From: no-reply@sashiko.virtuozzo.com
To: Konstantin Khorenko <khorenko@virtuozzo.com>,
Vasileios Almpanis <vasileios.almpanis@virtuozzo.com>,
Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: devel@openvz.org
Subject: Re: [Devel] [PATCH hci-8.1 2/4] sched: keep cfs_rq::nr_iowait balanced for throttled and class changing tasks
Date: Wed, 14 Oct 2026 11:24:27 +0000 [thread overview]
Message-ID: <010701a13a28131c-4e798c6b-bf2b-413e-9f3d-b7916d4962e5-000000@eu-central-1.amazonses.com> (raw)
In-Reply-To: <20261014-ct-iowait-v1-2-9d65fe37cf89@virtuozzo.com>
> Two more paths break the cfs_rq::nr_iowait pairing:
>
> - A throttled task can go to sleep in iowait before it returns to
> user space, e.g. in blkcg_maybe_throttle_current().
> dequeue_throttled_task() doesn't increment the counter but the
> wakeup decrements it, so it wraps around.
> - A sleeping iowait task can change its class through
> sched_setscheduler() or rt_mutex_setprio(). Fair to RT leaves the
> counter incremented forever, RT to fair decrements it without an
> increment.
>
> A CT with both CPU and IO limits hits the first one.
>
> Fix it by incrementing the counter in dequeue_throttled_task() and by
> moving the task between the class counters in check_class_changed(),
> like sched_move_task() does for a cgroup change.
>
> https://virtuozzo.atlassian.net/browse/VSTOR-147823
> Fixes: 415fe063c53e ("sched: Account cfs_rq::nr_iowait")
> Signed-off-by: Vasileios Almpanis <vasileios.almpanis@virtuozzo.com>
Sashiko has reviewed this patch and found no issues. It looks great!
--
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261014-ct-iowait-v1-0-9d65fe37cf89@virtuozzo.com?part=2
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next prev parent reply other threads:[~2026-10-14 11:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-14 11:16 [Devel] [PATCH hci-8.1 0/4] sched: restore Container iowait accounting Vasileios Almpanis
2026-10-14 11:16 ` [Devel] [PATCH hci-8.1 1/4] sched: fix cfs_rq::nr_iowait leak on the remote wakeup path Vasileios Almpanis
2026-10-14 11:23 ` no-reply
2026-10-14 11:16 ` [Devel] [PATCH hci-8.1 2/4] sched: keep cfs_rq::nr_iowait balanced for throttled and class changing tasks Vasileios Almpanis
2026-10-14 11:24 ` no-reply [this message]
2026-10-14 11:16 ` [Devel] [PATCH hci-8.1 3/4] sched: account sleep and block time of a task group entity Vasileios Almpanis
2026-10-14 11:28 ` no-reply
2026-10-14 11:36 ` Vasileios Almpanis
2026-10-14 11:16 ` [Devel] [PATCH hci-8.1 4/4] sched: switch a sleeping task group entity between idle and iowait Vasileios Almpanis
2026-10-14 11:27 ` no-reply
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