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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 475F2C433F5 for ; Thu, 30 Sep 2021 15:49:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 244C661267 for ; Thu, 30 Sep 2021 15:49:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346334AbhI3Pvg (ORCPT ); Thu, 30 Sep 2021 11:51:36 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:50996 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346074AbhI3Pvf (ORCPT ); Thu, 30 Sep 2021 11:51:35 -0400 Date: Thu, 30 Sep 2021 17:49:50 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1633016992; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/pBBYaU8HcrLt7lPSLrbdU2c0rrQjLddlaRCbL5buVI=; b=yZyz4k7nMH2ku0KGjtAM0RfjOMjTVuUkBEzcjRorAVi3NECqjT0UWmd2g5lGDYYAkVXGYf FN9aN3am6yGh/fFAZcn816WQS3Qmrz7GYwbWLjolU5xdDFyw/ZNkxSh6Ov4/wTNCKucUrg qG4AhrT2liYPhGR8juXb7U/QCfE/dbrCx42RCrKcMQCRrelpJSuHBJSZmOOVEXreiUJNFE sT4TFY63mai7Ee9JCHV0QqyOdHzh3SRsfnNozxB2F69RZ2Lmv9XXQsdASl3dA9G+UwYcCJ LVC7B/kR0ym2pSLatxtJQ0vxWjsZjmBdXA25O0YKY7iWRA1U7ITKeTEFRIGYXQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1633016992; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/pBBYaU8HcrLt7lPSLrbdU2c0rrQjLddlaRCbL5buVI=; b=X2GQsF8lArkjTsphCQqc9fwuVu0E0Dmy4ageh9oOj3+TCFDmXCBvrNAfZeSXkTqiye7JIq /Qjwy0ywkZO8wWDg== From: Sebastian Andrzej Siewior To: John Ogness Cc: John Kacur , Punit Agrawal , Clark Williams , Pierre FICHEUX , linux-rt-users@vger.kernel.org, Thomas Gleixner Subject: Re: Strange problem with PREEMPT_RT Message-ID: <20210930154950.ucpjabqtdk2rig33@linutronix.de> References: <87y27e53a2.fsf@stealth> <20210930132319.eixnv6rb66ui6x6j@linutronix.de> <87v92i9o5t.fsf@jogness.linutronix.de> <6034cc70-fb69-d9d-ce31-673d4d42adc@redhat.com> <87pmsq9kdd.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87pmsq9kdd.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 2021-09-30 17:08:54 [+0206], John Ogness wrote: > > Where does this "--latency=" option apply to? > > It is the value written to /dev/cpu_dma_latency, which AFAIK writes the > maximum acceptable latency (in microseconds). This translates to the > allowed C states. cyclictest currently writes 0, which should keep the > processor in C0. For example, setting it to 1-5, should allow C0 and C1. > > Using --laptop will cause cyclictest to avoid touching > /dev/cpu_dma_latency. But nobody would know that unless they looked at > the code. Exactly. We want to measure not to change the defaults before we start doing so. > IMHO, systems should be configured for production use and cyclictest > should just _measure_ latencies at a specified priority level. But by > default cyclictest is adjusting global system behavior during > measurements, thus providing results that the system (as it is actually > configured) would not be able to provide. > > I realize that nobody wants to touch defaults. But I'm not sure users > are aware how important the --laptop option is for realistic > measurements. In fact, the description of --laptop even encourages users > _not_ to use it. :-/ We don't want to touch the defaults? Not so long ago I was curious why the -b argument didn't stop the trace. Apparently I didn't use the --tracemark option which is required nowadays. > John Ogness Sebastian