From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794714225; b=1q4lHh/k1rwTKar3V17HQcwhdNW0edon5vunLxrTfyxugNVYEGqSq3fLhUJcvPyof+m3 hPeBkj1OcJdAZRkmaQcjZzNp8h6G9t7fSKM18cfpproLkPGOO1zbVQvBuN5iNqNarF86L LFl9HAhgMOEz9mqmvsDRbYfKh1RdKkw9JZ7DEe32bKfk5B+3ZiAGX4P5ofoztwfOlFhce 47uTi8wrCrxGspdq96k0EMKUkbFQljkVxU4ehsLkwWmFUFdxGN8xoj5bTtXV95Gxw7WnB RhdnwTA7MU2CHVXu9ZvL2HSyb/doI1K1wle1+MGJTCwO9v3309pFvoBrn2Wwu85As8A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794714225; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=fuu4w8y4QBhDhcl+D0bGJubWdG7NjDIVPTDRgmaLY50=; b=mRnv+ysDNVb1eXfxacdro6+3KUDppi84it8AlNex/KXUFzWxf2NWTH5XiFTIOhRrNeQn mcDBUM4yUtqXmqj1RrikBHhTsrBWwyw+m0KthusxsZ3SdJrIyN2KI2c61gUVRYiEe+T57 RExv9PD2jIFxNlmmEuvjcMV5HoFkIvj952xM4mTixA9JaxfpjUsslYTdFJh1Yj1sf++Zs E+WV0H+a/V+Dt/JPhrbXIjGfw8RYfMaVXa58ltzQz9l7xg+FzSySQNCpkScmeXXOp2pKo vA/G68clr/LEWSnOJzMniD6t4kGkiYkerssuf78jRZjDkvsqDLXKJIeCFDdyES1Yykw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=UBBgxW2Q; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with UTF8SMTPS id 16C7D606A327; Sun, 15 Nov 2026 03:43:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=UBBgxW2Q Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 2892D1F000C4; Sun, 15 Nov 2026 03:43:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794714224; bh=fuu4w8y4QBhDhcl+D0bGJubWdG7NjDIVPTDRgmaLY50=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=UBBgxW2QQ+H04TvxaOsthH8nhi77uGHQLQsuSeLr5a5JoSGXwXR2jcztp4jAtOevh YXUlIB+oQOa8ohY1FxX+k67D10dCIXBZhF4AK9ZjQeUH6Q0yxqlnl71aFlZyMjgIJ/ C4iVZJT2iJ/xGolYjMF2i2TPHNlo6cV888gy5MM0Og0VAXChREcvJyVZWghDN2NhxQ Ry+DaiLx2pOvwxFpDkBQFO3uZJwP8qQkVwOpt1IVdceU7CzBIeGvKRh3AZ/HYca/VS g8GIWFuZdrX5fr1hCrLaYj2jd2rMGjDX8JvRK5W1OZZ5ke8vJeFUivMxoNPOlA3HHs +BQTOv5i3ePhQ== Date: Sat, 14 Nov 2026 22:43:43 -0500 From: Joel Fernandes To: Chris Wiseman Cc: Frederic Weisbecker , "Paul E. McKenney" , Joel Fernandes , Joel Fernandes , Neeraj Upadhyay , Uladzislau Rezki , Boqun Feng , Josh Triplett , Tze-nan Wu , Cheng-jui Wang , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , 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 Message-ID: <20261115034343.GA1016414@joelbox> References: <18e815d3ba49a353.3137322e32332e3235332e313736.192c60.0000sendgmr@google.com> <20261115023115.GA3752240@joelbox> <18e81aaf93650e1b.3137322e32332e3235332e313736.231b55.0000sendgmr@google.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 > Thanks, > Chris