From mboxrd@z Thu Jan 1 00:00:00 1970 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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9B11CC6FA8E for ; Sun, 5 Mar 2023 21:06:44 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4PVDm317Ygz3fjT for ; Mon, 6 Mar 2023 08:06:43 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20210112 header.b=AzC0MtpS; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=gmail.com (client-ip=2a00:1450:4864:20::52e; helo=mail-ed1-x52e.google.com; envelope-from=ubizjak@gmail.com; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20210112 header.b=AzC0MtpS; dkim-atps=neutral Received: from mail-ed1-x52e.google.com (mail-ed1-x52e.google.com [IPv6:2a00:1450:4864:20::52e]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4PVDY159Fhz3cLB for ; Mon, 6 Mar 2023 07:57:09 +1100 (AEDT) Received: by mail-ed1-x52e.google.com with SMTP id a25so31042001edb.0 for ; Sun, 05 Mar 2023 12:57:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1678049829; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=xOf0dR/RPpY4HJc+yEr00P2lL8nnE6ZdPZ2RnMEV2qQ=; b=AzC0MtpS6jzuzYUPFsrIfgSP8aZbYwDqq5a+izUb9a0flhuTk9IJhffPMtswIUk4wO sg+KQDUeI1WfTBjEPCVkavJWGZOiRXkonvodFjQekv1AtQJNs5CNYgKk72i8myvpgGVe K9+Gcl430QJD9AbzGRenEZ61TH0KIeWK+0iYs+J05wVbAMYgv5sIn3w1+Cwy1JerQSRC KH89b71gdC8EcpGw2scdHdGW+tPap0uAwmnq+3aLE3kGWG2fm1xZDaMDvjLA9woC5Ulu 0/MPaQHFdc8LJgoZ7thFoEH3DKdiynUC63aS/FSnJG4o6I/92Na/lIc5Pd1rCjK+C5wU iyIg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678049829; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=xOf0dR/RPpY4HJc+yEr00P2lL8nnE6ZdPZ2RnMEV2qQ=; b=lmU88tql53HzSHEcU72hpEM8tYgPqyKmfFg5Ze3Q/g0Xw9HnOy5vM6SVfw/iymdRJr i2a4ibRKxJFKR2VBusCxkEqZ6SwLQjBYu3np9xR3yyYWsmVlM5+6ykFR/vbTtlA9VSOH rBNGeQY6vo2NbktZNtu8POjTS8LWGq3FcAHatgY1zEPCm8gOcDNl+FyLs+MweXA60zur TxtCCCjBE0Lq8GPGIw82nAWrvm4pUwcDb1kUjFEmkEcesXZloR9mm8haUKxE8/Oh7Fnw Jed6oPwstRnRgquc/iQj9ah7H0gjIMFDtU3oq/t+XETs+RXHfEFtVWIn2x48Kj07UEcB P6Tg== X-Gm-Message-State: AO0yUKX97DmEF6CUrmTZg1SyFSmIwmBbSyWxcqvNREWiR3iP4qqZm4mp ijwWOg4oOQpDpBT6+xL8BII= X-Google-Smtp-Source: AK7set89glUReQEBerTf3N2tzQKZj5f2Ne8jws0vz8p+B9w+amQ0mlW3rs5ChgaK3OjP1RYo4BNMlQ== X-Received: by 2002:a17:906:36d3:b0:8bf:e95c:467b with SMTP id b19-20020a17090636d300b008bfe95c467bmr7987952ejc.63.1678049829092; Sun, 05 Mar 2023 12:57:09 -0800 (PST) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id ay24-20020a170906d29800b0090953b9da51sm3615436ejb.194.2023.03.05.12.57.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Mar 2023 12:57:08 -0800 (PST) From: Uros Bizjak To: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: [PATCH 10/10] perf/ring_buffer: use local_try_cmpxchg in __perf_output_begin Date: Sun, 5 Mar 2023 21:56:28 +0100 Message-Id: <20230305205628.27385-11-ubizjak@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230305205628.27385-1-ubizjak@gmail.com> References: <20230305205628.27385-1-ubizjak@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Ian Rogers , Peter Zijlstra , Uros Bizjak , Arnaldo Carvalho de Melo , Alexander Shishkin , Ingo Molnar , Jiri Olsa , Namhyung Kim Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Use local_try_cmpxchg instead of local_cmpxchg (*ptr, old, new) == old in __perf_output_begin. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg. Also, local_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: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Cc: Mark Rutland Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Namhyung Kim Cc: Ian Rogers Signed-off-by: Uros Bizjak --- 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 273a0fe7910a..e07c10f4d141 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, perf_output_get_handle(handle); + offset = local_read(&rb->head); do { + head = offset; tail = READ_ONCE(rb->user_page->data_tail); - offset = head = 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 += size; else head -= size; - } while (local_cmpxchg(&rb->head, offset, head) != offset); + } while (!local_try_cmpxchg(&rb->head, &offset, head)); if (backward) { offset = head; -- 2.39.2