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SubjectRe: [PATCH v5 5/7] sched/fair: Add sched group latency support
On 09/25/22 16:39, Vincent Guittot wrote:
> Task can set its latency priority with sched_setattr(), which is then used
> to set the latency offset of its sched_entity, but sched group entities
> still have the default latency offset value.
>
> Add a latency.nice field in cpu cgroup controller to set the latency
> priority of the group similarly to sched_setattr(). The latency priority
> is then used to set the offset of the sched_entities of the group.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> Documentation/admin-guide/cgroup-v2.rst | 8 ++++
> kernel/sched/core.c | 53 +++++++++++++++++++++++++
> kernel/sched/fair.c | 33 +++++++++++++++
> kernel/sched/sched.h | 4 ++
> 4 files changed, 98 insertions(+)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index be4a77baf784..d8ae7e411f9c 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1095,6 +1095,14 @@ All time durations are in microseconds.
> values similar to the sched_setattr(2). This maximum utilization
> value is used to clamp the task specific maximum utilization clamp.
>
> + cpu.latency.nice
> + A read-write single value file which exists on non-root
> + cgroups. The default is "0".
> +
> + The nice value is in the range [-20, 19].
> +
> + This interface file allows reading and setting latency using the
> + same values used by sched_setattr(2).

I still don't understand how tasks will inherit the latency_nice value from
cgroups they're attached to.

For example, in EAS path we operate at task level only. If the task's
p->latency_nice = 0, but it belongs to a task group tg->latency_nice = -19;
what should the task's latency_nice be in this case? If it's in a hierarchy,
how would the effective value be calculated?


Thanks

--
Qais Yousef

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