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Date: Tue, 14 Nov 2017 14:06:57 -0800
From: Shaohua Li <shli@...nel.org>
To: Tejun Heo <tj@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
kernel-team@...com
Subject: Re: [PATCH 2/2] blk-throtl: add relative percentage support to
latency=
On Thu, Nov 09, 2017 at 02:20:00PM -0800, Tejun Heo wrote:
> This patch updates latency= handling so that the latency target can
> also be specified as a percentage. This allows, in addition to the
> default absolute latency target, to specify the latency target as a
> percentage of the baseline (say, 120% of the expected latency).
>
> A given blkg can only have either absolute or percentage latency
> target. The propgation is updated so that we always consider both
> targets and follow whatever is the least protecting on the path to the
> root.
>
> The percentage latency target is specified and presented with the '%'
> suffix.
>
> $ echo 8:16 rbps=$((100<<20)) riops=100 wbps=$((100<<20)) wiops=100 \
> idle=$((1000*1000)) latency=120% > io.low
> $ cat io.low
> 8:16 rbps=104857600 wbps=104857600 riops=100 wiops=100 idle=1000000 latency=120%
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Shaohua Li <shli@...nel.org>
Reviewed-by: Shaohua Li <shli@...nel.org>
> ---
> block/blk-throttle.c | 66 +++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 51 insertions(+), 15 deletions(-)
>
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -27,6 +27,7 @@ static int throtl_quantum = 32;
> #define MIN_THROTL_BPS (320 * 1024)
> #define MIN_THROTL_IOPS (10)
> #define DFL_LATENCY_TARGET (-1L)
> +#define DFL_LATENCY_TARGET_PCT (-1L)
> #define DFL_IDLE_THRESHOLD (0)
> #define DFL_HD_BASELINE_LATENCY (4000L) /* 4ms */
> #define LATENCY_FILTERED_SSD (0)
> @@ -164,8 +165,11 @@ struct throtl_grp {
>
> unsigned long last_check_time;
>
> + /* Either both target and target_pct are DFL or neither is */
> unsigned long latency_target; /* us */
> unsigned long latency_target_conf; /* us */
> + unsigned long latency_target_pct; /* % */
> + unsigned long latency_target_pct_conf; /* % */
> /* When did we start a new slice */
> unsigned long slice_start[2];
> unsigned long slice_end[2];
> @@ -511,6 +515,8 @@ static struct blkg_policy_data *throtl_p
>
> tg->latency_target = DFL_LATENCY_TARGET;
> tg->latency_target_conf = DFL_LATENCY_TARGET;
> + tg->latency_target_pct = DFL_LATENCY_TARGET_PCT;
> + tg->latency_target_pct_conf = DFL_LATENCY_TARGET_PCT;
> tg->idletime_threshold = DFL_IDLE_THRESHOLD;
> tg->idletime_threshold_conf = DFL_IDLE_THRESHOLD;
>
> @@ -1417,6 +1423,8 @@ static void tg_conf_updated(struct throt
> parent_tg->idletime_threshold);
> this_tg->latency_target = max(this_tg->latency_target,
> parent_tg->latency_target);
> + this_tg->latency_target_pct = max(this_tg->latency_target_pct,
> + parent_tg->latency_target_pct);
> }
>
> /*
> @@ -1528,7 +1536,7 @@ static u64 tg_prfill_limit(struct seq_fi
> u64 bps_dft;
> unsigned int iops_dft;
> char idle_time[26] = "";
> - char latency_time[26] = "";
> + char latency_time[27] = ""; /* +1 for the optional '%' */
>
> if (!dname)
> return 0;
> @@ -1569,8 +1577,11 @@ static u64 tg_prfill_limit(struct seq_fi
> snprintf(idle_time, sizeof(idle_time), " idle=%lu",
> tg->idletime_threshold_conf);
>
> - if (tg->latency_target_conf == ULONG_MAX)
> + if (tg->latency_target_conf == DFL_LATENCY_TARGET)
> strcpy(latency_time, " latency=max");
> + else if (tg->latency_target_pct_conf)
> + snprintf(latency_time, sizeof(latency_time),
> + " latency=%lu%%", tg->latency_target_pct_conf);
> else
> snprintf(latency_time, sizeof(latency_time),
> " latency=%lu", tg->latency_target_conf);
> @@ -1597,7 +1608,7 @@ static ssize_t tg_set_limit(struct kernf
> struct throtl_grp *tg;
> u64 v[4];
> unsigned long idle_time;
> - unsigned long latency_time;
> + unsigned long latency_time, latency_pct;
> int ret;
> int index = of_cft(of)->private;
>
> @@ -1614,8 +1625,10 @@ static ssize_t tg_set_limit(struct kernf
>
> idle_time = tg->idletime_threshold_conf;
> latency_time = tg->latency_target_conf;
> + latency_pct = tg->latency_target_pct_conf;
> while (true) {
> char tok[27]; /* wiops=18446744073709551616 */
> + char is_pct = 0;
> char *p;
> u64 val = U64_MAX;
> int len;
> @@ -1629,7 +1642,11 @@ static ssize_t tg_set_limit(struct kernf
> ret = -EINVAL;
> p = tok;
> strsep(&p, "=");
> - if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
> + if (!p || (sscanf(p, "%llu%c", &val, &is_pct) < 1 &&
> + strcmp(p, "max")))
> + goto out_finish;
> +
> + if (is_pct && (is_pct != '%' || strcmp(tok, "latency")))
> goto out_finish;
>
> ret = -ERANGE;
> @@ -1637,20 +1654,33 @@ static ssize_t tg_set_limit(struct kernf
> goto out_finish;
>
> ret = -EINVAL;
> - if (!strcmp(tok, "rbps"))
> + if (!strcmp(tok, "rbps")) {
> v[0] = val;
> - else if (!strcmp(tok, "wbps"))
> + } else if (!strcmp(tok, "wbps")) {
> v[1] = val;
> - else if (!strcmp(tok, "riops"))
> + } else if (!strcmp(tok, "riops")) {
> v[2] = min_t(u64, val, UINT_MAX);
> - else if (!strcmp(tok, "wiops"))
> + } else if (!strcmp(tok, "wiops")) {
> v[3] = min_t(u64, val, UINT_MAX);
> - else if (off == LIMIT_LOW && !strcmp(tok, "idle"))
> + } else if (off == LIMIT_LOW && !strcmp(tok, "idle")) {
> idle_time = val;
> - else if (off == LIMIT_LOW && !strcmp(tok, "latency"))
> - latency_time = val;
> - else
> + } else if (off == LIMIT_LOW && !strcmp(tok, "latency")) {
> + /* gonna use max of the two, set the other one to 0 */
> + if (val != U64_MAX) {
> + if (is_pct) {
> + latency_time = 0;
> + latency_pct = val;
> + } else {
> + latency_time = val;
> + latency_pct = 0;
> + }
> + } else {
> + latency_time = DFL_LATENCY_TARGET;
> + latency_pct = DFL_LATENCY_TARGET_PCT;
> + }
> + } else {
> goto out_finish;
> + }
> }
>
> tg->bps_conf[READ][index] = v[0];
> @@ -1674,6 +1704,7 @@ static ssize_t tg_set_limit(struct kernf
> tg->iops_conf[WRITE][LIMIT_MAX]);
> tg->idletime_threshold_conf = idle_time;
> tg->latency_target_conf = latency_time;
> + tg->latency_target_pct_conf = latency_pct;
>
> /* force user to configure all settings for low limit */
> if (!(tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW] ||
> @@ -1686,9 +1717,11 @@ static ssize_t tg_set_limit(struct kernf
> tg->iops[WRITE][LIMIT_LOW] = 0;
> tg->idletime_threshold = DFL_IDLE_THRESHOLD;
> tg->latency_target = DFL_LATENCY_TARGET;
> + tg->latency_target_pct = DFL_LATENCY_TARGET_PCT;
> } else if (index == LIMIT_LOW) {
> tg->idletime_threshold = tg->idletime_threshold_conf;
> tg->latency_target = tg->latency_target_conf;
> + tg->latency_target_pct = tg->latency_target_pct_conf;
> }
>
> blk_throtl_update_limit_valid(tg->td);
> @@ -1799,7 +1832,7 @@ static bool throtl_tg_is_idle(struct thr
> tg->idletime_threshold == DFL_IDLE_THRESHOLD ||
> (ktime_get_ns() >> 10) - tg->last_finish_time > time ||
> tg->avg_idletime > tg->idletime_threshold ||
> - (tg->latency_target && tg->bio_cnt &&
> + ((tg->latency_target || tg->latency_target_pct) && tg->bio_cnt &&
> tg->bad_bio_cnt * 5 < tg->bio_cnt);
> throtl_log(&tg->service_queue,
> "avg_idle=%ld, idle_threshold=%ld, bad_bio=%d, total_bio=%d, is_idle=%d, scale=%d",
> @@ -2293,13 +2326,16 @@ void blk_throtl_bio_endio(struct bio *bi
> throtl_track_latency(tg->td, blk_stat_size(&bio->bi_issue_stat),
> bio_op(bio), lat);
>
> - if (tg->latency_target && lat >= tg->td->filtered_latency) {
> + if ((tg->latency_target || tg->latency_target_pct) &&
> + lat >= tg->td->filtered_latency) {
> int bucket;
> unsigned int threshold;
>
> bucket = request_bucket_index(
> blk_stat_size(&bio->bi_issue_stat));
> - threshold = tg->latency_target;
> + threshold = max(tg->latency_target,
> + tg->latency_target_pct *
> + tg->td->avg_buckets[bucket].latency / 100);
> if (lat > threshold)
> tg->bad_bio_cnt++;
> /*
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