linux-kernel - Re: [PATCH v4 1/2] sched/fair: Check a task has a fitting cpu when updating misfit

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Date: Sun, 28 Jan 2024 23:32:58 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	linux-kernel@...r.kernel.org,
	Pierre Gondois <Pierre.Gondois@....com>
Subject: Re: [PATCH v4 1/2] sched/fair: Check a task has a fitting cpu when
 updating misfit

On 01/26/24 15:15, Vincent Guittot wrote:

> > > TBH, I don't know. I would need time to think about this...
> > > May be when we set the new affinity of the task
> >
> > I was thinking to actually call update_misfit_status() from another less
> > expensive location.
> >
> > We can certainly do something to help the check less expensive if we must do it
> > in pick_next_task(). For example set a flag if the task belongs to a single
> > capacity value; and store the highest capacity its affinity belongs too. But
> > with cpuset v1, v2 and hotplug I am wary that might get messy.
> 
> I think it worth looking at such solution as this would mean parsing
> the possible max capacity for the task only once per affinity change

Okay. It might not be that bad and just need to do the parsing when we update
the cpus_ptr, which seems to happen only in set_cpus_allowed_common(). I think
I can create a wrapper for fair where we do set_cpus_allowed_common() then do
the checks to discover the max_allowed_capacity and whether the new affinity is
asymmetric or not.


Cheers

--
Qais Yousef