Re: [PATCH] sched/fair: Fix misuse of available_idle_cpu()

From: Mel Gorman
Date: Thu Sep 08 2022 - 06:36:44 EST

On Thu, Sep 08, 2022 at 04:07:02PM +0800, Abel Wu wrote:
> The function available_idle_cpu() was introduced to distinguish
> between the code paths that cares if the vCPU is preempted and
> the ones don't care. In general, available_idle_cpu() is used in
> selecting cpus for immediate use, e.g. ttwu. While idle_cpu() is
> used in the paths that only cares about the cpu is idle or not,
> and __update_idle_core() is one of them.
> Use idle_cpu() instead in the idle path to make has_idle_core
> a better hint.
> Fixes: 943d355d7fee (sched/core: Distinguish between idle_cpu() calls based on desired effect, introduce available_idle_cpu())
> Signed-off-by: Abel Wu <wuyun.abel@xxxxxxxxxxxxx>

Seems fair. As vCPU preemption is specific to virtualisation, it is very
unlikely that SMT is exposed to the guest so the impact of the patch is
minimal but I still think it's right so;

Acked-by: Mel Gorman <mgorman@xxxxxxx>

Mel Gorman