From patchwork Tue Feb 28 15:51:21 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Uros Bizjak X-Patchwork-Id: 13155048 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 5480FC64EC7 for ; Tue, 28 Feb 2023 15:51:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230056AbjB1Pve (ORCPT ); Tue, 28 Feb 2023 10:51:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229881AbjB1Pvd (ORCPT ); Tue, 28 Feb 2023 10:51:33 -0500 Received: from mail-ed1-x535.google.com (mail-ed1-x535.google.com [IPv6:2a00:1450:4864:20::535]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 88D4231E35; Tue, 28 Feb 2023 07:51:32 -0800 (PST) Received: by mail-ed1-x535.google.com with SMTP id i34so41882549eda.7; Tue, 28 Feb 2023 07:51:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=wUCY23lI6ZJvR/D1w3pZEq+r1szcr1TztpwRWIRWSoQ=; b=Z6mCyrlrP7F8GnsWHKAzm2VDvru9DuR70y50S672b+2tf42utVlWYAMTcdZLt9WXud /375YOW3sy1WhIXDwbFu/oamI5ub0Gwxn0RPFig7qzRm+eu5gFAqInUCc+ZqmxqBS2Dy IBZNVoeXtoZpqSlPuyEYGgx5O9RfwpCFyxMpmx4pYho6KGj9Y4CROqCaYkQKDXfJENq1 XeCD+kXP/3izj9acGl61Kai8elcAPWB49yjAVn6D6pPPKYoUAIbEAdXytWOdND4loVdR zpzHQsNgeVWYpXmLloU8xk4laIlZBO/2KpYPBek9axg7BozJVOgTu/FSFu1IjQPhTOl4 jDSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=wUCY23lI6ZJvR/D1w3pZEq+r1szcr1TztpwRWIRWSoQ=; b=rhgmY6yPB3/DqSE+x6Oxi9QllaNwVCthz7iJj57bZiT1er54RWQA3s3zWyirfVJBm4 jaecL41r8cRyO6ymayF69B4bnbL9B7R7hE220HD8erV2lXTTA/BwztjzJBiXGdwpCXrK FlSOOJbX6kTay0qCEpvWZm7pa1Ti6vOUSUQH6huuTX8iGpGPgVWLkM3tMRt0OJrLggNI Gtm5/HAe6tXwMKZRmNPMYePdultbQQr+vv4JFc5Az0Sf8pammU1l2czsL5NMDitZxqzO rOjQhq5SNVScDFIQvX8dchIFYJAkGdwdR3mRKpB5jPaTcjU/PTbTN6FIBShdc41rAIIg 1doQ== X-Gm-Message-State: AO0yUKXwn8UlHdZNTOqfZvKUA4CubwjuY/7fmwk6jSauKqBOEy6ozSwX x5fSMe8mKPtnttVl4YejtoyDLsJ/BhU1PCYQ X-Google-Smtp-Source: AK7set8VwCCjeSGdZlGi3/DAducTmZMUHb7uOpZwdANzLOxS/Smu4zf8eI0y3Pvle/mxOWaljDsyqw== X-Received: by 2002:a05:6402:1a39:b0:4aa:b310:b695 with SMTP id be25-20020a0564021a3900b004aab310b695mr3573472edb.35.1677599490660; Tue, 28 Feb 2023 07:51:30 -0800 (PST) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id x16-20020a170906441000b008d09b900614sm4577153ejo.80.2023.02.28.07.51.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Feb 2023 07:51:30 -0800 (PST) From: Uros Bizjak To: rcu@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes Subject: [PATCH] rcu: use try_cmpxchg in check_cpu_stall Date: Tue, 28 Feb 2023 16:51:21 +0100 Message-Id: <20230228155121.3416-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in check_cpu_stall. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). No functional change intended. Cc: "Paul E. McKenney" Cc: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Signed-off-by: Uros Bizjak Acked-by: Joel Fernandes (Google) --- kernel/rcu/tree_stall.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index b10b8349bb2a..d81c88e66b42 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -760,7 +760,7 @@ static void check_cpu_stall(struct rcu_data *rdp) jn = jiffies + ULONG_MAX / 2; if (rcu_gp_in_progress() && (READ_ONCE(rnp->qsmask) & rdp->grpmask) && - cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { + try_cmpxchg(&rcu_state.jiffies_stall, &js, jn)) { /* * If a virtual machine is stopped by the host it can look to @@ -778,7 +778,7 @@ static void check_cpu_stall(struct rcu_data *rdp) } else if (rcu_gp_in_progress() && ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) && - cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { + try_cmpxchg(&rcu_state.jiffies_stall, &js, jn)) { /* * If a virtual machine is stopped by the host it can look to