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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0274C432BE for ; Sun, 29 Aug 2021 10:51:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A226C60F4B for ; Sun, 29 Aug 2021 10:51:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235145AbhH2Kwf (ORCPT ); Sun, 29 Aug 2021 06:52:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235019AbhH2Kwc (ORCPT ); Sun, 29 Aug 2021 06:52:32 -0400 Received: from mail-pj1-x1032.google.com (mail-pj1-x1032.google.com [IPv6:2607:f8b0:4864:20::1032]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 66213C061575 for ; Sun, 29 Aug 2021 03:51:40 -0700 (PDT) Received: by mail-pj1-x1032.google.com with SMTP id j4-20020a17090a734400b0018f6dd1ec97so7999612pjs.3 for ; Sun, 29 Aug 2021 03:51:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=lFzFG2XeopOOy6Mnz/fganlfwA/D8OqBSKpVQIaiZig=; b=z8B6S7DTFgi69OBaCjTUZIAvdGWjOqopBYd0e5b9wfD2TYtv2Yz7XF/0ZRYVqqNYTA aWoYGt03eFil1j1RR4ERTcZZ4ASU0Si4zjY5c7tC26ybatnYAC/mwwyYYif1XIpTpeKW JdoULIRhDxxRQcum/i3YpDF2O0uVsT87MeHqFMF4ilYgqX5g995JNn3uSkMNVEChUdBo 012nXR3PXMSqYj0q3rIPSC3rTvoKbxZPI9hcwAeVI53GvfrBV6JZS2QRb508mW3YiNHT so9SNsPLO9MSMM+LCVhZ8o3odbtaprHf/TkbuRcA6e+b3I6MMoKanzWdbgFceCXVd55T WFYQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=lFzFG2XeopOOy6Mnz/fganlfwA/D8OqBSKpVQIaiZig=; b=eA/29JQzLgyPWIZXqcdLFDG6ARffZNJ4C5FfGEQHL2Nh4noU9NWCgiEluiAiDrSzDh VXSh/LaMU+Jki0VqfnVVVzRLwHn4QzJr0MxHKeqg2E9LbrSqrvQbWkxqNPbq7rXxTh5U GjuiJmXmawf5hsor9wjb1AF89Lm51MumEM5q6Tj+H4n+ntCvEsylcq0FVQr8hyoSQhnV Sr6Afq5mIll1GwM33o3BngYMEQt8dVZpJ4xsW4e3Fe0jVIAOP4O4KEjffWmqOQ7j3QSE AhZKq8JBZKy1BNBqE/JCq17HoMNya374Eij6NaQK4VmUBz3CLXhn5AIrFOROVF3dCwgu 8XBg== X-Gm-Message-State: AOAM532NyJqjGJiPj7iXeM6vjnHtywboKIWPaNWnw6JbyeuVJQRhvYof eqntEQnx6ew36Hd+9+PDLh8IYQ== X-Google-Smtp-Source: ABdhPJwjWsoF+6aTXesS8YJ625+DMN9GCiyDBwQ7qEmqcmLQGPVUk4SlInxmsMvfuMy9p1LbnGbAdg== X-Received: by 2002:a17:90b:3b82:: with SMTP id pc2mr20677208pjb.224.1630234299731; Sun, 29 Aug 2021 03:51:39 -0700 (PDT) Received: from leoy-ThinkPad-X240s ([134.195.101.46]) by smtp.gmail.com with ESMTPSA id 15sm7641004pjw.39.2021.08.29.03.51.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 29 Aug 2021 03:51:39 -0700 (PDT) Date: Sun, 29 Aug 2021 18:51:30 +0800 From: Leo Yan To: Arnaldo Carvalho de Melo , Peter Zijlstra , Adrian Hunter , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" , Mathieu Poirier , Suzuki K Poulose , Mike Leach , Michael Petlan , "Frank Ch. Eigler" , Song Liu , x86@kernel.org, Daniel =?iso-8859-1?Q?D=EDaz?= , Andrii Nakryiko , Alexei Starovoitov , Sedat Dilek , Andi Kleen , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, coresight@lists.linaro.org Subject: Re: [PATCH v5 1/9] perf/ring_buffer: Add comment for barriers on AUX ring buffer Message-ID: <20210829105130.GA14461@leoy-ThinkPad-X240s> References: <20210809111407.596077-1-leo.yan@linaro.org> <20210809111407.596077-2-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210809111407.596077-2-leo.yan@linaro.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On Mon, Aug 09, 2021 at 07:13:59PM +0800, Leo Yan wrote: > AUX ring buffer applies almost the same barriers as perf ring buffer, > but there has an exception for ordering between writing the AUX trace > data and updating user_page::aux_head. > > This patch adds comment for how to use the barriers on AUX ring buffer, > and gives comment to ask the drivers to flush the trace data into AUX > ring buffer prior to updating user_page::aux_head. > > Signed-off-by: Leo Yan > Acked-by: Peter Zijlstra (Intel) You have given the ACK tag before, could you pick up this patch? Thanks, Leo > --- > kernel/events/ring_buffer.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > index 52868716ec35..5cf6579be05e 100644 > --- a/kernel/events/ring_buffer.c > +++ b/kernel/events/ring_buffer.c > @@ -509,6 +509,15 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) > perf_event_aux_event(handle->event, aux_head, size, > handle->aux_flags); > > + /* > + * See perf_output_put_handle(), AUX ring buffer applies the same > + * barrier pairing as the perf ring buffer; except for B, since > + * AUX ring buffer is written by hardware trace, we cannot simply > + * use the generic memory barrier (like smp_wmb()) prior to update > + * user_page::aux_head, the hardware trace driver takes the > + * responsibility to ensure the trace data has been flushed into > + * the AUX buffer before calling perf_aux_output_end(). > + */ > WRITE_ONCE(rb->user_page->aux_head, rb->aux_head); > if (rb_need_aux_wakeup(rb)) > wakeup = true; > -- > 2.25.1 >