From: Tao Cui <cui.tao@linux.dev>
To: Jens Axboe <axboe@kernel.dk>
Cc: Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>,
Omar Sandoval <osandov@fb.com>,
Bart Van Assche <bvanassche@acm.org>, Yu Kuai <yukuai@fygo.io>,
Chaitanya Kulkarni <kch@nvidia.com>,
Hannes Reinecke <hare@kernel.org>, Ming Lei <ming.lei@redhat.com>,
Damien Le Moal <dlemoal@kernel.org>,
Nilay Shroff <nilay@linux.ibm.com>,
linux-block@vger.kernel.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, cui.tao@linux.dev,
cuitao@kylinos.cn
Subject: [PATCH 3/4] block/blk-iocost: collect per-cpu latency stats over possible CPUs
Date: Mon, 20 Jul 2026 17:37:25 +0800 [thread overview]
Message-ID: <20260720093726.28965-4-cui.tao@linux.dev> (raw)
In-Reply-To: <20260720093726.28965-1-cui.tao@linux.dev>
From: Tao Cui <cuitao@kylinos.cn>
ioc_lat_stat() walks ioc->pcpu_stat with for_each_online_cpu() to
compute missed-ppm and rq_wait deltas. An offlined CPU is skipped, so
its delta is dropped from the period and its last_* watermark is not
advanced; on re-online the next collection sees a delta spanning the
whole offline interval, corrupting the latency/vrate picture.
Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
block/blk-iocost.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 8b2aeba2e1e3..b60625613e09 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1592,7 +1592,7 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
u64 rq_wait_ns = 0;
int cpu, rw;
- for_each_online_cpu(cpu) {
+ for_each_possible_cpu(cpu) {
struct ioc_pcpu_stat *stat = per_cpu_ptr(ioc->pcpu_stat, cpu);
u64 this_rq_wait_ns;
--
2.43.0
next prev parent reply other threads:[~2026-07-20 9:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 9:37 [PATCH 0/4] block: drain per-cpu latency stats over possible CPUs Tao Cui
2026-07-20 9:37 ` [PATCH 1/4] block/blk-stat: drain per-cpu callback " Tao Cui
2026-07-20 9:37 ` [PATCH 2/4] block/blk-iolatency: account per-cpu latency " Tao Cui
2026-07-20 9:37 ` Tao Cui [this message]
2026-07-20 9:37 ` [PATCH 4/4] block/kyber-iosched: flush per-cpu latency buckets " Tao Cui
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