From nobody Mon Sep 15 01:54:08 2025 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 DA040C678D8 for ; Mon, 16 Jan 2023 17:14:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234393AbjAPROh (ORCPT ); Mon, 16 Jan 2023 12:14:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234406AbjAPRNL (ORCPT ); Mon, 16 Jan 2023 12:13:11 -0500 Received: from mail-ej1-x62a.google.com (mail-ej1-x62a.google.com [IPv6:2a00:1450:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A1FAB4B759 for ; Mon, 16 Jan 2023 08:53:47 -0800 (PST) Received: by mail-ej1-x62a.google.com with SMTP id ss4so62192799ejb.11 for ; Mon, 16 Jan 2023 08:53:47 -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=F3gL+vo2nZmaFGXvjiyowbCSgFOPmttF0YcJ6ksoAuA=; b=b3vWesy3yIjbd7kfnRDBv7O4TQTs9bjG225BOHTPHukn2haXOrIs6YdnRG6umF7oVd SB/gLzXe9Y43xtiRGEwapaadKT/yLns5dnogdox+NEkw81qclMZGr0zOdaHdqm0zACU/ nFAc+RgHUWwatXJSDIiPHgMuDGZbuckw8XMHBHaO3422Oo3JQa+5U3Mpihk9Ftf5ZBIa 9YjUsozQryMT8f2gO+HWSHcXRr6wBEUIiO1PMxMZyrxupubK7uCh5yNWiFPN/E5z6Sz8 tx/xcwMDG2IN38L14OYKcNhkwwfS0AwCkGtXU7rT7mkB8zVWuNZ7uxlNvQO7g057ARJV tqsw== 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=F3gL+vo2nZmaFGXvjiyowbCSgFOPmttF0YcJ6ksoAuA=; b=e0WILYlFZBTuOhWQlQmnXD0qH8LkDqW3Y/e3ZaJe4USKC2xJON+OzhTw0vU7HcDozs dwll9q5FOHMOL6ZsI3xl+5kTpUpuX10Npsdi7X/kL0QrzMQq11ze7lANxmorlWM7AcMF gNebXO8ebzqTtsu5ZmMPTXC/Ou6GsUL6SGzOv3zoETuLYipT9UfCwMzwb0q+a64shggN H4LyT8uHQy29FIAYh61wnwvj3jITDTiu8dPxa1O0DTWXhw7aSa2uGFY5swp9ZpsiqQTR t4AasUDE5fEGdaHfaudHdnF2O3TQdiIbk3riW6czeAthp2bHMduPHqRFPsQqpzw9npJi FeMA== X-Gm-Message-State: AFqh2kpHI6aRycRo9+tX7xPsfQzP5ffmNJdUOvwzJoK2HTYnIFFzcVQn eIEH1Tnkl0Z3wEt0VLT4Irl3rEAjf8icIw== X-Google-Smtp-Source: AMrXdXum1Bwh3I00Nbb/8scZeAlFOnU5KqM+bC5zHR1QHXP+mgXWBkqimqNz+jBx/jZU7ePYDjDlPQ== X-Received: by 2002:a17:906:7c3:b0:85a:4230:756c with SMTP id m3-20020a17090607c300b0085a4230756cmr26101249ejc.59.1673888025936; Mon, 16 Jan 2023 08:53:45 -0800 (PST) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id 1-20020a170906308100b007a8de84ce36sm11956785ejv.206.2023.01.16.08.53.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Jan 2023 08:53:45 -0800 (PST) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Thomas Gleixner Subject: [PATCH] posix-timers: use atomic64_try_cmpxchg in __update_gt_cputime Date: Mon, 16 Jan 2023 17:53:37 +0100 Message-Id: <20230116165337.5810-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Use atomic64_try_cmpxchg instead of atomic64_cmpxchg (*ptr, old, new) =3D= =3D old in __update_gt_cputime. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic64_try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. No functional change intended. Signed-off-by: Uros Bizjak Cc: Thomas Gleixner --- kernel/time/posix-cpu-timers.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index cb925e8ef9a8..2f5e9b34022c 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -243,13 +243,12 @@ static void proc_sample_cputime_atomic(struct task_cp= utime_atomic *at, */ static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputim= e) { - u64 curr_cputime; -retry: - curr_cputime =3D atomic64_read(cputime); - if (sum_cputime > curr_cputime) { - if (atomic64_cmpxchg(cputime, curr_cputime, sum_cputime) !=3D curr_cputi= me) - goto retry; - } + u64 curr_cputime =3D atomic64_read(cputime); + + do { + if (sum_cputime <=3D curr_cputime) + return; + } while (!atomic64_try_cmpxchg(cputime, &curr_cputime, sum_cputime)); } =20 static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic, --=20 2.39.0