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SubjectRe: [RFC PATCH] blk-throttle: add burst allowance.
On Tue, Nov 14, 2017 at 03:10:22PM -0800, Khazhismel Kumykov wrote:
> Allows configuration additional bytes or ios before a throttle is
> triggered.
>
> This allows implementation of a bucket style rate-limit/throttle on a
> block device. Previously, bursting to a device was limited to allowance
> granted in a single throtl_slice (similar to a bucket with limit N and
> refill rate N/slice).
>
> Additional parameters bytes/io_burst_conf defined for tg, which define a
> number of bytes/ios that must be depleted before throttling happens. A
> tg that does not deplete this allowance functions as though it has no
> configured limits. tgs earn additional allowance at rate defined by
> bps/iops for the tg. Once a tg has *_disp > *_burst_conf, throttling
> kicks in. If a tg is idle for a while, it will again have some burst
> allowance before it gets throttled again.
>
> slice_end for a tg is extended until io_disp/byte_disp would fall to 0,
> when all "used" burst allowance would be earned back. trim_slice still
> does progress slice_start as before and decrements *_disp as before, and
> tgs continue to get bytes/ios in throtl_slice intervals.

Can you describe why we need this? It would be great if you can describe the
usage model and an example. Does this work for io.low/io.max or both?

Thanks,
Shaohua

> Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
> ---
> block/Kconfig | 11 +++
> block/blk-throttle.c | 192 +++++++++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 189 insertions(+), 14 deletions(-)
>
> diff --git a/block/Kconfig b/block/Kconfig
> index 28ec55752b68..fbd05b419f93 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -128,6 +128,17 @@ config BLK_DEV_THROTTLING_LOW
>
> Note, this is an experimental interface and could be changed someday.
>
> +config BLK_DEV_THROTTLING_BURST
> + bool "Block throttling .burst allowance interface"
> + depends on BLK_DEV_THROTTLING
> + default n
> + ---help---
> + Add .burst allowance for block throttling. Burst allowance allows for
> + additional unthrottled usage, while still limiting speed for sustained
> + usage.
> +
> + If in doubt, say N.
> +
> config BLK_CMDLINE_PARSER
> bool "Block device command line partition parser"
> default n
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 96ad32623427..27c084312772 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -157,6 +157,11 @@ struct throtl_grp {
> /* Number of bio's dispatched in current slice */
> unsigned int io_disp[2];
>
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> + uint64_t bytes_burst_conf[2];
> + unsigned int io_burst_conf[2];
> +#endif
> +
> unsigned long last_low_overflow_time[2];
>
> uint64_t last_bytes_disp[2];
> @@ -507,6 +512,12 @@ static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
> tg->bps_conf[WRITE][LIMIT_MAX] = U64_MAX;
> tg->iops_conf[READ][LIMIT_MAX] = UINT_MAX;
> tg->iops_conf[WRITE][LIMIT_MAX] = UINT_MAX;
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> + tg->bytes_burst_conf[READ] = 0;
> + tg->bytes_burst_conf[WRITE] = 0;
> + tg->io_burst_conf[READ] = 0;
> + tg->io_burst_conf[WRITE] = 0;
> +#endif
> /* LIMIT_LOW will have default value 0 */
>
> tg->latency_target = DFL_LATENCY_TARGET;
> @@ -800,6 +811,26 @@ static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
> tg->slice_end[rw], jiffies);
> }
>
> +/*
> + * When current slice should end.
> + *
> + * With CONFIG_BLK_DEV_THROTTLING_BURST, we will wait longer than min_wait
> + * for slice to recover used burst allowance. (*_disp -> 0). Setting slice_end
> + * before this would result in tg receiving additional burst allowance.
> + */
> +static inline unsigned long throtl_slice_wait(struct throtl_grp *tg, bool rw,
> + unsigned long min_wait)
> +{
> + unsigned long bytes_wait = 0, io_wait = 0;
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> + if (tg->bytes_burst_conf[rw])
> + bytes_wait = (tg->bytes_disp[rw] * HZ) / tg_bps_limit(tg, rw);
> + if (tg->io_burst_conf[rw])
> + io_wait = (tg->io_disp[rw] * HZ) / tg_iops_limit(tg, rw);
> +#endif
> + return max(min_wait, max(bytes_wait, io_wait));
> +}
> +
> static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
> unsigned long jiffy_end)
> {
> @@ -849,7 +880,8 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
> * is bad because it does not allow new slice to start.
> */
>
> - throtl_set_slice_end(tg, rw, jiffies + tg->td->throtl_slice);
> + throtl_set_slice_end(tg, rw,
> + jiffies + throtl_slice_wait(tg, rw, tg->td->throtl_slice));
>
> time_elapsed = jiffies - tg->slice_start[rw];
>
> @@ -889,7 +921,7 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
> unsigned long *wait)
> {
> bool rw = bio_data_dir(bio);
> - unsigned int io_allowed;
> + unsigned int io_allowed, io_disp;
> unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
> u64 tmp;
>
> @@ -908,6 +940,17 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
> * have been trimmed.
> */
>
> + io_disp = tg->io_disp[rw];
> +
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> + if (tg->io_disp[rw] < tg->io_burst_conf[rw]) {
> + if (wait)
> + *wait = 0;
> + return true;
> + }
> + io_disp -= tg->io_burst_conf[rw];
> +#endif
> +
> tmp = (u64)tg_iops_limit(tg, rw) * jiffy_elapsed_rnd;
> do_div(tmp, HZ);
>
> @@ -916,14 +959,14 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
> else
> io_allowed = tmp;
>
> - if (tg->io_disp[rw] + 1 <= io_allowed) {
> + if (io_disp + 1 <= io_allowed) {
> if (wait)
> *wait = 0;
> return true;
> }
>
> /* Calc approx time to dispatch */
> - jiffy_wait = ((tg->io_disp[rw] + 1) * HZ) / tg_iops_limit(tg, rw) + 1;
> + jiffy_wait = ((io_disp + 1) * HZ) / tg_iops_limit(tg, rw) + 1;
>
> if (jiffy_wait > jiffy_elapsed)
> jiffy_wait = jiffy_wait - jiffy_elapsed;
> @@ -939,7 +982,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
> unsigned long *wait)
> {
> bool rw = bio_data_dir(bio);
> - u64 bytes_allowed, extra_bytes, tmp;
> + u64 bytes_allowed, extra_bytes, bytes_disp, tmp;
> unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
> unsigned int bio_size = throtl_bio_data_size(bio);
>
> @@ -951,18 +994,28 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
>
> jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
>
> + bytes_disp = tg->bytes_disp[rw];
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> + if (tg->bytes_disp[rw] < tg->bytes_burst_conf[rw]) {
> + if (wait)
> + *wait = 0;
> + return true;
> + }
> + bytes_disp -= tg->bytes_burst_conf[rw];
> +#endif
> +
> tmp = tg_bps_limit(tg, rw) * jiffy_elapsed_rnd;
> do_div(tmp, HZ);
> bytes_allowed = tmp;
>
> - if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) {
> + if (bytes_disp + bio_size <= bytes_allowed) {
> if (wait)
> *wait = 0;
> return true;
> }
>
> /* Calc approx time to dispatch */
> - extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
> + extra_bytes = bytes_disp + bio_size - bytes_allowed;
> jiffy_wait = div64_u64(extra_bytes * HZ, tg_bps_limit(tg, rw));
>
> if (!jiffy_wait)
> @@ -986,7 +1039,7 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
> unsigned long *wait)
> {
> bool rw = bio_data_dir(bio);
> - unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
> + unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0, disp_time;
>
> /*
> * Currently whole state machine of group depends on first bio
> @@ -1015,10 +1068,10 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
> if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
> throtl_start_new_slice(tg, rw);
> else {
> - if (time_before(tg->slice_end[rw],
> - jiffies + tg->td->throtl_slice))
> - throtl_extend_slice(tg, rw,
> - jiffies + tg->td->throtl_slice);
> + disp_time = jiffies + throtl_slice_wait(
> + tg, rw, tg->td->throtl_slice);
> + if (time_before(tg->slice_end[rw], disp_time))
> + throtl_extend_slice(tg, rw, disp_time);
> }
>
> if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
> @@ -1033,8 +1086,9 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
> if (wait)
> *wait = max_wait;
>
> - if (time_before(tg->slice_end[rw], jiffies + max_wait))
> - throtl_extend_slice(tg, rw, jiffies + max_wait);
> + disp_time = jiffies + throtl_slice_wait(tg, rw, max_wait);
> + if (time_before(tg->slice_end[rw], disp_time))
> + throtl_extend_slice(tg, rw, disp_time);
>
> return 0;
> }
> @@ -1705,6 +1759,108 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
> return ret ?: nbytes;
> }
>
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> +static u64 tg_prfill_burst(struct seq_file *sf, struct blkg_policy_data *pd,
> + int data)
> +{
> + struct throtl_grp *tg = pd_to_tg(pd);
> + const char *dname = blkg_dev_name(pd->blkg);
> + char bufs[4][21];
> +
> + if (!dname)
> + return 0;
> +
> + if (tg->bytes_burst_conf[READ] == 0 &&
> + tg->bytes_burst_conf[WRITE] == 0 &&
> + tg->io_burst_conf[READ] == 0 &&
> + tg->io_burst_conf[WRITE] == 0)
> + return 0;
> +
> + snprintf(bufs[0], sizeof(bufs[0]), "%llu",
> + tg->bytes_burst_conf[READ]);
> + snprintf(bufs[1], sizeof(bufs[1]), "%llu",
> + tg->bytes_burst_conf[WRITE]);
> + snprintf(bufs[2], sizeof(bufs[2]), "%u",
> + tg->io_burst_conf[READ]);
> + snprintf(bufs[3], sizeof(bufs[3]), "%u",
> + tg->io_burst_conf[WRITE]);
> +
> + seq_printf(sf, "%s brbyte=%s bwbyte=%s brio=%s bwio=%s\n",
> + dname, bufs[0], bufs[1], bufs[2], bufs[3]);
> + return 0;
> +}
> +
> +static int tg_print_burst(struct seq_file *sf, void *v)
> +{
> + blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_burst,
> + &blkcg_policy_throtl, 0, false);
> + return 0;
> +}
> +
> +static ssize_t tg_set_burst(struct kernfs_open_file *of,
> + char *buf, size_t nbytes, loff_t off)
> +{
> + struct blkcg *blkcg = css_to_blkcg(of_css(of));
> + struct blkg_conf_ctx ctx;
> + struct throtl_grp *tg;
> + u64 v[4];
> + int ret;
> +
> + ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
> + if (ret)
> + return ret;
> +
> + tg = blkg_to_tg(ctx.blkg);
> +
> + v[0] = tg->bytes_burst_conf[READ];
> + v[1] = tg->bytes_burst_conf[WRITE];
> + v[2] = tg->io_burst_conf[READ];
> + v[3] = tg->io_burst_conf[WRITE];
> +
> + while (true) {
> + char tok[28]; /* bwbyte=18446744073709551616 */
> + char *p;
> + u64 val = U64_MAX;
> + int len;
> +
> + if (sscanf(ctx.body, "%27s%n", tok, &len) != 1)
> + break;
> + if (tok[0] == '\0')
> + break;
> + ctx.body += len;
> +
> + ret = -EINVAL;
> + p = tok;
> + strsep(&p, "=");
> + if (!p || (kstrtoull(p, 0, &val) != 0 && strcmp(p, "max")))
> + goto out_finish;
> +
> + ret = -EINVAL;
> + if (!strcmp(tok, "brbyte"))
> + v[0] = val;
> + else if (!strcmp(tok, "bwbyte"))
> + v[1] = val;
> + else if (!strcmp(tok, "brio"))
> + v[2] = min_t(u64, val, UINT_MAX);
> + else if (!strcmp(tok, "bwio"))
> + v[3] = min_t(u64, val, UINT_MAX);
> + else
> + goto out_finish;
> + }
> +
> + tg->bytes_burst_conf[READ] = v[0];
> + tg->bytes_burst_conf[WRITE] = v[1];
> + tg->io_burst_conf[READ] = v[2];
> + tg->io_burst_conf[WRITE] = v[3];
> +
> + tg_conf_updated(tg, false);
> + ret = 0;
> +out_finish:
> + blkg_conf_finish(&ctx);
> + return ret ?: nbytes;
> +}
> +#endif
> +
> static struct cftype throtl_files[] = {
> #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
> {
> @@ -1714,6 +1870,14 @@ static struct cftype throtl_files[] = {
> .write = tg_set_limit,
> .private = LIMIT_LOW,
> },
> +#endif
> +#ifdef CONFIG_BLK_DEV_THROTTLING_BURST
> + {
> + .name = "burst",
> + .flags = CFTYPE_NOT_ON_ROOT,
> + .seq_show = tg_print_burst,
> + .write = tg_set_burst,
> + },
> #endif
> {
> .name = "max",
> --
> 2.15.0.448.gf294e3d99a-goog
>


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