From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 212073BBEB; Wed, 9 Oct 2024 14:37:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728484638; cv=none; b=YsL1Ux+dS9RVEeM7/KJcpThXf0djfyUVsLvaXxqkOcETmgLbb0bzAVs9OPyqt3zGhN8Hk9IP4xe7Y2Wj2huEBWeD2w/SfJ+Dl+hPHDKAlwigYOIcSzX2qLeqSh7TjYy038Ij98JEce9h9AVi56o2jA29XHgbxSSjp/w+VQPC0d0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728484638; c=relaxed/simple; bh=6fyn3wX+UwlDxoFQS10FOggWv6S8FSIec9HdLXYbHxU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JuxVlqAHi9CipjUxt5g1I/BmCl6g2GnAnqgUvReG1HLZ2/dThfyNKnvvGjDAPh2flTdvZuW+ZBwwfWIJnpr+hgv3XUcBIJSSwAJafnR5IrsJSOmjA0AMez+vnaviCp++/eU1hYAXlus/4uUOnQDFECfpbsKtRnd79xkoZIU2ZiM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q+S4h6Vo; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Q+S4h6Vo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DC1DC4CEC3; Wed, 9 Oct 2024 14:37:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728484637; bh=6fyn3wX+UwlDxoFQS10FOggWv6S8FSIec9HdLXYbHxU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Q+S4h6VoePLaSWMBaEZrbTs5ASdKkvAOjlKthj0fp8joS4AmF1JcBHYOMPZxYw6Sz V32pMsyP+OiL4TR74WdnAd+qUtDHYr7x3LDOPbaF35FzS/GNz3r2POVKD6yJtyAmqD L2AsDc9Phr0IU/yz9J1BrhxDxaIh8xeFy4kfukTzhyhpFsm/N4yKnlnXwxrFMF8YXc zjPH1Y7/Bck8QrzjXZ+LMViawL39SsmnUFmnetI5zNG/mR6M3IzVr55b61X66V03LB J/ysOtMPvwHT7mOLPaAOdBrvNLtH0fP8Fl9LWQd8trT4/qDN9ujZ9Agio0s6pF2sJj u8nCmY2NhHbaw== Date: Wed, 9 Oct 2024 16:37:14 +0200 From: Frederic Weisbecker To: neeraj.upadhyay@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, paulmck@kernel.org, joel@joelfernandes.org, boqun.feng@gmail.com, urezki@gmail.com, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang1211@gmail.com, peterz@infradead.org, neeraj.upadhyay@amd.com Subject: Re: [PATCH v2 07/10] rcu/tasks: Check RCU watching state for holdout idle injection tasks Message-ID: References: <20241009125127.18902-1-neeraj.upadhyay@kernel.org> <20241009125127.18902-8-neeraj.upadhyay@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241009125127.18902-8-neeraj.upadhyay@kernel.org> Le Wed, Oct 09, 2024 at 06:21:24PM +0530, neeraj.upadhyay@kernel.org a écrit : > From: Neeraj Upadhyay > > Use RCU watching state of a CPU to check whether RCU-tasks GP > need to wait for idle injection task on that CPU. Idle injection > tasks which are in deep-idle states where RCU is not watching or > which have transitioned to/from deep-idle state do not block > RCU-tasks grace period. > > Signed-off-by: Neeraj Upadhyay For now this should work because there is a single user that is a per-cpu kthread, therefore no RCU-watching writer can race against another (real idle VS idle injection or idle_injection VS idle injection) without going first through a voluntary context switch. But who knows about the future? If an idle injection kthread is preempted by another idle injection right after clearing PF_IDLE, there could be some spurious QS accounted for the preempted kthread. So perhaps we can consider idle injection as any normal task and wait for it to voluntary schedule? Well I see DEFAULT_DURATION_JIFFIES = 6, which is 60 ms on HZ=100. Yeah that's a lot...so perhaps this patch is needed after all... > --- > kernel/rcu/tasks.h | 63 +++++++++++++++++++++++++++++++++++----------- > 1 file changed, 48 insertions(+), 15 deletions(-) > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > index d8506d2e6f54..1947f9b6346d 100644 > --- a/kernel/rcu/tasks.h > +++ b/kernel/rcu/tasks.h > @@ -38,6 +38,8 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp); > * @rtpp: Pointer to the rcu_tasks structure. > * @rcu_watching_snap: Per-GP RCU-watching snapshot for idle tasks. > * @rcu_watching_snap_rec: RCU-watching snapshot recorded for idle task. > + * @rcu_watching_idle_inj_snap: Per-GP RCU-watching snapshot for idle inject task. > + * @rcu_watching_idle_inj_rec: RCU-watching snapshot recorded for idle inject task. > */ > struct rcu_tasks_percpu { > struct rcu_segcblist cblist; > @@ -56,6 +58,8 @@ struct rcu_tasks_percpu { > struct rcu_tasks *rtpp; > int rcu_watching_snap; > bool rcu_watching_snap_rec; > + int rcu_watching_idle_inj_snap; > + bool rcu_watching_idle_inj_rec; So how about: struct rcu_watching_task { int snap; bool rec; } ... struct rcu_tasks_percpu { ... struct rcu_watching_task idle_task; struct rcu_watching_task idle_inject; } Thanks.