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=-5.3 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 2AD57C433B4 for ; Wed, 14 Apr 2021 14:10:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0861F61220 for ; Wed, 14 Apr 2021 14:10:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233419AbhDNOKw (ORCPT ); Wed, 14 Apr 2021 10:10:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:58458 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232646AbhDNOKn (ORCPT ); Wed, 14 Apr 2021 10:10:43 -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 E185761166; Wed, 14 Apr 2021 14:10:20 +0000 (UTC) Date: Wed, 14 Apr 2021 10:10:19 -0400 From: Steven Rostedt To: Daniel Bristot de Oliveira Cc: linux-kernel@vger.kernel.org, kcarcia@redhat.com, Jonathan Corbet , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Alexandre Chartre , Clark Willaims , John Kacur , Juri Lelli , linux-doc@vger.kernel.org Subject: Re: [RFC PATCH 1/5] tracing/hwlat: Add a cpus file specific for hwlat_detector Message-ID: <20210414101019.7c5a66f6@gandalf.local.home> In-Reply-To: <94bbcd0e0f06b79aeb775e8dbf3a301f6679bb4c.1617889883.git.bristot@redhat.com> References: <94bbcd0e0f06b79aeb775e8dbf3a301f6679bb4c.1617889883.git.bristot@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 Thu, 8 Apr 2021 16:13:19 +0200 Daniel Bristot de Oliveira wrote: > Provides a "cpus" interface to the hardware latency detector. By > default, it lists all CPUs, allowing hwlatd threads to run on any online > CPU of the system. > > It serves to restrict the execution of hwlatd to the set of CPUs writing > via this interface. Note that hwlatd also respects the "tracing_cpumask." > Hence, hwlatd threads will run only on the set of CPUs allowed here AND > on "tracing_cpumask." > > Why not keep just "tracing_cpumask"? Because the user might be interested > in tracing what is running on other CPUs. For instance, one might run > hwlatd in one HT CPU while observing what is running on the sibling HT > CPU. The cpu list format is also more intuitive. > > Also in preparation to the per-cpu mode. OK, I'm still not convinced that you couldn't use tracing_cpumask here. Because we have instances, and tracing_cpumask is defined per instance, you could simply do: # cd /sys/kernel/tracing # mkdir instances/hwlat # echo a > instances/hwlat/tracing_cpumask # echo hwlat > instances/hwlat/current_tracer Now the tracing_cpumask above only affects the hwlat tracer. I'm just reluctant to add more tracing files if the current ones can be used without too much trouble. For being intuitive, let's make user space tools hide the nastiness of the kernel interface ;-) -- Steve