From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Will Deacon <will@kernel.org>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v3 1/3] sched: Use user_cpus_ptr for saving user provided cpumask in sched_setaffinity()
Date: Mon, 15 Aug 2022 09:52:27 -0400 [thread overview]
Message-ID: <401bae73-3063-e0ab-c288-2c6e3be75fc5@redhat.com> (raw)
In-Reply-To: <YvoKa3tbOaszsp1y@worktop.programming.kicks-ass.net>
On 8/15/22 04:57, Peter Zijlstra wrote:
> On Fri, Aug 12, 2022 at 04:39:27PM -0400, Waiman Long wrote:
>> The user_cpus_ptr field is added by commit b90ca8badbd1 ("sched:
>> Introduce task_struct::user_cpus_ptr to track requested affinity"). It
>> is currently used only by arm64 arch due to possible asymmetric cpu
>> setup. This patch extends its usage to save user provided cpumask when
>> sched_setaffinity() is called for all arches.
>>
>> To preserve the existing arm64 use case, a new cpus_affinity_set flag is
>> added to differentiate if user_cpus_ptr is set up by sched_setaffinity()
>> or by force_compatible_cpus_allowed_ptr(). user_cpus_ptr
>> set by sched_setaffinity() has priority and won't be
>> overwritten by force_compatible_cpus_allowed_ptr() or
>> relax_compatible_cpus_allowed_ptr().
> What why ?! The only possible case where
> restrict_cpus_allowed_ptr() will now need that weird new state is when
> the affinity has never been set before, in that case cpus_ptr should be
> possible_mask.
Since I don't have a full history for this particular patch series that
add user_cpus_ptr, I am hesitant to change the current behavior for
arm64 systems. However, given the statement that user_cpus_ptr is for
tracking "requested affinity" which I assume is when user applications
call sched_setaffinity(). It does make sense we may not really need this
if sched_setaffinity() is never called.
> Please just make a single consistent rule and don't make weird corner
> cases like this.
I will take a closer look to try to simplify the rule here.
Cheers,
Longman
next prev parent reply other threads:[~2022-08-15 13:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-12 20:39 [PATCH v3 0/3] sched, cgroup/cpuset: Keep user set cpus affinity Waiman Long
2022-08-12 20:39 ` [PATCH v3 1/3] sched: Use user_cpus_ptr for saving user provided cpumask in sched_setaffinity() Waiman Long
2022-08-15 8:57 ` Peter Zijlstra
2022-08-15 13:52 ` Waiman Long [this message]
2022-08-15 14:25 ` Peter Zijlstra
2022-08-15 15:23 ` Waiman Long
2022-08-12 20:39 ` [PATCH v3 2/3] sched: Provide copy_user_cpus_mask() to copy out user mask Waiman Long
2022-08-15 8:58 ` Peter Zijlstra
2022-08-15 13:37 ` Waiman Long
2022-08-12 20:39 ` [PATCH v3 3/3] cgroup/cpuset: Keep user set cpus affinity Waiman Long
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