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 76F70C64E7B for ; Thu, 3 Dec 2020 06:42:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20A4B20709 for ; Thu, 3 Dec 2020 06:42:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729792AbgLCGmn (ORCPT ); Thu, 3 Dec 2020 01:42:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52302 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726405AbgLCGmn (ORCPT ); Thu, 3 Dec 2020 01:42:43 -0500 Received: from mail-pg1-x52d.google.com (mail-pg1-x52d.google.com [IPv6:2607:f8b0:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 29720C061A4E for ; Wed, 2 Dec 2020 22:42:03 -0800 (PST) Received: by mail-pg1-x52d.google.com with SMTP id o4so833015pgj.0 for ; Wed, 02 Dec 2020 22:42:03 -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=Fjhcv6RFP/GUwmukcAhw/NTkSL23rOfX91aQcDsRbok=; b=kgxpaOnsST0YHmPUrZ6KCzDTi638kpNhRLe7BUNLNHBfIKxEia0PEaHVKSlAqXdKQX 7ZuO5LDCjmCTunKLx+O1yV5b5kCZoSUEFBhSplhFAceFDnljTvBg93Hgi4wuJDno0ncP 55BP99NhLVACNViHaqMLh62fF+qcJCYLZpVRv0T84qc6BaXkbiIB5ysCzL/EJPQ7ub1V 03jxqpUSiqqUEZRc4Av7p5VlWGVYG5c8CG28/Nl0mcCIibJe2HfLPQsRZWl9wEteLZg0 IVRz6UoaGeWGXvRYzrL/ZQv/Mt67jSxX40559f0extLbK/xL6lelD9Oh7ETJPbVpiPri LbCA== 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=Fjhcv6RFP/GUwmukcAhw/NTkSL23rOfX91aQcDsRbok=; b=GyFboSPWMDqdAdGC76CLj1VI4u50hULAcn30jdq2PW7d010VN0rEs9P75i0PuPxD9r nkjX/DljlTjhWZpopwzM5MEFSgR8MENfAoXGx9wlMi0s0UJ4nUUwg7xmU3YOQSpVsoL+ 4M3P1SuiDG0HxSpCrjnPlq1B4tAGdbZrVPoBiU11xRcaWP5ix8rkwctTMgzDZKWfpOGW TjNX6aFIyjfp2BunVI5k+RUAg2U1C2KfcwrOCUUdbk2IJZzLBsw0MNZpDs8fmD1zYHoJ j9uYJSqgBXoSjc22TfSiyYoC73uv98rAYdTJeFQ75xCGwkXixoXhheXfd4Nbs8KAqbxH beRQ== X-Gm-Message-State: AOAM531hyLQVW97lJsCYsblFfa1tes3WFt+A1MvRcArVlmNH4MdxQED2 O2VAfoG4JWs1a5UdRcZ8fHktGA== X-Google-Smtp-Source: ABdhPJxXeRSBVsO+UeuhLh5avxTnY3X0SrcIbPxswt3/8g7/sun3+w7roRua3kUheQQDAoUzZCmmYg== X-Received: by 2002:a63:7cf:: with SMTP id 198mr1830564pgh.453.1606977722392; Wed, 02 Dec 2020 22:42:02 -0800 (PST) Received: from leoy-ThinkPad-X240s ([202.131.71.236]) by smtp.gmail.com with ESMTPSA id q19sm498218pff.101.2020.12.02.22.41.59 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Wed, 02 Dec 2020 22:42:01 -0800 (PST) Date: Thu, 3 Dec 2020 14:41:57 +0800 From: Leo Yan To: Will Deacon , Mathieu Poirier 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: <20201203064157.GF28939@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> <20201203063941.GE28939@leoy-ThinkPad-X240s> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201203063941.GE28939@leoy-ThinkPad-X240s> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Looping in Mathieu at this time. On Thu, Dec 03, 2020 at 02:39:41PM +0800, Leo Yan wrote: > 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