From nobody Tue Dec 16 11:06:48 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 6F1F2E776FD for ; Tue, 3 Oct 2023 19:19:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240904AbjJCTTM (ORCPT ); Tue, 3 Oct 2023 15:19:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230239AbjJCTTL (ORCPT ); Tue, 3 Oct 2023 15:19:11 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A0759E; Tue, 3 Oct 2023 12:19:08 -0700 (PDT) Date: Tue, 03 Oct 2023 19:19:05 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1696360746; 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=vXwvdKEZsex1mUoiT3XttWgQj+pJN6iq2V/O4MOUH1I=; b=FUxtqVW8OwpMOV8Ywim0HCwzrO6/sb/8hP3enKsQn9QkZhuTQzR+ci9of6smeIDYtvVmDr 9TOIGWRNlMlToaGAzZahrVSznPSWUUQk/yXJwOUbDmdpNHq55bRf/v6EpiAUYJBVMv5wbx sX44BhGWeHGTbzqV8wiDa3eslY+9KGVdAxvBFgGsHHEYBGkmuKvACId8HtLl0U3aKEj16w L3x0wfs7doDdlAKq861bKJ7nTcm3hxZ+ut4XMcL4rSR2D3WB3rm3W8d/DLo+Kzw2sB3JS1 7kYmRzdguc/OQk7BsG/N8yl5EZUdqUAC+Dulhn2wmTWhKod04HVYB5B9b+1GLw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1696360746; 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=vXwvdKEZsex1mUoiT3XttWgQj+pJN6iq2V/O4MOUH1I=; b=9fdDZ6GSljP3XkgxfSA43gwqQi42+Oaae0fwYXfLK2Tz78sS8/L/bbJja9dGmyWpG0FZhZ nTcQ3SCKfQa+iIBg== 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/rapl: Use local64_try_cmpxchg in rapl_event_update() Cc: Uros Bizjak , Ingo Molnar , Peter Zijlstra , Linus Torvalds , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230807145134.3176-2-ubizjak@gmail.com> References: <20230807145134.3176-2-ubizjak@gmail.com> MIME-Version: 1.0 Message-ID: <169636074590.3135.6268444567676526920.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: bcc6ec3d954bbcc8bec34a21c05ea536a2e96d6f Gitweb: https://git.kernel.org/tip/bcc6ec3d954bbcc8bec34a21c05ea536a= 2e96d6f Author: Uros Bizjak AuthorDate: Mon, 07 Aug 2023 16:51:15 +02:00 Committer: Ingo Molnar CommitterDate: Tue, 03 Oct 2023 21:13:45 +02:00 perf/x86/rapl: Use local64_try_cmpxchg in rapl_event_update() 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. Signed-off-by: Uros Bizjak Signed-off-by: Ingo Molnar Cc: Peter Zijlstra Cc: Linus Torvalds Cc: "H. Peter Anvin" Link: https://lore.kernel.org/r/20230807145134.3176-2-ubizjak@gmail.com --- arch/x86/events/rapl.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/arch/x86/events/rapl.c b/arch/x86/events/rapl.c index e8f53b2..6d3e738 100644 --- a/arch/x86/events/rapl.c +++ b/arch/x86/events/rapl.c @@ -179,13 +179,11 @@ static u64 rapl_event_update(struct perf_event *event) s64 delta, sdelta; int shift =3D RAPL_CNTR_WIDTH; =20 -again: prev_raw_count =3D local64_read(&hwc->prev_count); - rdmsrl(event->hw.event_base, new_raw_count); - - if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) !=3D prev_raw_count) - goto again; + do { + rdmsrl(event->hw.event_base, 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