[PATCH 1/4] block/blk-stat: drain per-cpu callback stats over possible CPUs
Tao Cui <[email protected]>
| Newsgroups | org.kernel.vger.cgroups,org.kernel.vger.linux-block,org.kernel.vger.linux-kernel |
|---|---|
| Message-ID | <[email protected]> |
From: Tao Cui <[email protected]> blk_stat_timer_fn() sums and resets a callback's per-cpu buckets using for_each_online_cpu(). A CPU that goes offline with pending samples is skipped, so its samples are neither accumulated into the window nor cleared; they sit in the bucket until the CPU comes back online, at which point the stale values are flushed into whatever window is then running. This silently corrupts the latency picture that consumers (notably writeback throttling via wbt, and blk-mq latency tracking) base decisions on around CPU hotplug: under-counting while the CPU is offline, then a burst of stale data on re-online. Fixes: 34dbad5d26e2 ("blk-stat: convert to callback-based statistics reporting") Signed-off-by: Tao Cui <[email protected]> --- block/blk-stat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/blk-stat.c b/block/blk-stat.c index de126e1ea5ac..d57c2fc6bf06 100644 --- a/block/blk-stat.c +++ b/block/blk-stat.c @@ -83,7 +83,7 @@ static void blk_stat_timer_fn(struct timer_list *t) for (bucket = 0; bucket < cb->buckets; bucket++) blk_rq_stat_init(&cb->stat[bucket]); - for_each_online_cpu(cpu) { + for_each_possible_cpu(cpu) { struct blk_rq_stat *cpu_stat; cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu); -- 2.43.0