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From: Tejun Heo <tj@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: "Johannes Weiner" <hannes@cmpxchg.org>,
	"Michal Koutný" <mkoutny@suse.com>,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Chen Ridong" <chenridong@huawei.com>
Subject: Re: [PATCH 2/2] cgroup/cpuset: Change callback_lock to raw_spinlock_t
Date: Mon, 20 Oct 2025 07:00:03 -1000	[thread overview]
Message-ID: <aPZqk4h0ek_QM9o5@slm.duckdns.org> (raw)
In-Reply-To: <20251020023207.177809-3-longman@redhat.com>

On Sun, Oct 19, 2025 at 10:32:07PM -0400, Waiman Long wrote:
> The callback_lock is acquired either to read a stable set of cpu
> or node masks or to modify those masks when cpuset_mutex is also
> acquired. Sometime, it may need to go up the cgroup hierarchy while
> holding the lock to find the right set of masks to use. Assuming that
> the depth of the cgroup hierarch is finite and typically small, the
> lock hold time should be limited.
> 
> As a result, it can be converted to raw_spinlock_t to reduce overhead
> in a PREEMPT_RT setting without introducing excessive latency.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>

Is this something that RT people would like? Why does the overhead of the
lock matter? I think this patch requires more justifications.

Thanks.

-- 
tejun

  reply	other threads:[~2025-10-20 17:00 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-10-20  2:32 [PATCH 0/2] cgroup/cpuset: Miscellaneous cleanup Waiman Long
2025-10-20  2:32 ` [PATCH 1/2] cgroup/cpuset: Don't track # of local child partitions Waiman Long
2025-10-20  6:57   ` Chen Ridong
2025-10-20 17:02     ` Tejun Heo
2025-10-21  2:06       ` Chen Ridong
2025-10-20 17:02   ` Tejun Heo
2025-10-20  2:32 ` [PATCH 2/2] cgroup/cpuset: Change callback_lock to raw_spinlock_t Waiman Long
2025-10-20 17:00   ` Tejun Heo [this message]
2025-10-20 19:25     ` Waiman Long

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