From nobody Sun Feb 8 09:27:46 2026 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 AA00CEB64D9 for ; Mon, 10 Jul 2023 08:38:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230492AbjGJIiC (ORCPT ); Mon, 10 Jul 2023 04:38:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51338 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230477AbjGJIhy (ORCPT ); Mon, 10 Jul 2023 04:37:54 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 501D7E6; Mon, 10 Jul 2023 01:37:53 -0700 (PDT) Date: Mon, 10 Jul 2023 08:37:51 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1688978272; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SUn+6Bo1QBKBDK8RwHrPsSPwL7VkjRzPfS9/sg4u31c=; b=M06fGKAE6ERw5kLlpZVH/oGeAXIfutzXNjrVHaTNY0+LfYNz3SVhofFih2djuPpTu/wxym cpg7RIx5SAeWxfl++M/5N/oXje9d3PsrcLWug31KsCEdPCeEJK6Suy03XwLqe8kJEAKv1v 5htR/HyXst+a66Pt5yWtaQeSpqv+WnSD81eiWcfK9OVAXRoFhbeLRrqRDV+gnxIKzQRHZt gWw3YxqAg16scveBvdoVS/ns2bvhsSIdvWcIfhknyuw2i9nrdbI3I5dBCTYZuQqOmA8WC+ 6Zs/SHBofcvOp+QKUBIapJ4qe8FMZnRm6OO/UoN7Y14VLF6ZVsbF/841AEWUPw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1688978272; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SUn+6Bo1QBKBDK8RwHrPsSPwL7VkjRzPfS9/sg4u31c=; b=8vptgk6J3Ee6tJikx/zsVGwBt4ClhLlWY8hA+syearJDRE/Ss5P9TAj0U+HaZC66ORj5+Z janxNOAO5nRSflCg== From: "tip-bot2 for Uros Bizjak" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: perf/core] perf/core: Use local64_try_cmpxchg in perf_swevent_set_period Cc: Uros Bizjak , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230708081129.45915-1-ubizjak@gmail.com> References: <20230708081129.45915-1-ubizjak@gmail.com> MIME-Version: 1.0 Message-ID: <168897827147.404.3167586601225398989.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the perf/core branch of tip: Commit-ID: 28fd85a10a2a73658c6e26056d9e093de06b5a22 Gitweb: https://git.kernel.org/tip/28fd85a10a2a73658c6e26056d9e093de= 06b5a22 Author: Uros Bizjak AuthorDate: Sat, 08 Jul 2023 10:10:57 +02:00 Committer: Peter Zijlstra CommitterDate: Mon, 10 Jul 2023 09:52:35 +02:00 perf/core: Use local64_try_cmpxchg in perf_swevent_set_period Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) =3D=3D = 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. Signed-off-by: Uros Bizjak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230708081129.45915-1-ubizjak@gmail.com --- 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 78ae7b6..f84e264 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9595,16 +9595,16 @@ u64 perf_swevent_set_period(struct perf_event *even= t) =20 hwc->last_period =3D hwc->sample_period; =20 -again: - old =3D val =3D local64_read(&hwc->period_left); - if (val < 0) - return 0; + old =3D local64_read(&hwc->period_left); + do { + val =3D old; + if (val < 0) + return 0; =20 - nr =3D div64_u64(period + val, period); - offset =3D nr * period; - val -=3D offset; - if (local64_cmpxchg(&hwc->period_left, old, val) !=3D old) - goto again; + nr =3D div64_u64(period + val, period); + offset =3D nr * period; + val -=3D offset; + } while (!local64_try_cmpxchg(&hwc->period_left, &old, val)); =20 return nr; }