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Date: Thu, 8 Sep 2022 15:17:01 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Mel Gorman <mgorman@...e.de> Cc: Abel Wu <wuyun.abel@...edance.com>, Vincent Guittot <vincent.guittot@...aro.org>, Rohit Jain <rohit.k.jain@...cle.com>, Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] sched/fair: Fix misuse of available_idle_cpu() On Thu, Sep 08, 2022 at 11:36:32AM +0100, Mel Gorman wrote: > 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@...edance.com> > > 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 Right; only pinned guests typically expose such topology information (anything else would be quite broken). > minimal but I still think it's right so; I'm not convinced; all of select_idle_sibling() seems to use available_idle_cpu(), and that's the only consumer of __update_idle_core(), so in that respect the current state makes sense.
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