linux-kernel - [PATCH v6 0/5] sched: Persistent user requested affinity

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Date:   Thu, 25 Aug 2022 21:01:14 -0400
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v6 0/5] sched: Persistent user requested affinity

v6:
 - Drop the cpuset patch and make user_cpus_ptr masking applicable to
   all callers of set_cpus_allowed_ptr().
 - Make user_cpus_ptr and cpus_mask update in a single lock critical
   section to avoid race problems.

v5:
 - Update patch 3 to handle race with concurrent sched_setaffinity()
   by rechecking a previously cleared user_cpus_ptr afterward.

v4:
 - Update patch 1 to make sched_setaffinity() the only function to
   update user_cpus_ptr to make the logic simpler and
   easier to understand. restrict_cpus_allowed_ptr() and
   relax_compatible_cpus_allowed_ptr() will just use it if present.

The user_cpus_ptr field is added by commit b90ca8badbd1 ("sched:
Introduce task_struct::user_cpus_ptr to track requested affinity")
which uses it narrowly to allow keeping cpus affinity intact with
asymmetric cpu setup.

This patchset extends user_cpus_ptr to store user requested cpus affinity
via the sched_setaffinity() API. With that information available, it will
enable cpuset and other callers of set_cpus_allowed_ptr() like hotplug
to keep cpus afinity as close to what the user wants as possible within
the cpu list constraint of the current cpuset. Otherwise some change
to the cpuset hierarchy or a hotplug event may reset the cpumask of
the tasks in the affected cpusets to the default cpuset value even if
those tasks have cpus affinity explicitly set by the users before.

It also means that once sched_setaffinity() is called, user_cpus_ptr
will remain allocated until the task exits.

Waiman Long (5):
  sched: Add __releases annotations to affine_move_task()
  sched: Use user_cpus_ptr for saving user provided cpumask in
    sched_setaffinity()
  sched: Enforce user requested affinity
  sched: Handle set_cpus_allowed_ptr() & sched_setaffinity() race
  sched: Fix sched_setaffinity() and fork/clone() race

 kernel/sched/core.c  | 174 +++++++++++++++++++++++++++----------------
 kernel/sched/sched.h |  11 ++-
 2 files changed, 121 insertions(+), 64 deletions(-)

-- 
2.31.1