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=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 B097FC43387 for ; Thu, 3 Jan 2019 13:26:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8551F21479 for ; Thu, 3 Jan 2019 13:26:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731716AbfACN0f (ORCPT ); Thu, 3 Jan 2019 08:26:35 -0500 Received: from terminus.zytor.com ([198.137.202.136]:53455 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730107AbfACN0e (ORCPT ); Thu, 3 Jan 2019 08:26:34 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x03DQR6D1387436 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 3 Jan 2019 05:26:27 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x03DQRQh1387433; Thu, 3 Jan 2019 05:26:27 -0800 Date: Thu, 3 Jan 2019 05:26:27 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Adrian Hunter Message-ID: Cc: linux-kernel@vger.kernel.org, adrian.hunter@intel.com, jolsa@kernel.org, acme@redhat.com, tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com Reply-To: linux-kernel@vger.kernel.org, adrian.hunter@intel.com, jolsa@kernel.org, mingo@kernel.org, acme@redhat.com, tglx@linutronix.de, hpa@zytor.com In-Reply-To: <20181221120620.9659-9-adrian.hunter@intel.com> References: <20181221120620.9659-9-adrian.hunter@intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/urgent] perf session: Add comment for perf_session__register_idle_thread() Git-Commit-ID: b25756df5b28cd7b6e91200fc5012e7c76e8ec69 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: b25756df5b28cd7b6e91200fc5012e7c76e8ec69 Gitweb: https://git.kernel.org/tip/b25756df5b28cd7b6e91200fc5012e7c76e8ec69 Author: Adrian Hunter AuthorDate: Fri, 21 Dec 2018 14:06:20 +0200 Committer: Arnaldo Carvalho de Melo CommitDate: Wed, 2 Jan 2019 11:05:06 -0300 perf session: Add comment for perf_session__register_idle_thread() Add a comment to perf_session__register_idle_thread() to bring attention to a pitfall with the idle task thread structure. The pitfall is that there should really be a 'struct thread' for the idle task of each cpu, but there is only one that can have pid == tid == 0. Signed-off-by: Adrian Hunter Acked-by: Jiri Olsa Link: http://lkml.kernel.org/r/20181221120620.9659-9-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/session.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c index 78a067777144..5456c84c7dd1 100644 --- a/tools/perf/util/session.c +++ b/tools/perf/util/session.c @@ -1527,6 +1527,13 @@ struct thread *perf_session__findnew(struct perf_session *session, pid_t pid) return machine__findnew_thread(&session->machines.host, -1, pid); } +/* + * Threads are identified by pid and tid, and the idle task has pid == tid == 0. + * So here a single thread is created for that, but actually there is a separate + * idle task per cpu, so there should be one 'struct thread' per cpu, but there + * is only 1. That causes problems for some tools, requiring workarounds. For + * example get_idle_thread() in builtin-sched.c, or thread_stack__per_cpu(). + */ int perf_session__register_idle_thread(struct perf_session *session) { struct thread *thread;