Re: [Qemu-devel] [PATCH V5 1/5] throttle: Add a new throttling API implementing continuous leaky bucket.

[Fam Zheng]

On Mon, 08/12 18:53, Benoît Canet wrote:
> Implement the continuous leaky bucket algorithm devised on IRC as a separate
> module.
> 
> Signed-off-by: Benoit Canet <address@hidden>
> ---
>  include/qemu/throttle.h |  105 +++++++++++++
>  util/Makefile.objs      |    1 +
>  util/throttle.c         |  391 
> +++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 497 insertions(+)
>  create mode 100644 include/qemu/throttle.h
>  create mode 100644 util/throttle.c
> 
> diff --git a/include/qemu/throttle.h b/include/qemu/throttle.h
> new file mode 100644
> index 0000000..e03bc3e
> --- /dev/null
> +++ b/include/qemu/throttle.h
> @@ -0,0 +1,105 @@
> +/*
> + * QEMU throttling infrastructure
> + *
> + * Copyright (C) Nodalink, SARL. 2013
> + *
> + * Author:
> + *   Benoît Canet <address@hidden>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 or
> + * (at your option) version 3 of the License.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef THROTTLING_H
> +#define THROTTLING_H
> +
> +#include <stdint.h>
> +#include "qemu-common.h"
> +#include "qemu/timer.h"
> +
> +#define NANOSECONDS_PER_SECOND  1000000000.0
> +
> +#define BUCKETS_COUNT 6
> +
> +typedef enum {
> +    THROTTLE_BPS_TOTAL = 0,
> +    THROTTLE_BPS_READ  = 1,
> +    THROTTLE_BPS_WRITE = 2,
> +    THROTTLE_OPS_TOTAL = 3,
> +    THROTTLE_OPS_READ  = 4,
> +    THROTTLE_OPS_WRITE = 5,
> +} BucketType;
> +
> +typedef struct LeakyBucket {
> +    double  ups;            /* units per second */
> +    double  max;            /* leaky bucket max in units */
> +    double  bucket;         /* bucket in units */
> +} LeakyBucket;
> +
> +/* The following structure is used to configure a ThrottleState
> + * It contains a bit of state: the bucket field of the LeakyBucket structure.
> + * However it allows to keep the code clean and the bucket field is reset to
> + * zero at the right time.
> + */
> +typedef struct ThrottleConfig {
> +    LeakyBucket buckets[6]; /* leaky buckets */
> +    uint64_t unit_size;     /* size of an unit in bytes */
> +    uint64_t op_size;       /* size of an operation in units */
> +} ThrottleConfig;
> +
> +typedef struct ThrottleState {
> +    ThrottleConfig cfg;     /* configuration */
> +    int64_t previous_leak;  /* timestamp of the last leak done */
> +    QEMUTimer * timers[2];  /* timers used to do the throttling */
> +    QEMUClock *clock;       /* the clock used */
> +} ThrottleState;
> +
> +/* operations on single leaky buckets */
> +void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta);
> +
> +int64_t throttle_compute_wait(LeakyBucket *bkt);
> +
> +/* expose timer computation function for unit tests */
> +bool throttle_compute_timer(ThrottleState *ts,
> +                            bool is_write,
> +                            int64_t now,
> +                            int64_t *next_timer);
> +
> +/* init/destroy cycle */
> +void throttle_init(ThrottleState *ts,
> +                   QEMUClock *clock,
> +                   void (read_timer)(void *),
> +                   void (write_timer)(void *),
> +                   void *timer_opaque);
> +
> +void throttle_destroy(ThrottleState *ts);
> +
> +bool throttle_have_timer(ThrottleState *ts);
> +
> +/* configuration */
> +bool throttle_enabled(ThrottleConfig *cfg);
> +
> +bool throttle_conflicting(ThrottleConfig *cfg);
> +
> +bool throttle_is_valid(ThrottleConfig *cfg);
> +
> +void throttle_config(ThrottleState *ts, ThrottleConfig *cfg);
> +
> +void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg);
> +
> +/* usage */
> +bool throttle_allowed(ThrottleState *ts, bool is_write);
> +
> +void throttle_account(ThrottleState *ts, bool is_write, uint64_t size);
> +
> +#endif
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index dc72ab0..2bb13a2 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -11,3 +11,4 @@ util-obj-y += iov.o aes.o qemu-config.o qemu-sockets.o 
> uri.o notify.o
>  util-obj-y += qemu-option.o qemu-progress.o
>  util-obj-y += hexdump.o
>  util-obj-y += crc32c.o
> +util-obj-y += throttle.o
> diff --git a/util/throttle.c b/util/throttle.c
> new file mode 100644
> index 0000000..2f25d44
> --- /dev/null
> +++ b/util/throttle.c
> @@ -0,0 +1,391 @@
> +/*
> + * QEMU throttling infrastructure
> + *
> + * Copyright (C) Nodalink, SARL. 2013
> + *
> + * Author:
> + *   Benoît Canet <address@hidden>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 or
> + * (at your option) version 3 of the License.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include "qemu/throttle.h"
> +#include "qemu/timer.h"
> +
> +/* This function make a bucket leak
> + *
> + * @bkt:   the bucket to make leak
> + * @delta: the time delta
> + */
> +void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta)
> +{
> +    double leak;
> +
> +    /* compute how much to leak */
> +    leak = (bkt->ups * (double) delta) / NANOSECONDS_PER_SECOND;
> +
> +    /* make the bucket leak */
> +    bkt->bucket = MAX(bkt->bucket - leak, 0);
> +}
> +
> +/* Calculate the time delta since last leak and make proportionals leaks
> + *
> + * @now:      the current timestamp in ns
> + */
> +static void throttle_do_leak(ThrottleState *ts, int64_t now)
> +{
> +    /* compute the time elapsed since the last leak */
> +    int64_t delta = now - ts->previous_leak;
> +    int i;
> +
> +    ts->previous_leak = now;
> +
> +    if (delta <= 0) {
> +        return;
> +    }
> +
> +    /* make each bucket leak */
> +    for (i = 0; i < BUCKETS_COUNT; i++) {
> +        throttle_leak_bucket(&ts->cfg.buckets[i], delta);
> +    }
> +}
> +
> +/* do the real job of computing the time to wait
> + *
> + * @limit: the throttling limit
> + * @extra: the number of operation to delay
> + * @ret:   the time to wait in ns
> + */
> +static int64_t throttle_do_compute_wait(double limit, double extra)
> +{
> +    double wait = extra * NANOSECONDS_PER_SECOND;
> +    wait /= limit;
> +    return wait;
> +}
> +
> +/* This function compute the wait time in ns that a leaky bucket should 
> trigger
> + *
> + * @bkt: the leaky bucket we operate on
> + * @ret: the resulting wait time in ns or 0 if the operation can go through
> + */
> +int64_t throttle_compute_wait(LeakyBucket *bkt)
> +{
> +    double extra; /* the number of extra units blocking the io */
> +
> +    if (!bkt->ups) {
> +        return 0;
> +    }
> +
> +    extra = bkt->bucket - bkt->max;
> +
> +    if (extra <= 0) {
> +        return 0;
> +    }
> +
> +    return throttle_do_compute_wait(bkt->ups, extra);
> +}
> +
> +/* This function compute the time that must be waited while this IO
> + *
> + * @is_write:   true if the current IO is a write, false if it's a read
> + * @ret:        time to wait
> + */
> +static int64_t throttle_compute_wait_for(ThrottleState *ts,
> +                                         bool is_write,
> +                                         int64_t now)

Parameter "now" not used.

> +{
> +    BucketType to_check[2][4] = { {THROTTLE_BPS_TOTAL,
> +                                   THROTTLE_OPS_TOTAL,
> +                                   THROTTLE_BPS_READ,
> +                                   THROTTLE_OPS_READ},
> +                                  {THROTTLE_BPS_TOTAL,
> +                                   THROTTLE_OPS_TOTAL,
> +                                   THROTTLE_BPS_WRITE,
> +                                   THROTTLE_OPS_WRITE}, };
> +    int64_t wait, max_wait = 0;
> +    int i;
> +
> +    for (i = 0; i < 4; i++) {
> +        BucketType index = to_check[is_write][i];
> +        wait = throttle_compute_wait(&ts->cfg.buckets[index]);
> +        if (wait > max_wait) {
> +            max_wait = wait;
> +        }
> +    }
> +
> +    return max_wait;
> +}
> +
> +/* compute the timer for this type of operation
> + *
> + * @is_write:   the type of operation
> + * @now:        the current clock timerstamp

s/timerstamp/timestamp/

> + * @next_timer: the resulting timer

A bit confusing with the name and description. This is actually a computed
timestamp for next triggering of the timer, right?

> + * @ret:        true if a timer must be set
> + */
> +bool throttle_compute_timer(ThrottleState *ts,
> +                            bool is_write,
> +                            int64_t now,
> +                            int64_t *next_timer)
> +{
> +    int64_t wait;
> +
> +    /* leak proportionally to the time elapsed */
> +    throttle_do_leak(ts, now);
> +
> +    /* compute the wait time if any */
> +    wait = throttle_compute_wait_for(ts, is_write, now);
> +
> +    /* if the code must wait compute when the next timer should fire */
> +    if (wait) {
> +        *next_timer = now + wait;
> +        return true;
> +    }
> +
> +    /* else no need to wait at all */
> +    *next_timer = now;
> +    return false;
> +}
> +
> +/* To be called first on the ThrottleState */
> +void throttle_init(ThrottleState *ts,
> +                   QEMUClock *clock,
> +                   void (read_timer)(void *),

There's a type name for this:

                      QEMUTimerCB * read_timer_cb,

> +                   void (write_timer)(void *),

                      QEMUTimerCB * write_timer_cb,

> +                   void *timer_opaque)
> +{
> +    memset(ts, 0, sizeof(ThrottleState));
> +
> +    ts->clock = clock;
> +    ts->timers[0] = qemu_new_timer_ns(ts->clock, read_timer, timer_opaque);
> +    ts->timers[1] = qemu_new_timer_ns(ts->clock, write_timer, timer_opaque);
> +}
> +
> +/* destroy a timer */
> +static void throttle_timer_destroy(QEMUTimer **timer)
> +{
> +    assert(*timer != NULL);
> +
> +    if (qemu_timer_pending(*timer)) {
> +        qemu_del_timer(*timer);
> +    }
> +
> +    qemu_free_timer(*timer);
> +    *timer = NULL;
> +}
> +
> +/* To be called last on the ThrottleState */
> +void throttle_destroy(ThrottleState *ts)
> +{
> +    int i;
> +
> +    for (i = 0; i < 2; i++) {
> +        throttle_timer_destroy(&ts->timers[i]);
> +    }
> +}
> +
> +/* is any throttling timer configured */
> +bool throttle_have_timer(ThrottleState *ts)
> +{
> +    if (ts->timers[0]) {
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
> +/* Does any throttling must be done
> + *
> + * @cfg: the throttling configuration to inspect
> + * @ret: true if throttling must be done else false
> + */
> +bool throttle_enabled(ThrottleConfig *cfg)
> +{
> +    int i;
> +
> +    for (i = 0; i < BUCKETS_COUNT; i++) {
> +        if (cfg->buckets[i].ups > 0) {
> +            return true;
> +        }
> +    }
> +
> +    return false;
> +}
> +
> +/* return true if any two throttling parameters conflicts
> + *
> + * @cfg: the throttling configuration to inspect
> + * @ret: true if any conflict detected else false
> + */
> +bool throttle_conflicting(ThrottleConfig *cfg)
> +{
> +    bool bps_flag, ops_flag;
> +    bool bps_max_flag, ops_max_flag;
> +
> +    bps_flag = cfg->buckets[THROTTLE_BPS_TOTAL].ups &&
> +               (cfg->buckets[THROTTLE_BPS_READ].ups ||
> +                cfg->buckets[THROTTLE_BPS_WRITE].ups);
> +
> +    ops_flag = cfg->buckets[THROTTLE_OPS_TOTAL].ups &&
> +               (cfg->buckets[THROTTLE_OPS_READ].ups ||
> +                cfg->buckets[THROTTLE_OPS_WRITE].ups);
> +
> +    bps_max_flag = cfg->buckets[THROTTLE_BPS_TOTAL].max &&
> +                  (cfg->buckets[THROTTLE_BPS_READ].max  ||
> +                   cfg->buckets[THROTTLE_BPS_WRITE].max);
> +
> +    ops_max_flag = cfg->buckets[THROTTLE_OPS_TOTAL].max &&
> +                   (cfg->buckets[THROTTLE_OPS_READ].max ||
> +                   cfg->buckets[THROTTLE_OPS_WRITE].max);
> +
> +    return bps_flag || ops_flag || bps_max_flag || ops_max_flag;
> +}
> +
> +/* check if a throttling configuration is valid
> + * @cfg: the throttling configuration to inspect
> + * @ret: true if valid else false
> + */
> +bool throttle_is_valid(ThrottleConfig *cfg)
> +{
> +    bool invalid = false;
> +    int i;
> +
> +    for (i = 0; i < BUCKETS_COUNT; i++) {
> +        if (cfg->buckets[i].ups < 0) {
> +            invalid = true;
> +        }
> +    }
> +
> +    for (i = 0; i < BUCKETS_COUNT; i++) {
> +        if (cfg->buckets[i].max < 0) {
> +            invalid = true;
> +        }
> +    }
> +
> +    return !invalid;
> +}
> +
> +/* fix bucket parameters */
> +static void throttle_fix_bucket(LeakyBucket *bkt)
> +{
> +    double min = bkt->ups / 10;
> +    /* zero bucket level */
> +    bkt->bucket = 0;
> +
> +    /* take care of not using cpu and also improve throttling precision */
> +    if (bkt->ups &&
> +        bkt->max < min) {
> +        bkt->max = min;
> +    }
> +}
> +
> +/* take care of canceling a timer */
> +static void throttle_cancel_timer(QEMUTimer *timer)
> +{
> +    assert(timer != NULL);
> +    if (!qemu_timer_pending(timer)) {
> +        return;
> +    }
> +
> +    qemu_del_timer(timer);
> +}
> +
> +/* Used to configure the throttle
> + *
> + * @ts: the throttle state we are working on
> + * @cfg: the config to set
> + */
> +void throttle_config(ThrottleState *ts, ThrottleConfig *cfg)
> +{
> +    int i;
> +
> +    ts->cfg = *cfg;
> +
> +    for (i = 0; i < BUCKETS_COUNT; i++) {
> +        throttle_fix_bucket(&ts->cfg.buckets[i]);
> +    }
> +
> +    ts->previous_leak = qemu_get_clock_ns(ts->clock);
> +
> +    for (i = 0; i < 2; i++) {
> +        throttle_cancel_timer(ts->timers[i]);
> +    }
> +}
> +
> +/* used to get config
> + *
> + * @ts: the throttle state we are working on
> + * @cfg: where to write the config
> + */
> +void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
> +{
> +    *cfg = ts->cfg;

Any reason to copy the structure, instead of using the reference?

> +}
> +
> +
> +/* compute if an operation must be allowed and set a timer if not
> + *
> + * NOTE: this function is not unit tested due to it's usage of qemu_mod_timer
> + *
> + * @is_write: the type of operation (read/write)
> + * @ret:      true if the operation is allowed to flow else if must wait
> + */
> +bool throttle_allowed(ThrottleState *ts, bool is_write)

The function name sounds like a immutable check operation, but it actually
reschedules timer. This is not a good style.

> +{
> +    int64_t now = qemu_get_clock_ns(ts->clock);
> +    int64_t next_timer;
> +    bool must_wait;
> +
> +    must_wait = throttle_compute_timer(ts,
> +                                       is_write,
> +                                       now,
> +                                       &next_timer);
> +
> +    /* if the request is throttled arm timer */
> +    if (must_wait) {
> +        qemu_mod_timer(ts->timers[is_write], next_timer);
> +    }
> +
> +    return !must_wait;
> +}
> +
> +/* do the accounting for this operation
> + *
> + * @is_write: the type of operation (read/write)
> + * size:      the size of the operation
> + */
> +void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
> +{
> +    double bytes_size;
> +
> +    /* if cfg.op_size is not defined we will acccount exactly 1 operation */
> +    double units = 1.0;
> +    if (ts->cfg.op_size) {
> +        units = (double) size / ts->cfg.op_size;
> +    }
> +
> +    bytes_size = size * ts->cfg.unit_size;
> +
> +    ts->cfg.buckets[THROTTLE_BPS_TOTAL].bucket += bytes_size;
> +    ts->cfg.buckets[THROTTLE_OPS_TOTAL].bucket += units;
> +
> +    if (is_write) {
> +        ts->cfg.buckets[THROTTLE_BPS_WRITE].bucket += bytes_size;
> +        ts->cfg.buckets[THROTTLE_OPS_WRITE].bucket += units;
> +    } else {
> +        ts->cfg.buckets[THROTTLE_BPS_READ].bucket += bytes_size;
> +        ts->cfg.buckets[THROTTLE_OPS_READ].bucket += units;
> +    }
> +}
> +
> -- 
> 1.7.10.4
> 
>