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=-18.8 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,USER_AGENT_GIT autolearn=ham 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 BBB48C2B9F7 for ; Fri, 28 May 2021 16:16:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90F1C613EB for ; Fri, 28 May 2021 16:16:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235920AbhE1QRl (ORCPT ); Fri, 28 May 2021 12:17:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57106 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235908AbhE1QRk (ORCPT ); Fri, 28 May 2021 12:17:40 -0400 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BD955C061574 for ; Fri, 28 May 2021 09:16:05 -0700 (PDT) Received: by mail-pl1-x636.google.com with SMTP id q16so1859231pls.6 for ; Fri, 28 May 2021 09:16:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=0AesoJC8dwORvJZMJlCBYhqk7Et+XhC6wlAE9oBGZmU=; b=BNXlCVIv2yFGtr4/5VcBsHUBS2FUvwvMCBbr83tzJOADVrNRwJT3qG9QbbauwZsa8N lL9oJx+4kgTstdtKP2uGfkK/4cF/valjhPq9GUC61cxGP8xE5IzliKNVw1LEtjibvEwc onD/pkaMmPlH1pHZhtNIY/6OyMVI/Ln1WeX8qXdHlrPYcgLHtAcKNTupIfGXTHAMZFdy ksb4/tAItKPY01+c97xaNU8jjlKgWiFMffVFhMLKTsVdmVKrs0PvHYmvHRK1OvktOgQB tqlQuxXtpsGxnTGnY3/l3oaNve7p1749MDSqPlx38u6gJ/6DZ9r2azPE90FmhhDQ6phi 14xg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=0AesoJC8dwORvJZMJlCBYhqk7Et+XhC6wlAE9oBGZmU=; b=injMA90hdfE0lK0LhtP3t2wrePgSpn4d2ZE7KcfeqAkpI4iKD6JglEBTsdx0lTZwVy T35ZxqyS6q4kht6FSx82jbtTkQH/CAb0IEGjbQGigaWt9vr9KfaX8UwNFkAK1whrTNYI qLECV/WDU6WoQPPyMg4U07ZjrykeON+0caJNUwjOnXoal1YgiHRxkPFNUp1GJ5dayWtw ve1ZI50Bc9NjkfF8hzWF2TTQsFMBhFEh37ygoUGlzVgy4SwhX3TZNsH5JYQSUM9tNHGR PeLEgJwCaMGRqmwqfU05QLHhzmKykWdaGIBTXgwieOOyMkfJzL1l9KH+bUQf7h/OhPmY /1OQ== X-Gm-Message-State: AOAM530TgfEZGC9Ci0rs3cOO6r7OnoHIslJPIxarwC69U+Tm2o619iqd kmfyFHXUxmaQUIk2PCrhHwu94Q== X-Google-Smtp-Source: ABdhPJz3sQx7BOFbfTjpVcSP7iMwnq4OEB+6a7He3sKx3CCRW9+RzFVmw36Z/fxwU+MxNrYLviZu8A== X-Received: by 2002:a17:902:d88e:b029:ff:1df8:f8b8 with SMTP id b14-20020a170902d88eb02900ff1df8f8b8mr7095746plz.4.1622218565185; Fri, 28 May 2021 09:16:05 -0700 (PDT) Received: from localhost ([103.207.71.35]) by smtp.gmail.com with ESMTPSA id u8sm4775604pgg.51.2021.05.28.09.16.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 May 2021 09:16:04 -0700 (PDT) From: Leo Yan To: Arnaldo Carvalho de Melo , Mathieu Poirier , Suzuki K Poulose , Mike Leach , Alexander Shishkin , John Garry , Will Deacon , Peter Zijlstra , Ingo Molnar , Jiri Olsa , Namhyung Kim , Daniel Kiss , Denis Nikitin , coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Cc: Leo Yan Subject: [PATCH v1 1/3] coresight: etm-perf: Correct buffer syncing for snapshot Date: Sat, 29 May 2021 00:15:50 +0800 Message-Id: <20210528161552.654907-2-leo.yan@linaro.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210528161552.654907-1-leo.yan@linaro.org> References: <20210528161552.654907-1-leo.yan@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org The perf tool records the Arm CoreSight trace data with snapshot mode with the option '-S', when receiving USR2 signal, it is observed the captured trace data size is very varied: from several MBs to ~20MBs. This can be reproduced with the command: perf record -e cs_etm// -S \ -- dd if=/dev/zero of=/dev/null > /dev/null 2>&1 & PERFPID=$! sleep 1 kill -USR2 $PERFPID It's different for only specifying option '-S' than options '-a -S'. If without option '-a', perf tool creates separate AUX buffers for every CPU, but the tracer will be enabled only when the profiled program is scheduled onto the corresponding CPU, this might lead to record very old trace data when snapshot. Let's see below diagram: snapshot CPU0: ______###P1###__________________________________________| CPU1: __________________________###P3###____________###P5###__| CPU2: ____________________________________###P4###____________| CPU3: ________________###P2###________________________________V In this diagram, the program runs for 5 periods (from P1 to P5), these 5 periods show the task run on different CPUs, e.g. during P1 period the program runs on CPU0, and during P2 period the program is migrated to CPU1, and so on. At the end of P1 period when the program is switched out from CPU0, the ETR trace data is saved into AUX trace buffer, this AUX buffer is a dedicated buffer for CPU0's tracer. With the same logic, P2's trace data is saved into CPU3's tracer buffer, P4's trace data is saved into CPU2's buffer, P3 and P5's trace data is saved into CPU1's. Therefore, when snapshot, it saves the trace data from all AUX ring buffers (in this case, it have total 4 AUX ring buffers) into perf data file. This is why we can see varied trace data size, it's quite dependent on the task scheduling on CPUs, if the task is spinned to only one CPU and without scheduling out, it will only record trace data from only one AUX trace buffer. If the task is frequently scheduled in and out, then it gives more chance to fill trace data into the AUX buffer. In this example, it also causes the discontinuous trace data. If P3's trace data is lost after P5's trace data overwrites the AUX trace data, thus perf tool fails to record continuous trace data if only have trace data for P1/P2/P4/P5. For snapshot mode, usually the user only wants to capture the trace data for the specific time point and prior to the that point the tracer should work with free run mode. This means it's not necessary to capture trace data for task's scheduling in and out until the perf tool explicitly disables tracers for snapshot. This can be fulfilled by checking the variable "event->ctx->is_active", when the task is scheduled out this variable is set to zero, and when snapshot this variable is still non-zero value. So the driver can only record trace data only when "event->ctx->is_active" is non-zero. After applying this change, the perf tool can record the consistent trace data size for snapshot. Signed-off-by: Leo Yan --- .../hwtracing/coresight/coresight-etm-perf.c | 30 +++++++++++++++++-- .../hwtracing/coresight/coresight-etm-perf.h | 2 ++ 2 files changed, 29 insertions(+), 3 deletions(-) diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c index 6f398377fec9..fd36d0530087 100644 --- a/drivers/hwtracing/coresight/coresight-etm-perf.c +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c @@ -284,6 +284,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages, if (!event_data) return NULL; INIT_WORK(&event_data->work, free_event_data); + event_data->overwrite = overwrite; /* First get the selected sink from user space. */ if (event->attr.config2) { @@ -517,9 +518,32 @@ static void etm_event_stop(struct perf_event *event, int mode) if (!sink_ops(sink)->update_buffer) return; - size = sink_ops(sink)->update_buffer(sink, handle, - event_data->snk_config); - perf_aux_output_end(handle, size); + /* + * In the snapshot mode, if only specifies option '-S' (note, + * user doesn't specify option '-a' in this case), the AUX ring + * buffers are allocated for every CPU but the AUX trace is + * recorded in per-thread mode. In this mode, it's needless to + * save AUX trace data into the AUX ring buffer when the + * profiled program is scheduled out from a CPU, alternatively, + * the driver should only capture AUX trace data when the perf + * tool receives USR2 signal for taking snapshot. + * + * The variable "event->ctx->is_active" can be used to + * distinguish the cases between the program scheduling out and + * snapshot: its value is zero when the profiled task scheduled + * out, and it is a non-zero value when perf tool invokes ioctl + * PERF_EVENT_IOC_DISABLE for snapshot. + * + * Only updates AUX ring buffer for snapshot, or for the perf + * session which is not in snapshot mode. + */ + if (!event_data->overwrite || event->ctx->is_active) { + size = sink_ops(sink)->update_buffer(sink, handle, + event_data->snk_config); + perf_aux_output_end(handle, size); + } else { + perf_aux_output_end(handle, 0); + } } /* Disabling the path make its elements available to other sessions */ diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.h b/drivers/hwtracing/coresight/coresight-etm-perf.h index 3e4f2ad5e193..2cc3af05495f 100644 --- a/drivers/hwtracing/coresight/coresight-etm-perf.h +++ b/drivers/hwtracing/coresight/coresight-etm-perf.h @@ -49,12 +49,14 @@ struct etm_filters { * @mask: Hold the CPU(s) this event was set for. * @snk_config: The sink configuration. * @path: An array of path, each slot for one CPU. + * @overwrite: Flag for snapshot mode. */ struct etm_event_data { struct work_struct work; cpumask_t mask; void *snk_config; struct list_head * __percpu *path; + bool overwrite; }; #if IS_ENABLED(CONFIG_CORESIGHT) -- 2.25.1