From nobody Sun Feb 8 10:33:19 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 E85CEEB64DA for ; Mon, 10 Jul 2023 08:38:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231624AbjGJIiN (ORCPT ); Mon, 10 Jul 2023 04:38:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230298AbjGJIhx (ORCPT ); Mon, 10 Jul 2023 04:37:53 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DC6DC3; Mon, 10 Jul 2023 01:37:52 -0700 (PDT) Date: Mon, 10 Jul 2023 08:37:50 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1688978271; 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=ilamyJDbICYtSDb02PIB2zgJt9yweTD8M1ng84MwQtQ=; b=yvC0+IPHasmDZAPNA/tb0hmOSfp/3yyOH4FFI8TPzUkrkomA6ew0odlx8y9qf6aZzPnjUR xdRHtaE/YuldyorlD5vcipUXK/FcsdKy4YNW/mqJpSeVvg3ibcXvU/V9dEorv5t3B0CRU4 BIUokeaIxmBcEHjgKepNpYYmSxAPONrqrNwTfhKqA9YAE2g8MaqlPUvacqL5IlDkXetfdd qBuYTmh/B4cBJQx4CX0tTJ7hKrnyy78f9xdvSwNifipK0CONopMDBdkBqKZAnuM9Dz9mkM XlNdhvvpvELX5OnigvsU3l3NB96ERbFwduEDQSoSTkbtbuWzLPOOjhHOfFqiWw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1688978271; 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=ilamyJDbICYtSDb02PIB2zgJt9yweTD8M1ng84MwQtQ=; b=AtiqU7oQOKOd+xFWe3ucgcLxmVux0idjwNTHPEyjZhlikqzfphk/giRBlHB0g0zH0zqrFf 847qAlusQXOm4hDg== 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/ring_buffer: Use local_try_cmpxchg in __perf_output_begin Cc: Uros Bizjak , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230708090048.63046-2-ubizjak@gmail.com> References: <20230708090048.63046-2-ubizjak@gmail.com> MIME-Version: 1.0 Message-ID: <168897827031.404.10627731369793852895.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: 1af61adb3a23192023fec1733bd4c8500f53e546 Gitweb: https://git.kernel.org/tip/1af61adb3a23192023fec1733bd4c8500= f53e546 Author: Uros Bizjak AuthorDate: Sat, 08 Jul 2023 11:00:37 +02:00 Committer: Peter Zijlstra CommitterDate: Mon, 10 Jul 2023 09:52:36 +02:00 perf/ring_buffer: Use local_try_cmpxchg in __perf_output_begin Use local_try_cmpxchg instead of local_cmpxchg (*ptr, old, new) =3D=3D old in __perf_output_begin. 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/20230708090048.63046-2-ubizjak@gmail.com --- kernel/events/ring_buffer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index a0433f3..fb1e180 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -191,9 +191,10 @@ __perf_output_begin(struct perf_output_handle *handle, =20 perf_output_get_handle(handle); =20 + offset =3D local_read(&rb->head); do { + head =3D offset; tail =3D READ_ONCE(rb->user_page->data_tail); - offset =3D head =3D local_read(&rb->head); if (!rb->overwrite) { if (unlikely(!ring_buffer_has_space(head, tail, perf_data_size(rb), @@ -217,7 +218,7 @@ __perf_output_begin(struct perf_output_handle *handle, head +=3D size; else head -=3D size; - } while (local_cmpxchg(&rb->head, offset, head) !=3D offset); + } while (!local_try_cmpxchg(&rb->head, &offset, head)); =20 if (backward) { offset =3D head;