linux-kernel - [PATCH 0/2] cgroup/cpuset: Task migration optimization

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Message-Id: <20221208195634.2604362-1-longman@redhat.com>
Date:   Thu,  8 Dec 2022 14:56:32 -0500
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 0/2] cgroup/cpuset: Task migration optimization

It is found that workloads that generate a lot of task migrations
among different cpusets are severely throttled because of the use
of percpu rwsem in cpuset_rwsem. It is the same problem that led to
commit 3942a9bd7b58 ("locking, rcu, cgroup: Avoid synchronize_sched()
in __cgroup_procs_write()") and commit 6a010a49b63a ("cgroup: Make
!percpu threadgroup_rwsem operations optional").

The first patch in this series changes cpuset_can_attach() to use
the read lock instead of the write lock. The second patch allows
disabling of percpu reader fast path depending on the presence of
CGRP_ROOT_FAVOR_DYNMODS flag in the cgroup root.

Waiman Long (2):
  cgroup/cpuset: Use cpuset_rwsem read lock in cpuset_can_attach()
  cgroup/cpuset: Make percpu cpuset_rwsem operation depending on DYNMODS
    state

 kernel/cgroup/cpuset.c | 75 ++++++++++++++++++++++++++++++++----------
 1 file changed, 58 insertions(+), 17 deletions(-)

-- 
2.31.1