Re: [Devel] [PATCH hci-8.1 0/4] sched: restore Container iowait accounting

[Konstantin Khorenko <khorenko@virtuozzo.com>]

On 10/14/26 13:16, Vasileios Almpanis wrote:
> Container iowait is always 0 on vz10, both in cpu.proc.stat and in the
> CT's /proc/stat, so top inside a CT shows 0 wa.
> 
> Two things are broken. cfs_rq::nr_iowait goes out of balance on a few
> paths, and the group entity never gets sleep_start/block_start, so
> neither idle nor iowait is accounted for the group. The counter has to
> be fixed first, otherwise the groups would look blocked forever.
> 
> Patch 1 fixes the nr_iowait leak on the remote wakeup path.
> Patch 2 fixes nr_iowait for throttled and class changing tasks.
> Patch 3 accounts sleep and block time of the group entity.
> Patch 4 switches a sleeping group between idle and iowait.
> 
> The accounting depends on kernel.sched_schedstats=1, same as on vz7.
> 
> Known issues:
>  - If kernel.sched_schedstats is switched off while a group entity has
>    an open sleep or block period, the stamp stays set and cpu.proc.stat
>    keeps adding idle or iowait until the group is enqueued again, even
>    after schedstats are back on. This can be fixed separately by
>    clearing the stamps in set_schedstats().
>  - cfs_rq::nr_iowait is not hierarchical, so a CT that runs its IO in
>    nested cpu cgroups shows it as idle.

i have pushed the patchset, it looks ok.

But i really think we better address both known issues mentioned above in a separate series (or several series),
i think they are important.

+ can you please also write a selftest for this functionality?


> 
> Tested on a vz10 node with direct IO reads in a CT, with CPU and IO
> limits, and with class switches, cgroup moves and affinity changes
> during IO. fio shows no difference against the base kernel.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-147823
> 
> Signed-off-by: Vasileios Almpanis <vasileios.almpanis@virtuozzo.com>
> ---
> Vasileios Almpanis (4):
>       sched: fix cfs_rq::nr_iowait leak on the remote wakeup path
>       sched: keep cfs_rq::nr_iowait balanced for throttled and class changing tasks
>       sched: account sleep and block time of a task group entity
>       sched: switch a sleeping task group entity between idle and iowait
> 
>  kernel/sched/core.c  | 35 ++++++++++++++++++-----------
>  kernel/sched/fair.c  | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>  kernel/sched/sched.h | 12 ++++++++++
>  3 files changed, 94 insertions(+), 15 deletions(-)
> ---
> base-commit: defa968cbe8c38f1ff0231042dee07f00d27b2c9
> change-id: 20261013-ct-iowait-d8e9a32b8135
> 

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