From: Breno Leitao <leitao@debian.org>
To: Waiman Long <longman@redhat.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Uladzislau Rezki <urezki@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
Vratislav Bendel <vbendel@redhat.com>
Subject: Re: [PATCH] rcu: Use system_unbound_wq to avoid disturbing isolated CPUs
Date: Wed, 24 Jul 2024 06:30:29 -0700 [thread overview]
Message-ID: <ZqEB9Yz0womtmDRg@gmail.com> (raw)
In-Reply-To: <20240723181025.187413-1-longman@redhat.com>
On Tue, Jul 23, 2024 at 02:10:25PM -0400, Waiman Long wrote:
> It was discovered that isolated CPUs could sometimes be disturbed by
> kworkers processing kfree_rcu() works causing higher than expected
> latency. It is because the RCU core uses "system_wq" which doesn't have
> the WQ_UNBOUND flag to handle all its work items. Fix this violation of
> latency limits by using "system_unbound_wq" in the RCU core instead.
> This will ensure that those work items will not be run on CPUs marked
> as isolated.
>
> Beside the WQ_UNBOUND flag, the other major difference between system_wq
> and system_unbound_wq is their max_active count. The system_unbound_wq
> has a max_active of WQ_MAX_ACTIVE (512) while system_wq's max_active
> is WQ_DFL_ACTIVE (256) which is half of WQ_MAX_ACTIVE.
>
> Reported-by: Vratislav Bendel <vbendel@redhat.com>
I've seen this problem a while ago and reported to the list:
https://lore.kernel.org/all/Zp906X7VJGNKl5fW@gmail.com/
I've just applied this test, and run my workload for 2 hours without
hitting this issue. Thanks for solving it.
Tested-by: Breno Leitao <leitao@debian.org>
next prev parent reply other threads:[~2024-07-24 13:30 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-07-23 18:10 [PATCH] rcu: Use system_unbound_wq to avoid disturbing isolated CPUs Waiman Long
2024-07-24 10:30 ` Uladzislau Rezki
2024-07-24 13:30 ` Breno Leitao [this message]
2024-07-24 14:23 ` Uladzislau Rezki
2024-07-29 3:06 ` Waiman Long
2024-07-25 15:35 ` Neeraj Upadhyay
2024-07-25 17:02 ` Waiman Long
2024-07-25 19:33 ` Neeraj Upadhyay
2024-07-25 19:52 ` Waiman Long
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