linux-kernel - Re: [RFC PATCH] sched: Do not copy user_cpus_ptr when parent is reset_on

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Message-ID: <20240905140902.GB179482@pauld.westford.csb>
Date: Thu, 5 Sep 2024 10:09:02 -0400
From: Phil Auld <pauld@...hat.com>
To: Waiman Long <longman@...hat.com>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, mingo@...hat.com,
	peterz@...radead.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, linux-kernel@...r.kernel.org,
	ke.wang@...soc.com, di.shen@...soc.com, xuewen.yan94@...il.com
Subject: Re: [RFC PATCH] sched: Do not copy user_cpus_ptr when parent is
 reset_on_fork

On Thu, Sep 05, 2024 at 10:00:36AM -0400 Waiman Long wrote:
> 
> On 9/5/24 09:12, Phil Auld wrote:
> > On Thu, Sep 05, 2024 at 08:42:33AM -0400 Waiman Long wrote:
> > > On 9/5/24 05:04, Xuewen Yan wrote:
> > > > Now, the task's user_cpus_ptr would dup from parent's user_cpus_ptr.
> > > > It is better reset the user_cpus_ptr when parent's reset_on_fork
> > > > is set.
> > > According to sched(7):
> > > 
> > >         Each thread has a reset-on-fork scheduling flag.  When this flag
> > >         is set, children created by fork(2) do not inherit privileged
> > >         scheduling policies.
> > > 
> > > It can be argued what are considered privileged scheduling policies. AFAICS,
> > > a restricted affinity doesn't seem to be a "privileged" scheduling policy.
> > > That is my own opinion strictly from the definition point of view, I will
> > > let others weigh in on that and I am OK to go either way.
> > > 
> > I think that one could argue that clearing a restricted affinity is
> > increasing the privilege and not preventing inheritence of same.
> > i.e. it would be the opposite of what reset-on-fork means.
> > 
> > I'd say NAK to this one if I had that power.
> 
> Maybe I am not clear enough in my previous mail. My position is the same as
> yours. I think this patch is not necessary. More reasons should be provided
> as to why it is right to not inherited the restricted affinity when
> reset-on-fork flag is reset.
>

No, you were clear. I was just providing my opinion, weighing in :)  

Cheers,
Phil

> Cheers,
> Longman
> 

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