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=-7.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 BD109C64E7A for ; Tue, 1 Dec 2020 23:11:01 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 55958221FF for ; Tue, 1 Dec 2020 23:11:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 55958221FF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=H+vjA7qrcj8lgmOomHfWSEMLKS7YI+8r5YBdOcmggrY=; b=nvhHsWRwXiUZx36OPH7ZW3xuD aw/0mvarbcNJOtgQ1BnUvumrCJs5z8EvVKB6BR43Jty/8jDXKs6e1pcqOXFtxvr8AeFxhy3FPS9Vk G3QZ2mLJqjnX6nIy4RBnKkg37CUmLqjKJR4r8ZSzssqBD5zyKPFso6+JyJ+v8R1ONZdR2wAPHNxQn linON9I9g682XLibVsH47ivP+ZWJ9tk22IALgMF5w1PJk6ugOnlur4Yx6OELGO/V0IgvRuDgnFH8S AAHZtT34eRBi+M+T/vI2x+PPp7iyasx5W/ELZ35KWV3viHjJqF1vMFSF27bTvGwHNoBP1fufL5qly K/S4AZS9A==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkEmH-000334-Hr; Tue, 01 Dec 2020 23:09:45 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkEmE-00032c-VR for linux-arm-kernel@lists.infradead.org; Tue, 01 Dec 2020 23:09:43 +0000 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 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-Disposition: inline In-Reply-To: <20201201041040.GC28939@leoy-ThinkPad-X240s> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201201_180943_154492_8DD63919 X-CRM114-Status: GOOD ( 21.91 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Al Grant , Suzuki K Poulose , John Garry , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, James Clark , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel