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=-9.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 59F69C64E7A for ; Tue, 1 Dec 2020 23:10:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F23E82220B for ; Tue, 1 Dec 2020 23:10:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726167AbgLAXKW (ORCPT ); Tue, 1 Dec 2020 18:10:22 -0500 Received: from mail.kernel.org ([198.145.29.99]:46316 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726082AbgLAXKW (ORCPT ); Tue, 1 Dec 2020 18:10:22 -0500 Date: Tue, 1 Dec 2020 23:09:36 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1606864181; bh=R1LZxKhC63MgOhIWSKRcfmgG/w02ZOoz7xHqWe+Pr7k=; h=From:To:Cc:Subject:References:In-Reply-To:From; b=zsaqQBCXac4ssa46wKGJrHjx78Yx+BKPCLV22+wvuO2lvTanFDGUxj+NCPAd7BT2E TQo1DGLBSM79hGhonz/V0LYXVbogx5ZAv/HDAPU3QyZI4crCjRZPDk3x8CH2QsIBsJ 5osHzXr+wQYAdBUuuOnHChySkw+W5DZWwAQdrdJ8= From: Will Deacon To: Leo Yan 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: <20201201230935.GD28496@willie-the-truck> References: <20201130162454.28255-1-james.clark@arm.com> <20201130164650.GA25187@willie-the-truck> <20201201041040.GC28939@leoy-ThinkPad-X240s> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201201041040.GC28939@leoy-ThinkPad-X240s> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org 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? > > 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. Will