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block/blk-iolatency: account per-cpu latency stats over possible CPUs

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iolatency_check_latencies() and iolatency_ssd_stat() iterate a blkg's
per-cpu latency stats with for_each_online_cpu().  When a CPU that has
accumulated io.latency samples goes offline, its bucket is skipped: the
check loop (which also resets) neither sums nor clears it, and the show
path under-reports.  On re-online the stranded samples are flushed into
a later check window, which can trigger a spurious throttle/scale
adjustment.

Fixes: d706751215 ("block: introduce blk-iolatency io controller")
Fixes: 1fa2840e56 ("blk-iolatency: use a percentile approache for ssd's")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260720093726.28965-3-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tao Cui
2026-08-03 20:03:20 -06:00
committed by Jens Axboe
parent 9d617828cf
commit e0698304bd
1 changed files with 2 additions and 2 deletions
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block/blk-iolatency.c
+2 -2
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@@ -523,7 +523,7 @@ static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
latency_stat_init(iolat, &stat);
preempt_disable();
for_each_online_cpu(cpu) {
for_each_possible_cpu(cpu) {
struct latency_stat *s;
s = per_cpu_ptr(iolat->stats, cpu);
latency_stat_sum(iolat, &stat, s);
@@ -925,7 +925,7 @@ static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
latency_stat_init(iolat, &stat);
preempt_disable();
for_each_online_cpu(cpu) {
for_each_possible_cpu(cpu) {
struct latency_stat *s;
s = per_cpu_ptr(iolat->stats, cpu);
latency_stat_sum(iolat, &stat, s);