From: Joel Fernandes <jfern@kernel.org>
To: Chris Wiseman <chriswiseman@google.com>
Cc: Frederic Weisbecker <frederic@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Joel Fernandes <joelagnelf@nvidia.com>,
Joel Fernandes <joel@joelfernandes.org>,
Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
Uladzislau Rezki <urezki@gmail.com>,
Boqun Feng <boqun@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Tze-nan Wu <Tze-nan.Wu@mediatek.com>,
Cheng-jui Wang <cheng-jui.wang@mediatek.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang@linux.dev>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] rcu/nocb: Keep lazy timer intact on second lazy callback
Date: Sat, 14 Nov 2026 22:43:43 -0500 [thread overview]
Message-ID: <20261115034343.GA1016414@joelbox> (raw)
In-Reply-To: <18e81aaf93650e1b.3137322e32332e3235332e313736.231b55.0000sendgmr@google.com>
On chriswiseman@google.com wrote:
> Hi Joel,
>
> > Looks reasonable to me. Is there a test case that you added to find this, or any
> > power savings that you found with this added patch?
>
> I spotted this while tracing idle rcuog wakeups with CONFIG_RCU_LAZY=y
> and rcu_nocbs=all, where rcuog kept waking up after 1 jiffy whenever a
> second CPU in the group queued a lazy callback. I verified it with
> rcutorture (NOCB01) and measured a light background callback workload on
> an arm64 system:
>
> Before After Delta
> rcuog wakeups: 1,885 1,174 -37.7%
> 1-jiffy timer resets: 739 0 -100.0%
> SoC power (CPU+DSU): 94.1 mW 76.5 mW -18.6% (-17.5 mW)
>
Looks nice! I will apply the patch and run some tests.
Reviewed-by: Joel Fernandes <jfern@kernel.org>
> Thanks,
> Chris
prev parent reply other threads:[~2026-11-15 3:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-15 2:07 [PATCH] rcu/nocb: Keep lazy timer intact on second lazy callback Chris Wiseman
2026-11-15 2:31 ` jfern
2026-11-15 3:36 ` Chris Wiseman
2026-11-15 3:43 ` Joel Fernandes [this message]
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