From nobody Sun Feb 8 13:39:31 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 60FDFEB64D9 for ; Mon, 10 Jul 2023 08:38:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232320AbjGJIiU (ORCPT ); Mon, 10 Jul 2023 04:38:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51350 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231215AbjGJIhy (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 B34BAE7; 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=BkEV7e94CvD29tG1A+d36LoGy9+Z10KJyC4UL+8m9vA=; b=E8fcE1zE/0LL0PTIC0UeKJ7pC2LWoMgmNJHt4pVpiUU9Iy50ohNZi5IlEz0wYRdZhyeDSK 69cL8rCVvP1lOnEGG0s3uAwtYW3qHaLgE3XZX9OlM2bD6Greuvq6Heng67GEUjckGhkMbi lCksUVzpyfHoSjaM8UuXQ4ysGwJ0RzRL/VFKt/B0TgFXmS+PORx+56EpSucKihp4t9MxHQ 7yEgDLy5gX2XWE1jEn8Sm0lP0R83CbvOqvQnG3eABsscgs/47i1lAOBy8Kl8FSEtc7GmzI IK4M0LeCDd4UVFBu67p0A2TKALfi58lOs1+H1Qmdmq2OuU2O5wS+Ur1MN+cEXg== 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=BkEV7e94CvD29tG1A+d36LoGy9+Z10KJyC4UL+8m9vA=; b=7WXTwqYYgsdP5/PLGDq/L4BOl1mLw/sgBUusU7m8IIQrc7V8NgSXa0mMTIKf64O0cIhfjx GHG7phTOQ5APlECg== 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/x86: Use local64_try_cmpxchg Cc: Uros Bizjak , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230706141720.2672-1-ubizjak@gmail.com> References: <20230706141720.2672-1-ubizjak@gmail.com> MIME-Version: 1.0 Message-ID: <168897827185.404.3533982389263997885.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: 4c1c9dea2089374cb58505a0df6136969ff3c8b9 Gitweb: https://git.kernel.org/tip/4c1c9dea2089374cb58505a0df6136969= ff3c8b9 Author: Uros Bizjak AuthorDate: Thu, 06 Jul 2023 16:16:48 +02:00 Committer: Peter Zijlstra CommitterDate: Mon, 10 Jul 2023 09:52:35 +02:00 perf/x86: Use local64_try_cmpxchg Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) =3D=3D = old. 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. "H. Peter Anvin" Signed-off-by: Uros Bizjak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230706141720.2672-1-ubizjak@gmail.com --- arch/x86/events/amd/ibs.c | 4 ++-- arch/x86/events/core.c | 10 ++++------ arch/x86/events/intel/cstate.c | 10 ++++------ arch/x86/events/msr.c | 8 +++----- 4 files changed, 13 insertions(+), 19 deletions(-) diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c index 74e6642..7d29be0 100644 --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -156,8 +156,8 @@ perf_event_try_update(struct perf_event *event, u64 new= _raw_count, int width) * count to the generic event atomically: */ prev_raw_count =3D local64_read(&hwc->prev_count); - if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) !=3D prev_raw_count) + if (!local64_try_cmpxchg(&hwc->prev_count, + &prev_raw_count, new_raw_count)) return 0; =20 /* diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 9d24870..23c9642 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -129,13 +129,11 @@ u64 x86_perf_event_update(struct perf_event *event) * exchange a new raw count - then add that new-prev delta * count to the generic event atomically: */ -again: prev_raw_count =3D local64_read(&hwc->prev_count); - rdpmcl(hwc->event_base_rdpmc, new_raw_count); - - if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) !=3D prev_raw_count) - goto again; + do { + rdpmcl(hwc->event_base_rdpmc, new_raw_count); + } while (!local64_try_cmpxchg(&hwc->prev_count, + &prev_raw_count, new_raw_count)); =20 /* * Now we have the new raw value and have updated the prev diff --git a/arch/x86/events/intel/cstate.c b/arch/x86/events/intel/cstate.c index 835862c..97035db 100644 --- a/arch/x86/events/intel/cstate.c +++ b/arch/x86/events/intel/cstate.c @@ -365,13 +365,11 @@ static void cstate_pmu_event_update(struct perf_event= *event) struct hw_perf_event *hwc =3D &event->hw; u64 prev_raw_count, new_raw_count; =20 -again: prev_raw_count =3D local64_read(&hwc->prev_count); - new_raw_count =3D cstate_pmu_read_counter(event); - - if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) !=3D prev_raw_count) - goto again; + do { + new_raw_count =3D cstate_pmu_read_counter(event); + } while (!local64_try_cmpxchg(&hwc->prev_count, + &prev_raw_count, new_raw_count)); =20 local64_add(new_raw_count - prev_raw_count, &event->count); } diff --git a/arch/x86/events/msr.c b/arch/x86/events/msr.c index 0feaaa5..61c59e0 100644 --- a/arch/x86/events/msr.c +++ b/arch/x86/events/msr.c @@ -244,12 +244,10 @@ static void msr_event_update(struct perf_event *event) s64 delta; =20 /* Careful, an NMI might modify the previous event value: */ -again: prev =3D local64_read(&event->hw.prev_count); - now =3D msr_read_counter(event); - - if (local64_cmpxchg(&event->hw.prev_count, prev, now) !=3D prev) - goto again; + do { + now =3D msr_read_counter(event); + } while (!local64_try_cmpxchg(&event->hw.prev_count, &prev, now)); =20 delta =3D now - prev; if (unlikely(event->hw.event_base =3D=3D MSR_SMI_COUNT)) {