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=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 98CC4C63777 for ; Thu, 3 Dec 2020 06:40:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47870206B6 for ; Thu, 3 Dec 2020 06:40:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725984AbgLCGk3 (ORCPT ); Thu, 3 Dec 2020 01:40:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbgLCGk3 (ORCPT ); Thu, 3 Dec 2020 01:40:29 -0500 Received: from mail-pl1-x629.google.com (mail-pl1-x629.google.com [IPv6:2607:f8b0:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 17F85C061A4D for ; Wed, 2 Dec 2020 22:39:49 -0800 (PST) Received: by mail-pl1-x629.google.com with SMTP id s2so582480plr.9 for ; Wed, 02 Dec 2020 22:39:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=p90ZTrcODaMIh1PUcjXTtSOF3aHh5Iqv2c9lQCLd5uw=; b=mQlNuueE54XSMWq6SP8fFDIEQPOEDPETEey3dENLqhob4IP0rwSDaMWufXPbwQrTy5 DfOrJG0MoN015zDuWdAoZ4n0MZyPwbYHfBWIKxRgyAUBU8n1e0wiQO1R+V7ZpQmTwAEx Dv4qJX6AA5LkzCGWlZJt2qIot4zzQBc8GU68zXp4UDW6ZK01adsFGAIjkUQMLlNpuBRr eO3/jXso0XELDb0aW38cbsWgQVhK175ctbxvqRBykQYaE45dzfpt/UoIGjViFAY404Dq XzE3KsYbpByBOeAmpCl4EtATdsHpDQQcly+6UBNE16+Jp/Q2yirUSTKopr+zqgNnwDY5 cTng== 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:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=p90ZTrcODaMIh1PUcjXTtSOF3aHh5Iqv2c9lQCLd5uw=; b=pFGFk9RRnGXL6nPq5HUuKCoedWLc7OXqC5cBDLlK2Vgm/yxRuXI7fN8C0vIwRTThJX ZVdY2u/pywl1Vjpq1M42PyWzRJmLnOTI4vF5p/KQMZ9lqpJm8rD+Za0GkXWM65HmKz79 mLk4frLP4h+n6tNsEdoxtq4Tx2o54XU1zvJ3PA9Hy5mEn/n63xJMLTQ6UXrZkACrWbW6 OFV1y0aj99lBkW3RUf+VVCqjeXtQiHx8VEmreRs+4Wiz12ViJn6DyVmvkFw6/8hhim+s vsXIExLJKUg8UEacaR2sLcZeqjVQDpJDBwHLKLA8fXzkSP363aux8/fKYhJFDNWFFiJy sPjA== X-Gm-Message-State: AOAM532dgOJL2s47y+0XMAoOXprS61+26F1RI0TQCrc4i/8jLT+4pQT8 kSZb57iiXZP1aw9fGqh6aOtG5A== X-Google-Smtp-Source: ABdhPJyOoElyxwiAEuD0omkoyT6H/99s9lIaMAXnW6c09Gjnn8aUkR6r+ju4a9dxwk4XRIAiskjs6A== X-Received: by 2002:a17:902:b498:b029:da:84a7:be94 with SMTP id y24-20020a170902b498b02900da84a7be94mr1731127plr.52.1606977588537; Wed, 02 Dec 2020 22:39:48 -0800 (PST) Received: from leoy-ThinkPad-X240s ([202.155.204.36]) by smtp.gmail.com with ESMTPSA id j10sm306546pji.29.2020.12.02.22.39.45 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Wed, 02 Dec 2020 22:39:47 -0800 (PST) Date: Thu, 3 Dec 2020 14:39:41 +0800 From: Leo Yan To: Will Deacon Cc: James Clark , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Mark Rutland , Al Grant , John Garry , Suzuki K Poulose Subject: Re: [PATCH] drivers/perf: Enable PID_IN_CONTEXTIDR with SPE Message-ID: <20201203063941.GE28939@leoy-ThinkPad-X240s> References: <20201130162454.28255-1-james.clark@arm.com> <20201130164650.GA25187@willie-the-truck> <20201201041040.GC28939@leoy-ThinkPad-X240s> <20201201230935.GD28496@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201201230935.GD28496@willie-the-truck> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Hi Will, [ + Mathieu ] On Tue, Dec 01, 2020 at 11:09:36PM +0000, Will Deacon wrote: > On Tue, Dec 01, 2020 at 12:10:40PM +0800, Leo Yan wrote: > > On Mon, Nov 30, 2020 at 04:46:51PM +0000, Will Deacon wrote: > > > On Mon, Nov 30, 2020 at 06:24:54PM +0200, James Clark wrote: > > > > Enable PID_IN_CONTEXTIDR by default when Arm SPE is enabled. > > > > This flag is required to get PID data in the SPE trace. Without > > > > it the perf tool will report 0 for PID which isn't very useful, > > > > especially when doing system wide profiling or profiling > > > > applications that fork. > > > > > > Can perf not figure out the pid some other way? (e.g. by tracing context > > > switches and correlating that with the SPE data?). > > > > For perf 'per-thread' mode, we can use context switch trace event as > > assisted info to select thread context. But for "system wide" mode and > > "snapshot" mode in perf tool, since the trace data is continuous, I > > think we cannot use context switch trace event to correlate the SPE > > trace data. > > Is there no way to correlate them with something like CNTVCT? Good point. Yes, we can convert CNTVCT to system time; I read the code in the perf's intel-pt.c and found the timestamp is used to correlate the auxtrace heap. I think it's better to dig more for detailed implementation. > > > Also, how does this work with pid namespaces? > > > > Here we are studying the implemetation of Intel-PT and Arm CoreSight. > > > > The context ID is stored into the hardware trace data when record; > > afterwards when perf tool decodes the trace data and detects the > > packet for context ID, it will select the machine's thread context in > > perf [1]. Since the perf tool gathers all the threads infomation in > > perf data file, based on the context ID, it can find the corresponding > > thread pointer with function machine__find_thread() [2]. > > > > Since your question is for "pid namespace", to be honest, I don't know > > how perf tool to handle any confliction for differrent processes share > > the same PID, and I am not sure if you are asking CGroup related stuff > > or not. If this cannot answer your question, please let me know. > > My point was that the pid value written to CONTEXTIDR is a global pid > and does not take namespacing into account. If perf is run inside a pid > namespace, it will therefore not work. Understand now. The perf events PERF_RECORD_ITRACE_START/PERF_RECORD_SWITCH/ PERF_RECORD_SWITCH_CPU_WIDE can be used to set pid/tid in perf. So this would be a safe way for perf tool running in pid namespace. Loop in Mathieu, this is a common issue for both Arm SPE and CoreSight (IIRC, though CoreSight's timestamp is not strictly attaching to Arm arch timer counter, the trend is to unify this for using arch timer counter). I think James could continue to upstream a new patch by following your suggestion for enabling PID_IN_CONTEXTIDR, eventually, it's a feature for Arm SPE to record CONTEXTIDR in its packet. Your questions inspired me, thanks! Leo