From mboxrd@z Thu Jan 1 00:00:00 1970 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 670E6EB64DA for ; Sat, 8 Jul 2023 08:11:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229515AbjGHILm (ORCPT ); Sat, 8 Jul 2023 04:11:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35690 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229458AbjGHILl (ORCPT ); Sat, 8 Jul 2023 04:11:41 -0400 Received: from mail-ej1-x629.google.com (mail-ej1-x629.google.com [IPv6:2a00:1450:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AA0A41FC6; Sat, 8 Jul 2023 01:11:40 -0700 (PDT) Received: by mail-ej1-x629.google.com with SMTP id a640c23a62f3a-992e22c09edso291002666b.2; Sat, 08 Jul 2023 01:11:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1688803899; x=1691395899; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=8JsdPx2PtCEj+8E+tenBNbAlijTmNN2EqyVkNdLKfmA=; b=rztSuS3v+nITm9k3tsJpLSvmzVE3zy9CxeLeSXc2C6hpHHlu2JWiOTJmiANEYXz9pa iPNmy94s66MAl+pmwGTHc1dkeRYJxxQDbXmcWl6fhLsOIuSdIlWd5Bfw6O2nJGkl0U+/ CYuYrEq4hj9/MHupnUWYHz7Ygb+LIigJ1xJmhiWGLaBlhPq2lURUNwgb413C3KSfORZw 1FBMHI9eN/zKizPlb5EFvAReSLChWeiyq3/pOvs94erbRLbyUlygcSf19EZItjuW0nOI KJ0/ocl1jx9c1QMuqqhkaPT80vfWEANYQOUVPEv4EuTgVONyi0KDN7TCGXv5e/po78KZ F7SA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688803899; x=1691395899; 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=8JsdPx2PtCEj+8E+tenBNbAlijTmNN2EqyVkNdLKfmA=; b=bUcnoeMY4piGJZY48ju6Wvt+NPrJVu+gIqRzQAXXWcIilUkxSX12ojVGH7oCqbFWLk O9nME9jlHPx+rzVDWW/9875PUulfQE6w2LsT+JgXqJQyc2Xk7sspx8+21rVHHidAfcV4 ajmyajA+f/4bhQwbsivBBMY1vs+LeV0DJRpWL08E5afMkKdDGL5I3L3q2CflbmCopIuf xBgUC1UW5j5uBSSk1kqHRPJ/AIly93pp0EULnWaaSEb9/jmxFlwIlnziLeQ/A0bMS44X 9qF/mQzh6+8Fub70wJFQcCbvVODIty2rNAJRQu/FZguA7lRaW/FNchzHZFCwXQfocOey ny7w== X-Gm-Message-State: ABy/qLbvquXMrTXvhtW2PcJsxAvn6o1or2Ckaq0emN5C5k/Rnq2Kb+1H sU8s/Cs4ShPu9VJT2HsSqtVLsoKXZ2Qhrw== X-Google-Smtp-Source: APBJJlE4SRjJJSfqI47lKi2L1n2FIAQTgGAQPjLr+o2ro9brA/66+l23EdfRFaJ7W2iUuGXDneiVYA== X-Received: by 2002:a17:906:79c4:b0:982:9daf:9fcf with SMTP id m4-20020a17090679c400b009829daf9fcfmr5197948ejo.66.1688803898582; Sat, 08 Jul 2023 01:11:38 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id cw23-20020a170906c79700b0098963eb0c3dsm3152939ejb.26.2023.07.08.01.11.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Jul 2023 01:11:38 -0700 (PDT) From: Uros Bizjak To: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter Subject: [PATCH] perf/core: Use local64_try_cmpxchg in perf_swevent_set_period Date: Sat, 8 Jul 2023 10:10:57 +0200 Message-ID: <20230708081129.45915-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old in perf_swevent_set_period. 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, 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. Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Cc: Mark Rutland Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Namhyung Kim Cc: Ian Rogers Cc: Adrian Hunter Signed-off-by: Uros Bizjak --- kernel/events/core.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 78ae7b6f90fd..f84e2640ea2f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9595,16 +9595,16 @@ u64 perf_swevent_set_period(struct perf_event *event) hwc->last_period = hwc->sample_period; -again: - old = val = local64_read(&hwc->period_left); - if (val < 0) - return 0; + old = local64_read(&hwc->period_left); + do { + val = old; + if (val < 0) + return 0; - nr = div64_u64(period + val, period); - offset = nr * period; - val -= offset; - if (local64_cmpxchg(&hwc->period_left, old, val) != old) - goto again; + nr = div64_u64(period + val, period); + offset = nr * period; + val -= offset; + } while (!local64_try_cmpxchg(&hwc->period_left, &old, val)); return nr; } -- 2.41.0