From nobody Sun Feb 8 12:37:09 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 3DD9BC6FD1F for ; Wed, 22 Mar 2023 18:43:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230443AbjCVSnz (ORCPT ); Wed, 22 Mar 2023 14:43:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56094 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230026AbjCVSnj (ORCPT ); Wed, 22 Mar 2023 14:43:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4185C23A75 for ; Wed, 22 Mar 2023 11:43:37 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id BEA3962284 for ; Wed, 22 Mar 2023 18:43:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99F1CC433EF; Wed, 22 Mar 2023 18:43:36 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.96) (envelope-from ) id 1pf3Qt-000pbL-2O; Wed, 22 Mar 2023 14:43:35 -0400 Message-ID: <20230322184335.558195206@goodmis.org> User-Agent: quilt/0.66 Date: Wed, 22 Mar 2023 14:42:49 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Andrew Morton , Uros Bizjak , Mukesh Ojha Subject: [for-next][PATCH 10/11] ring_buffer: Use try_cmpxchg instead of cmpxchg References: <20230322184239.594953818@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Uros Bizjak Use try_cmpxchg instead of 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. Link: https://lkml.kernel.org/r/20230305155532.5549-4-ubizjak@gmail.com Cc: Masami Hiramatsu Signed-off-by: Uros Bizjak Acked-by: Mukesh Ojha Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 93f854433d89..2d5c3caff32d 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4057,10 +4057,10 @@ void ring_buffer_record_off(struct trace_buffer *bu= ffer) unsigned int rd; unsigned int new_rd; =20 + rd =3D atomic_read(&buffer->record_disabled); do { - rd =3D atomic_read(&buffer->record_disabled); new_rd =3D rd | RB_BUFFER_OFF; - } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) !=3D rd); + } while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd)); } EXPORT_SYMBOL_GPL(ring_buffer_record_off); =20 @@ -4080,10 +4080,10 @@ void ring_buffer_record_on(struct trace_buffer *buf= fer) unsigned int rd; unsigned int new_rd; =20 + rd =3D atomic_read(&buffer->record_disabled); do { - rd =3D atomic_read(&buffer->record_disabled); new_rd =3D rd & ~RB_BUFFER_OFF; - } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) !=3D rd); + } while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd)); } EXPORT_SYMBOL_GPL(ring_buffer_record_on); =20 --=20 2.39.1