From patchwork Wed Nov 30 18:13:20 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 630807 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D10F1C46467 for ; Wed, 30 Nov 2022 18:14:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230226AbiK3SOL (ORCPT ); Wed, 30 Nov 2022 13:14:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39154 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230003AbiK3SNd (ORCPT ); Wed, 30 Nov 2022 13:13:33 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6D8772B609; Wed, 30 Nov 2022 10:13:32 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id B3B28CE1ACE; Wed, 30 Nov 2022 18:13:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DB98C4314F; Wed, 30 Nov 2022 18:13:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1669832008; bh=JWSyRakhy+dkVAOMqz8EUh288eeQKUxl8b8ecP4VVOs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g/yaPLuZPzWktPAHagD6UFkCYaDu8tya1qQO49HjS1nedSCUGvwEWFpmtPHku1wc2 WKZPghDQCNGvnOhydYxN1R0NSOOckw+eT5aU1qcoSTT05VhnZRw3wu/E90O08NPgpU NX9XrGUbGKD4FzAFyCc7HuXqlG/Mi0SITZt9VByrOA+0i6cqH8+yLOjto2RyAOgS1s eGSk6cgv9sxqd5ksp9JSLSqbauqpUvfyqNwsOqo0Xf1gJ+kOiWGIZZacgEZB1NekX6 stuVJWxwItCP9uutcpBfLHSIkmR6iBv9E4bASwgu7M8bj+7KpkUbx6s60il2mpyLxZ S1HtBhZ/Neqpw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 69A615C1722; Wed, 30 Nov 2022 10:13:27 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, Uladzislau Rezki , Joel Fernandes , "James E.J. Bottomley" , linux-scsi@vger.kernel.org, Bart Van Assche , "Martin K . Petersen" , "Paul E . McKenney" Subject: [PATCH rcu 11/16] scsi/scsi_error: Use call_rcu_hurry() instead of call_rcu() Date: Wed, 30 Nov 2022 10:13:20 -0800 Message-Id: <20221130181325.1012760-11-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221130181316.GA1012431@paulmck-ThinkPad-P17-Gen-1> References: <20221130181316.GA1012431@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org From: Uladzislau Rezki Earlier commits in this series allow battery-powered systems to build their kernels with the default-disabled CONFIG_RCU_LAZY=y Kconfig option. This Kconfig option causes call_rcu() to delay its callbacks in order to batch them. This means that a given RCU grace period covers more callbacks, thus reducing the number of grace periods, in turn reducing the amount of energy consumed, which increases battery lifetime which can be a very good thing. This is not a subtle effect: In some important use cases, the battery lifetime is increased by more than 10%. This CONFIG_RCU_LAZY=y option is available only for CPUs that offload callbacks, for example, CPUs mentioned in the rcu_nocbs kernel boot parameter passed to kernels built with CONFIG_RCU_NOCB_CPU=y. Delaying callbacks is normally not a problem because most callbacks do nothing but free memory. If the system is short on memory, a shrinker will kick all currently queued lazy callbacks out of their laziness, thus freeing their memory in short order. Similarly, the rcu_barrier() function, which blocks until all currently queued callbacks are invoked, will also kick lazy callbacks, thus enabling rcu_barrier() to complete in a timely manner. However, there are some cases where laziness is not a good option. For example, synchronize_rcu() invokes call_rcu(), and blocks until the newly queued callback is invoked. It would not be a good for synchronize_rcu() to block for ten seconds, even on an idle system. Therefore, synchronize_rcu() invokes call_rcu_hurry() instead of call_rcu(). The arrival of a non-lazy call_rcu_hurry() callback on a given CPU kicks any lazy callbacks that might be already queued on that CPU. After all, if there is going to be a grace period, all callbacks might as well get full benefit from it. Yes, this could be done the other way around by creating a call_rcu_lazy(), but earlier experience with this approach and feedback at the 2022 Linux Plumbers Conference shifted the approach to call_rcu() being lazy with call_rcu_hurry() for the few places where laziness is inappropriate. And another call_rcu() instance that cannot be lazy is the one in the scsi_eh_scmd_add() function. Leaving this instance lazy results in unacceptably slow boot times. Therefore, make scsi_eh_scmd_add() use call_rcu_hurry() in order to revert to the old behavior. [ paulmck: Apply s/call_rcu_flush/call_rcu_hurry/ feedback from Tejun Heo. ] Tested-by: Joel Fernandes (Google) Signed-off-by: Uladzislau Rezki Signed-off-by: Joel Fernandes (Google) Cc: "James E.J. Bottomley" Cc: Reviewed-by: Bart Van Assche Acked-by: Martin K. Petersen Signed-off-by: Paul E. McKenney --- drivers/scsi/scsi_error.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c index 6995c89792300..ac5ff0783b4f0 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -312,7 +312,7 @@ void scsi_eh_scmd_add(struct scsi_cmnd *scmd) * Ensure that all tasks observe the host state change before the * host_failed change. */ - call_rcu(&scmd->rcu, scsi_eh_inc_host_failed); + call_rcu_hurry(&scmd->rcu, scsi_eh_inc_host_failed); } /**