From mboxrd@z Thu Jan 1 00:00:00 1970 From: Clark Williams Subject: Re: [PATCH RFC] rdtscbench: a nohz_full validation and benchmarking tool Date: Fri, 11 Dec 2015 14:40:27 -0600 Message-ID: <20151211144027.099b2fa0@sluggy.hsv.redhat.com> References: <1440189958-6959-1-git-send-email-isaac.griswoldsteiner@ni.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: jkacur@redhat.com, linux-rt-users@vger.kernel.org, joshc@ni.com, Isaac Griswold-Steiner To: Isaac Griswold-Steiner Return-path: Received: from mx1.redhat.com ([209.132.183.28]:43386 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751039AbbLKUk3 (ORCPT ); Fri, 11 Dec 2015 15:40:29 -0500 In-Reply-To: <1440189958-6959-1-git-send-email-isaac.griswoldsteiner@ni.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Fri, 21 Aug 2015 15:45:58 -0500 Isaac Griswold-Steiner wrote: > From: Isaac Griswold-Steiner > > rdtscbench is a cyclictest-like tool that spawns a thread per cpu. Each thread > measures the difference in cycle count (using the tsc) during the execution of a > tight loop. > > This is a simple tool intended to be used for the validation of nohz_full CPU > configurations. As the validation of nohz_full CPUs is the objective, the tool > avoids the usage of system calls, timers, or anything that might break nohz_full. > Isaac, A question and a request. Was there any particular reason you used sleep() rather than clock_nanosleep() in your cycles_per_second function? I see that you did ten samples but wondered if the slop from a HZ-based wakeup might still introduce some error, as opposed to a more precise programmed wakeup. Also, I'd appreciate it if you would expand a bit on the usage section in your README file, specifically how you tune a system prior to running rdtscbench, what output indicates that your tuning is *not* working, versus when to know you're doing the right things. It's probably as simple as saying "if the max latency numbers are spiking you have a problem" but it's good to be explicit about that sort of thing. Thanks, Clark