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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 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 1E93FC433B4 for ; Tue, 6 Apr 2021 00:18:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DEBFE613E8 for ; Tue, 6 Apr 2021 00:18:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242955AbhDFASS (ORCPT ); Mon, 5 Apr 2021 20:18:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:32876 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241600AbhDFASR (ORCPT ); Mon, 5 Apr 2021 20:18:17 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 91602613DF; Tue, 6 Apr 2021 00:18:09 +0000 (UTC) Date: Mon, 5 Apr 2021 20:18:07 -0400 From: Steven Rostedt To: Waiman Long Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Bharata B Rao , Phil Auld , Daniel Thompson , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] sched/debug: Use sched_debug_lock to serialize use of cgroup_path[] only Message-ID: <20210405201807.4ee7778d@gandalf.local.home> In-Reply-To: <20210405234203.23526-1-longman@redhat.com> References: <20210405234203.23526-1-longman@redhat.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 5 Apr 2021 19:42:03 -0400 Waiman Long wrote: > +/* > + * All the print_cpu() callers from sched_debug_show() will be allowed > + * to contend for sched_debug_lock and use group_path[] as their SEQ_printf() > + * calls will be much faster. However only one print_cpu() caller from > + * sysrq_sched_debug_show() which outputs to the console will be allowed > + * to use group_path[]. Another parallel console writer will have to use > + * a shorter stack buffer instead. Since the console output will be garbled > + * anyway, truncation of some cgroup paths shouldn't be a big issue. > + */ > +#define SEQ_printf_task_group_path(m, tg, fmt...) \ > +{ \ > + unsigned long flags; \ > + int token = m ? TOKEN_NA \ > + : xchg_acquire(&console_token, TOKEN_NONE); \ > + \ > + if (token == TOKEN_NONE) { \ > + char buf[128]; \ > + task_group_path(tg, buf, sizeof(buf)); \ > + SEQ_printf(m, fmt, buf); \ > + } else { \ > + spin_lock_irqsave(&sched_debug_lock, flags); \ > + task_group_path(tg, group_path, sizeof(group_path)); \ > + SEQ_printf(m, fmt, group_path); \ > + spin_unlock_irqrestore(&sched_debug_lock, flags); \ > + if (token == TOKEN_ACQUIRED) \ > + smp_store_release(&console_token, token); \ > + } \ > } > #endif And you said my suggestion was complex! I'll let others review this. -- Steve