.current = isc->write_stats.max;
isc->trim_stats.current = isc->trim_stats.max;
break;
case read_latency:
old = isc->write_stats.current;
lat = isc->read_stats.ema;
/*
* Simple PLL-like engine. Since we're steering to a range for
* the SP (set point) that makes things a little more
* complicated. In addition, we're not directly controlling our
* PV (process variable), the read latency, but instead are
* manipulating the write bandwidth limit for our MV
* (manipulation variable), analysis of this code gets a bit
* messy. Also, the MV is a very noisy control surface for read
* latency since it is affected by many hidden processes inside
* the device which change how responsive read latency will be
* in reaction to changes in write bandwidth. Unlike the classic
* boiler control PLL. this may result in over-steering while
* the SSD takes its time to react to the new, lower load. This
* is why we use a relatively low alpha of between .1 and .25 to
* compensate for this effect. At .1, it takes ~22 steering
* intervals to back off by a factor of 10. At .2 it only takes
* ~10. At .25 it only takes ~8. However some preliminary data
* from the SSD drives suggests a reasponse time in 10's of
* seconds before latency drops regardless of the new write
* rate. Careful observation will be reqiured to tune this
* effectively.
*
* Also, when there's no read traffic, we jack up the write
* limit too regardless of the last read latency. 10 is
* somewhat arbitrary.
*/
if (lat < clp->lolat || isc->read_stats.total - clp->last_count < 10)
isc->write_stats.current = isc->write_stats.current *
(100 + clp->alpha) / 100; /* Scale up */
else if (lat > clp->hilat)
isc->write_stats.current = isc->write_stats.current *
(100 - clp->alpha) / 100; /* Scale down */
clp->last_count = isc->read_stats.total;
/*
* Even if we don't steer, per se, enforce the min/max limits as
* those may have changed.
*/
if (isc->write_stats.current < isc->write_stats.min)
isc->write_stats.current = isc->write_stats.min;
if (isc->write_stats.current > isc->write_stats.max)
isc->write_stats.current = isc->write_stats.max;
if (old != isc->write_stats.current && iosched_debug)
printf("Steering write from %d kBps to %d kBps due to latency of %jdus\n",
old, isc->write_stats.current,
(uintmax_t)((uint64_t)1000000 * (uint32_t)lat) >> 32);
break;
case cl_max:
break;
}
}
#endif
/* Trim or similar currently pending completion */
#define CAM_IOSCHED_FLAG_TRIM_ACTIVE (1ul << 0)
/* Callout active, and needs to be torn down */
#define CAM_IOSCHED_FLAG_CALLOUT_ACTIVE (1ul << 1)
/* Periph drivers set these flags to indicate work */
#define CAM_IOSCHED_FLAG_WORK_FLAGS ((0xffffu) << 16)
#ifdef CAM_IOSCHED_DYNAMIC
static void
cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
sbintime_t sim_latency, int cmd, size_t size);
#endif
static inline int
cam_iosched_has_flagged_work(struct cam_iosched_softc *isc)
{
return !!(isc->flags & CAM_IOSCHED_FLAG_WORK_FLAGS);
}
static inline int
cam_iosched_has_io(struct cam_iosched_softc *isc)
{
#ifdef CAM_IOSCHED_DYNAMIC
if (do_dynamic_iosched) {
struct bio *rbp = bioq_first(&isc->bio_queue);
struct bio *wbp = bioq_first(&isc->write_queue);
int can_write = wbp != NULL &&
cam_iosched_limiter_caniop(&isc->write_stats, wbp) == 0;
int can_read = rbp != NULL &&
cam_iosched_limiter_caniop(&isc->read_stats, rbp) == 0;
if (iosched_debug > 2) {
printf("can write %d: pending_writes %d max_writes %d\n", can_write, isc->write_stats.pending, isc->write_stats.max);
printf("can read %d: read_stats.pending %d max_reads %d\n", can_read, isc->read_stats.pending, isc->read_stats.max);
printf("Queued reads %d writes %d\n", isc->read_stats.queued, isc->write_stats.queued);
}
return can_read || can_write;
}
#endif
return bioq_first(&isc->bio_queue) != NULL;
}
static inline int
cam_iosched_has_more_trim(struct cam_iosched_softc *isc)
{
return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) &&
bioq_first(&isc->trim_queue);
}
#define cam_iosched_sort_queue(isc) ((isc)->sort_io_queue >= 0 ? \
(isc)->sort_io_queue : cam_sort_io_queues)
static inline int
cam_iosched_has_work(struct cam_iosched_softc *isc)
{
#ifdef CAM_IOSCHED_DYNAMIC
if (iosched_debug > 2)
printf("has work: %d %d %d\n", cam_iosched_has_io(isc),
cam_iosched_has_more_trim(isc),
cam_iosched_has_flagged_work(isc));
#endif
return cam_iosched_has_io(isc) ||
cam_iosched_has_more_trim(isc) ||
cam_iosched_has_flagged_work(isc);
}
#ifdef CAM_IOSCHED_DYNAMIC
static void
cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios)
{
ios->limiter = none;
cam_iosched_limiter_init(ios);
ios->in = 0;
ios->max = 300000;
ios->min = 1;
ios->out = 0;
ios->pending = 0;
ios->queued = 0;
ios->total = 0;
ios->ema = 0;
ios->emss = 0;
ios->sd = 0;
ios->softc = isc;
}
static int
cam_iosched_limiter_sysctl(SYSCTL_HANDLER_ARGS)
{
char buf[16];
struct iop_stats *ios;
struct cam_iosched_softc *isc;
int value, i, error;
const char *p;
ios = arg1;
isc = ios->softc;
value = ios->limiter;
if (value < none || value >= limiter_max)
p = "UNKNOWN";
else
p = cam_iosched_limiter_names[value];
strlcpy(buf, p, sizeof(buf));
error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
if (error != 0 || req->newptr == NULL)
return error;
cam_periph_lock(isc->periph);
for (i = none; i < limiter_max; i++) {
if (strcmp(buf, cam_iosched_limiter_names[i]) != 0)
continue;
ios->limiter = i;
error = cam_iosched_limiter_init(ios);
if (error != 0) {
ios->limiter = value;
cam_periph_unlock(isc->periph);
return error;
}
/* Note: disk load averate requires ticker to be always running */
callout_reset(&isc->ticker, hz / isc->quanta - 1, cam_iosched_ticker, isc);
isc->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
cam_periph_unlock(isc->periph);
return 0;
}
cam_periph_unlock(isc->periph);
return EINVAL;
}
static int
cam_iosched_control_type_sysctl(SYSCTL_HANDLER_ARGS)
{
char buf[16];
struct control_loop *clp;
struct cam_iosched_softc *isc;
int value, i, error;
const char *p;
clp = arg1;
isc = clp->softc;
value = clp->type;
if (value < none || value >= cl_max)
p = "UNKNOWN";
else
p = cam_iosched_control_type_names[value];
strlcpy(buf, p, sizeof(buf));
error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
if (error != 0 || req->newptr == NULL)
return error;
for (i = set_max; i < cl_max; i++) {
if (strcmp(buf, cam_iosched_control_type_names[i]) != 0)
continue;
cam_periph_lock(isc->periph);
clp->type = i;
cam_periph_unlock(isc->periph);
return 0;
}
return EINVAL;
}
static int
cam_iosched_sbintime_sysctl(SYSCTL_HANDLER_ARGS)
{
char buf[16];
sbintime_t value;
int error;
uint64_t us;
value = *(sbintime_t *)arg1;
us = (uint64_t)value / SBT_1US;
snprintf(buf, sizeof(buf), "%ju", (intmax_t)us);
error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
if (error != 0 || req->newptr == NULL)
return error;
us = strtoul(buf, NULL, 10);
if (us == 0)
return EINVAL;
*(sbintime_t *)arg1 = us * SBT_1US;
return 0;
}
static int
cam_iosched_sysctl_latencies(SYSCTL_HANDLER_ARGS)
{
int i, error;
struct sbuf sb;
uint64_t *latencies;
latencies = arg1;
sbuf_new_for_sysctl(&sb, NULL, LAT_BUCKETS * 16, req);
for (i = 0; i < LAT_BUCKETS - 1; i++)
sbuf_printf(&sb, "%jd,", (intmax_t)latencies[i]);
sbuf_printf(&sb, "%jd", (intmax_t)latencies[LAT_BUCKETS - 1]);
error = sbuf_finish(&sb);
sbuf_delete(&sb);
return (error);
}
static void
cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stats *ios, char *name)
{
struct sysctl_oid_list *n;
struct sysctl_ctx_list *ctx;
ios->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, name,
CTLFLAG_RD, 0, name);
n = SYSCTL_CHILDREN(ios->sysctl_tree);
ctx = &ios->sysctl_ctx;
SYSCTL_ADD_UQUAD(ctx, n,
OID_AUTO, "ema", CTLFLAG_RD,
&ios->ema,
"Fast Exponentially Weighted Moving Average");
SYSCTL_ADD_UQUAD(ctx, n,
OID_AUTO, "emss", CTLFLAG_RD,
&ios->emss,
"Fast Exponentially Weighted Moving Sum of Squares (maybe wrong)");
SYSCTL_ADD_UQUAD(ctx, n,
OID_AUTO, "sd", CTLFLAG_RD,
&ios->sd,
"Estimated SD for fast ema (may be wrong)");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "pending", CTLFLAG_RD,
&ios->pending, 0,
"Instantaneous # of pending transactions");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "count", CTLFLAG_RD,
&ios->total, 0,
"# of transactions submitted to hardware");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "queued", CTLFLAG_RD,
&ios->queued, 0,
"# of transactions in the queue");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "in", CTLFLAG_RD,
&ios->in, 0,
"# of transactions queued to driver");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "out", CTLFLAG_RD,
&ios->out, 0,
"# of transactions completed");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "limiter", CTLTYPE_STRING | CTLFLAG_RW,
ios, 0, cam_iosched_limiter_sysctl, "A",
"Current limiting type.");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "min", CTLFLAG_RW,
&ios->min, 0,
"min resource");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "max", CTLFLAG_RW,
&ios->max, 0,
"max resource");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "current", CTLFLAG_RW,
&ios->current, 0,
"current resource");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "latencies", CTLTYPE_STRING | CTLFLAG_RD,
&ios->latencies, 0,
cam_iosched_sysctl_latencies, "A",
"Array of power of 2 latency from 1ms to 1.024s");
}
static void
cam_iosched_iop_stats_fini(struct iop_stats *ios)
{
if (ios->sysctl_tree)
if (sysctl_ctx_free(&ios->sysctl_ctx) != 0)
printf("can't remove iosched sysctl stats context\n");
}
static void
cam_iosched_cl_sysctl_init(struct cam_iosched_softc *isc)
{
struct sysctl_oid_list *n;
struct sysctl_ctx_list *ctx;
struct control_loop *clp;
clp = &isc->cl;
clp->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, "control",
CTLFLAG_RD, 0, "Control loop info");
n = SYSCTL_CHILDREN(clp->sysctl_tree);
ctx = &clp->sysctl_ctx;
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "type", CTLTYPE_STRING | CTLFLAG_RW,
clp, 0, cam_iosched_control_type_sysctl, "A",
"Control loop algorithm");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "steer_interval", CTLTYPE_STRING | CTLFLAG_RW,
&clp->steer_interval, 0, cam_iosched_sbintime_sysctl, "A",
"How often to steer (in us)");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "lolat", CTLTYPE_STRING | CTLFLAG_RW,
&clp->lolat, 0, cam_iosched_sbintime_sysctl, "A",
"Low water mark for Latency (in us)");
SYSCTL_ADD_PROC(ctx, n,
OID_AUTO, "hilat", CTLTYPE_STRING | CTLFLAG_RW,
&clp->hilat, 0, cam_iosched_sbintime_sysctl, "A",
"Hi water mark for Latency (in us)");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "alpha", CTLFLAG_RW,
&clp->alpha, 0,
"Alpha for PLL (x100) aka gain");
}
static void
cam_iosched_cl_sysctl_fini(struct control_loop *clp)
{
if (clp->sysctl_tree)
if (sysctl_ctx_free(&clp->sysctl_ctx) != 0)
printf("can't remove iosched sysctl control loop context\n");
}
#endif
/*
* Allocate the iosched structure. This also insulates callers from knowing
* sizeof struct cam_iosched_softc.
*/
int
cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph)
{
*iscp = malloc(sizeof(**iscp), M_CAMSCHED, M_NOWAIT | M_ZERO);
if (*iscp == NULL)
return ENOMEM;
#ifdef CAM_IOSCHED_DYNAMIC
if (iosched_debug)
printf("CAM IOSCHEDULER Allocating entry at %p\n", *iscp);
#endif
(*iscp)->sort_io_queue = -1;
bioq_init(&(*iscp)->bio_queue);
bioq_init(&(*iscp)->trim_queue);
#ifdef CAM_IOSCHED_DYNAMIC
if (do_dynamic_iosched) {
bioq_init(&(*iscp)->write_queue);
(*iscp)->read_bias = 100;
(*iscp)->current_read_bias = 100;
(*iscp)->quanta = 200;
cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats);
cam_iosched_iop_stats_init(*iscp, &(*iscp)->write_stats);
cam_iosched_iop_stats_init(*iscp, &(*iscp)->trim_stats);
(*iscp)->trim_stats.max = 1; /* Trims are special: one at a time for now */
(*iscp)->last_time = sbinuptime();
callout_init_mtx(&(*iscp)->ticker, cam_periph_mtx(periph), 0);
(*iscp)->periph = periph;
cam_iosched_cl_init(&(*iscp)->cl, *iscp);
callout_reset(&(*iscp)->ticker, hz / (*iscp)->quanta - 1, cam_iosched_ticker, *iscp);
(*iscp)->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
}
#endif
return 0;
}
/*
* Reclaim all used resources. This assumes that other folks have
* drained the requests in the hardware. Maybe an unwise assumption.
*/
void
cam_iosched_fini(struct cam_iosched_softc *isc)
{
if (isc) {
cam_iosched_flush(isc, NULL, ENXIO);
#ifdef CAM_IOSCHED_DYNAMIC
cam_iosched_iop_stats_fini(&isc->read_stats);
cam_iosched_iop_stats_fini(&isc->write_stats);
cam_iosched_iop_stats_fini(&isc->trim_stats);
cam_iosched_cl_sysctl_fini(&isc->cl);
if (isc->sysctl_tree)
if (sysctl_ctx_free(&isc->sysctl_ctx) != 0)
printf("can't remove iosched sysctl stats context\n");
if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) {
callout_drain(&isc->ticker);
isc->flags &= ~ CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
}
#endif
free(isc, M_CAMSCHED);
}
}
/*
* After we're sure we're attaching a device, go ahead and add
* hooks for any sysctl we may wish to honor.
*/
void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
struct sysctl_ctx_list *ctx, struct sysctl_oid *node)
{
#ifdef CAM_IOSCHED_DYNAMIC
struct sysctl_oid_list *n;
#endif
SYSCTL_ADD_INT(ctx, SYSCTL_CHILDREN(node),
OID_AUTO, "sort_io_queue", CTLFLAG_RW | CTLFLAG_MPSAFE,
&isc->sort_io_queue, 0,
"Sort IO queue to try and optimise disk access patterns");
#ifdef CAM_IOSCHED_DYNAMIC
if (!do_dynamic_iosched)
return;
isc->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
SYSCTL_CHILDREN(node), OID_AUTO, "iosched",
CTLFLAG_RD, 0, "I/O scheduler statistics");
n = SYSCTL_CHILDREN(isc->sysctl_tree);
ctx = &isc->sysctl_ctx;
cam_iosched_iop_stats_sysctl_init(isc, &isc->read_stats, "read");
cam_iosched_iop_stats_sysctl_init(isc, &isc->write_stats, "write");
cam_iosched_iop_stats_sysctl_init(isc, &isc->trim_stats, "trim");
cam_iosched_cl_sysctl_init(isc);
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "read_bias", CTLFLAG_RW,
&isc->read_bias, 100,
"How biased towards read should we be independent of limits");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "quanta", CTLFLAG_RW,
&isc->quanta, 200,
"How many quanta per second do we slice the I/O up into");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "total_ticks", CTLFLAG_RD,
&isc->total_ticks, 0,
"Total number of ticks we've done");
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "load", CTLFLAG_RD,
&isc->load, 0,
"scaled load average / 100");
#endif
}
/*
* Flush outstanding I/O. Consumers of this library don't know all the
* queues we may keep, so this allows all I/O to be flushed in one
* convenient call.
*/
void
cam_iosched_flush(struct cam_iosched_softc *isc, struct devstat *stp, int err)
{
bioq_flush(&isc->bio_queue, stp, err);
bioq_flush(&isc->trim_queue, stp, err);
#ifdef CAM_IOSCHED_DYNAMIC
if (do_dynamic_iosched)
bioq_flush(&isc->write_queue, stp, err);
#endif
}
#ifdef CAM_IOSCHED_DYNAMIC
static struct bio *
cam_iosched_get_write(struct cam_iosched_softc *isc)
{
struct bio *bp;
/*
* We control the write rate by controlling how many requests we send
* down to the drive at any one time. Fewer requests limits the
* effects of both starvation when the requests take a while and write
* amplification when each request is causing more than one write to
* the NAND media. Limiting the queue depth like this will also limit
* the write throughput and give and reads that want to compete to
* compete unfairly.
*/
bp = bioq_first(&isc->write_queue);
if (bp == NULL) {
if (iosched_debug > 3)
printf("No writes present in write_queue\n");
return NULL;
}
/*
* If pending read, prefer that based on current read bias
* setting.
*/
if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
if (iosched_debug)
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);
isc->current_read_bias--;
/* We're not limiting writes, per se, just doing reads first */
return NULL;
}
/*
* See if our current limiter allows this I/O.
*/
if (cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) {
if (iosched_debug)
printf("Can't write because limiter says no.\n");
isc->write_stats.state_flags |= IOP_RATE_LIMITED;
return NULL;
}
/*
* Let's do this: We've passed all the gates and we're a go
* to schedule the I/O in the SIM.
*/
isc->current_read_bias = isc->read_bias;
bioq_remove(&isc->write_queue, bp);
if (bp->bio_cmd == BIO_WRITE) {
isc->write_stats.queued--;
isc->write_stats.total++;
isc->write_stats.pending++;
}
if (iosched_debug > 9)
printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
isc->write_stats.state_flags &= ~IOP_RATE_LIMITED;
return bp;
}
#endif
/*
* Put back a trim that you weren't able to actually schedule this time.
*/
void
cam_iosched_put_back_trim(struct cam_iosched_softc *isc, struct bio *bp)
{
bioq_insert_head(&isc->trim_queue, bp);
#ifdef CAM_IOSCHED_DYNAMIC
isc->trim_stats.queued++;
isc->trim_stats.total--; /* since we put it back, don't double count */
isc->trim_stats.pending--;
#endif
}
/*
* gets the next trim from the trim queue.
*
* Assumes we're called with the periph lock held. It removes this
* trim from the queue and the device must explicitly reinstert it
* should the need arise.
*/
struct bio *
cam_iosched_next_trim(struct cam_iosched_softc *isc)
{
struct bio *bp;
bp = bioq_first(&isc->trim_queue);
if (bp == NULL)
return NULL;
bioq_remove(&isc->trim_queue, bp);
#ifdef CAM_IOSCHED_DYNAMIC
isc->trim_stats.queued--;
isc->trim_stats.total++;
isc->trim_stats.pending++;
#endif
return bp;
}
/*
* gets the an available trim from the trim queue, if there's no trim
* already pending. It removes this trim from the queue and the device
* must explicitly reinstert it should the need arise.
*
* Assumes we're called with the periph lock held.
*/
struct bio *
cam_iosched_get_trim(struct cam_iosched_softc *isc)
{
if (!cam_iosched_has_more_trim(isc))
return NULL;
return cam_iosched_next_trim(isc);
}
/*
* Determine what the next bit of work to do is for the periph. The
* default implementation looks to see if we have trims to do, but no
* trims outstanding. If so, we do that. Otherwise we see if we have
* other work. If we do, then we do that. Otherwise why were we called?
*/
struct bio *
cam_iosched_next_bio(struct cam_iosched_softc *isc)
{
struct bio *bp;
/*
* See if we have a trim that can be scheduled. We can only send one
* at a time down, so this takes that into account.
*
* XXX newer TRIM commands are queueable. Revisit this when we
* implement them.
*/
if ((bp = cam_iosched_get_trim(isc)) != NULL)
return bp;
#ifdef CAM_IOSCHED_DYNAMIC
/*
* See if we have any pending writes, and room in the queue for them,
* and if so, those are next.
*/
if (do_dynamic_iosched) {
if ((bp = cam_iosched_get_write(isc)) != NULL)
return bp;
}
#endif
/*
* next, see if there's other, normal I/O waiting. If so return that.
*/
if ((bp = bioq_first(&isc->bio_queue)) == NULL)
return NULL;
#ifdef CAM_IOSCHED_DYNAMIC
/*
* For the dynamic scheduler, bio_queue is only for reads, so enforce
* the limits here. Enforce only for reads.
*/
if (do_dynamic_iosched) {
if (bp->bio_cmd == BIO_READ &&
cam_iosched_limiter_iop(&isc->read_stats, bp) != 0) {
isc->read_stats.state_flags |= IOP_RATE_LIMITED;
return NULL;
}
}
isc->read_stats.state_flags &= ~IOP_RATE_LIMITED;
#endif
bioq_remove(&isc->bio_queue, bp);
#ifdef CAM_IOSCHED_DYNAMIC
if (do_dynamic_iosched) {
if (bp->bio_cmd == BIO_READ) {
isc->read_stats.queued--;
isc->read_stats.total++;
isc->read_stats.pending++;
} else
printf("Found bio_cmd = %#x\n", bp->bio_cmd);
}
if (iosched_debug > 9)
printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
#endif
return bp;
}
/*
* Driver has been given some work to do by the block layer. Tell the
* scheduler about it and have it queue the work up. The scheduler module
* will then return the currently most useful bit of work later, possibly
* deferring work for various reasons.
*/
void
cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp)
{
/*
* Put all trims on the trim queue sorted, since we know
* that the collapsing code requires this. Otherwise put
* the work on the bio queue.
*/
if (bp->bio_cmd == BIO_DELETE) {
bioq_disksort(&isc->trim_queue, bp);
#ifdef CAM_IOSCHED_DYNAMIC
isc->trim_stats.in++;
isc->trim_stats.queued++;
#endif
}
#ifdef CAM_IOSCHED_DYNAMIC
else if (do_dynamic_iosched &&
(bp->bio_cmd == BIO_WRITE || bp->bio_cmd == BIO_FLUSH)) {
if (cam_iosched_sort_queue(isc))
bioq_disksort(&isc->write_queue, bp);
else
bioq_insert_tail(&isc->write_queue, bp);
if (iosched_debug > 9)
printf("Qw : %p %#x\n", bp, bp->bio_cmd);
if (bp->bio_cmd == BIO_WRITE) {
isc->write_stats.in++;
isc->write_stats.queued++;
}
}
#endif
else {
if (cam_iosched_sort_queue(isc))
bioq_disksort(&isc->bio_queue, bp);
else
bioq_insert_tail(&isc->bio_queue, bp);
#ifdef CAM_IOSCHED_DYNAMIC
if (iosched_debug > 9)
printf("Qr : %p %#x\n", bp, bp->bio_cmd);
if (bp->bio_cmd == BIO_READ) {
isc->read_stats.in++;
isc->read_stats.queued++;
} else if (bp->bio_cmd == BIO_WRITE) {
isc->write_stats.in++;
isc->write_stats.queued++;
}
#endif
}
}
/*
* If we have work, get it scheduled. Called with the periph lock held.
*/
void
cam_iosched_schedule(struct cam_iosched_softc *isc, struct cam_periph *periph)
{
if (cam_iosched_has_work(isc))
xpt_schedule(periph, CAM_PRIORITY_NORMAL);
}
/*
* Complete a trim request
*/
void
cam_iosched_trim_done(struct cam_iosched_softc *isc)
{
isc->flags &= ~CAM_IOSCHED_FLAG_TRIM_ACTIVE;
}
/*
* Complete a bio. Called before we release the ccb with xpt_release_ccb so we
* might use notes in the ccb for statistics.
*/
int
cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp,
union ccb *done_ccb)
{
int retval = 0;
#ifdef CAM_IOSCHED_DYNAMIC
if (!do_dynamic_iosched)
return retval;
if (iosched_debug > 10)
printf("done: %p %#x\n", bp, bp->bio_cmd);
if (bp->bio_cmd == BIO_WRITE) {
retval = cam_iosched_limiter_iodone(&isc->write_stats, bp);
isc->write_stats.out++;
isc->write_stats.pending--;
} else if (bp->bio_cmd == BIO_READ) {
retval = cam_iosched_limiter_iodone(&isc->read_stats, bp);
isc->read_stats.out++;
isc->read_stats.pending--;
} else if (bp->bio_cmd == BIO_DELETE) {
isc->trim_stats.out++;
isc->trim_stats.pending--;
} else if (bp->bio_cmd != BIO_FLUSH) {
if (iosched_debug)
printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd);
}
if (!(bp->bio_flags & BIO_ERROR))
cam_iosched_io_metric_update(isc, done_ccb->ccb_h.qos.sim_data,
bp->bio_cmd, bp->bio_bcount);
#endif
return retval;
}
/*
* Tell the io scheduler that you've pushed a trim down into the sim.
* xxx better place for this?
*/
void
cam_iosched_submit_trim(struct cam_iosched_softc *isc)
{
isc->flags |= CAM_IOSCHED_FLAG_TRIM_ACTIVE;
}
/*
* Change the sorting policy hint for I/O transactions for this device.
*/
void
cam_iosched_set_sort_queue(struct cam_iosched_softc *isc, int val)
{
isc->sort_io_queue = val;
}
int
cam_iosched_has_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
{
return isc->flags & flags;
}
void
cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
{
isc->flags |= flags;
}
void
cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
{
isc->flags &= ~flags;
}
#ifdef CAM_IOSCHED_DYNAMIC
/*
* After the method presented in Jack Crenshaw's 1998 article "Integer
* Suqare Roots," reprinted at
* http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4219659/Integer-Square-Roots
* and well worth the read. Briefly, we find the power of 4 that's the
* largest smaller than val. We then check each smaller power of 4 to
* see if val is still bigger. The right shifts at each step divide
* the result by 2 which after successive application winds up
* accumulating the right answer. It could also have been accumulated
* using a separate root counter, but this code is smaller and faster
* than that method. This method is also integer size invariant.
* It returns floor(sqrt((float)val)), or the larget integer less than
* or equal to the square root.
*/
static uint64_t
isqrt64(uint64_t val)
{
uint64_t res = 0;
uint64_t bit = 1ULL << (sizeof(uint64_t) * NBBY - 2);
/*
* Find the largest power of 4 smaller than val.
*/
while (bit > val)
bit >>= 2;
/*
* Accumulate the answer, one bit at a time (we keep moving
* them over since 2 is the square root of 4 and we test
* powers of 4). We accumulate where we find the bit, but
* the successive shifts land the bit in the right place
* by the end.
*/
while (bit != 0) {
if (val >= res + bit) {
val -= res + bit;
res = (res >> 1) + bit;
} else
res >>= 1;
bit >>= 2;
}
return res;
}
/*
* a and b are 32.32 fixed point stored in a 64-bit word.
* Let al and bl be the .32 part of a and b.
* Let ah and bh be the 32 part of a and b.
* R is the radix and is 1 << 32
*
* a * b
* (ah + al / R) * (bh + bl / R)
* ah * bh + (al * bh + ah * bl) / R + al * bl / R^2
*
* After multiplicaiton, we have to renormalize by multiply by
* R, so we wind up with
* ah * bh * R + al * bh + ah * bl + al * bl / R
* which turns out to be a very nice way to compute this value
* so long as ah and bh are < 65536 there's no loss of high bits
* and the low order bits are below the threshold of caring for
* this application.
*/
static uint64_t
mul(uint64_t a, uint64_t b)
{
uint64_t al, ah, bl, bh;
al = a & 0xffffffff;
ah = a >> 32;
bl = b & 0xffffffff;
bh = b >> 32;
return ((ah * bh) << 32) + al * bh + ah * bl + ((al * bl) >> 32);
}
static sbintime_t latencies[] = {
SBT_1MS << 0,
SBT_1MS << 1,
SBT_1MS << 2,
SBT_1MS << 3,
SBT_1MS << 4,
SBT_1MS << 5,
SBT_1MS << 6,
SBT_1MS << 7,
SBT_1MS << 8,
SBT_1MS << 9,
SBT_1MS << 10
};
static void
cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency)
{
sbintime_t y, yy;
uint64_t var;
int i;
/*
* Keep counts for latency. We do it by power of two buckets.
* This helps us spot outlier behavior obscured by averages.
*/
for (i = 0; i < LAT_BUCKETS - 1; i++) {
if (sim_latency < latencies[i]) {
iop->latencies[i]++;
break;
}
}
if (i == LAT_BUCKETS - 1)
iop->latencies[i]++; /* Put all > 1024ms values into the last bucket. */
/*
* Classic expoentially decaying average with a tiny alpha
* (2 ^ -alpha_bits). For more info see the NIST statistical
* handbook.
*
* ema_t = y_t * alpha + ema_t-1 * (1 - alpha)
* alpha = 1 / (1 << alpha_bits)
*
* Since alpha is a power of two, we can compute this w/o any mult or
* division.
*/
y = sim_latency;
iop->ema = (y + (iop->ema << alpha_bits) - iop->ema) >> alpha_bits;
yy = mul(y, y);
iop->emss = (yy + (iop->emss << alpha_bits) - iop->emss) >> alpha_bits;
/*
* s_1 = sum of data
* s_2 = sum of data * data
* ema ~ mean (or s_1 / N)
* emss ~ s_2 / N
*
* sd = sqrt((N * s_2 - s_1 ^ 2) / (N * (N - 1)))
* sd = sqrt((N * s_2 / N * (N - 1)) - (s_1 ^ 2 / (N * (N - 1))))
*
* N ~ 2 / alpha - 1
* alpha < 1 / 16 (typically much less)
* N > 31 --> N large so N * (N - 1) is approx N * N
*
* substituting and rearranging:
* sd ~ sqrt(s_2 / N - (s_1 / N) ^ 2)
* ~ sqrt(emss - ema ^ 2);
* which is the formula used here to get a decent estimate of sd which
* we use to detect outliers. Note that when first starting up, it
* takes a while for emss sum of squares estimator to converge on a
* good value. during this time, it can be less than ema^2. We
* compute a sd of 0 in that case, and ignore outliers.
*/
var = iop->emss - mul(iop->ema, iop->ema);
iop->sd = (int64_t)var < 0 ? 0 : isqrt64(var);
}
static void
cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
sbintime_t sim_latency, int cmd, size_t size)
{
/* xxx Do we need to scale based on the size of the I/O ? */
switch (cmd) {
case BIO_READ:
cam_iosched_update(&isc->read_stats, sim_latency);
break;
case BIO_WRITE:
cam_iosched_update(&isc->write_stats, sim_latency);
break;
case BIO_DELETE:
cam_iosched_update(&isc->trim_stats, sim_latency);
break;
default:
break;
}
}
#ifdef DDB
static int biolen(struct bio_queue_head *bq)
{
int i = 0;
struct bio *bp;
TAILQ_FOREACH(bp, &bq->queue, bio_queue) {
i++;
}
return i;
}
/*
* Show the internal state of the I/O scheduler.
*/
DB_SHOW_COMMAND(iosched, cam_iosched_db_show)
{
struct cam_iosched_softc *isc;
if (!have_addr) {
db_printf("Need addr\n");
return;
}
isc = (struct cam_iosched_softc *)addr;
db_printf("pending_reads: %d\n", isc->read_stats.pending);
db_printf("min_reads: %d\n", isc->read_stats.min);
db_printf("max_reads: %d\n", isc->read_stats.max);
db_printf("reads: %d\n", isc->read_stats.total);
db_printf("in_reads: %d\n", isc->read_stats.in);
db_printf("out_reads: %d\n", isc->read_stats.out);
db_printf("queued_reads: %d\n", isc->read_stats.queued);
db_printf("Current Q len %d\n", biolen(&isc->bio_queue));
db_printf("pending_writes: %d\n", isc->write_stats.pending);
db_printf("min_writes: %d\n", isc->write_stats.min);
db_printf("max_writes: %d\n", isc->write_stats.max);
db_printf("writes: %d\n", isc->write_stats.total);
db_printf("in_writes: %d\n", isc->write_stats.in);
db_printf("out_writes: %d\n", isc->write_stats.out);
db_printf("queued_writes: %d\n", isc->write_stats.queued);
db_printf("Current Q len %d\n", biolen(&isc->write_queue));
db_printf("pending_trims: %d\n", isc->trim_stats.pending);
db_printf("min_trims: %d\n", isc->trim_stats.min);
db_printf("max_trims: %d\n", isc->trim_stats.max);
db_printf("trims: %d\n", isc->trim_stats.total);
db_printf("in_trims: %d\n", isc->trim_stats.in);
db_printf("out_trims: %d\n", isc->trim_stats.out);
db_printf("queued_trims: %d\n", isc->trim_stats.queued);
db_printf("Current Q len %d\n", biolen(&isc->trim_queue));
db_printf("read_bias: %d\n", isc->read_bias);
db_printf("current_read_bias: %d\n", isc->current_read_bias);
db_printf("Trim active? %s\n",
(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) ? "yes" : "no");
}
#endif
#endif
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