From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 22 Sep 2001 23:19:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 22 Sep 2001 23:19:39 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:22510 "EHLO hermes.mvista.com") by vger.kernel.org with ESMTP id ; Sat, 22 Sep 2001 23:19:24 -0400 Message-ID: <3BAD5493.EC4F845A@mvista.com> Date: Sat, 22 Sep 2001 20:18:43 -0700 From: george anzinger Organization: Monta Vista Software X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.2.12-20b i686) X-Accept-Language: en MIME-Version: 1.0 To: Andre Pang CC: Robert Love , linux-kernel@vger.kernel.org, safemode@speakeasy.net, Dieter.Nuetzel@hamburg.de, iafilius@xs4all.nl, ilsensine@inwind.it Subject: Re: [PATCH] Preemption Latency Measurement Tool In-Reply-To: <1000939458.3853.17.camel@phantasy> <1001131036.557760.4340.nullmailer@bozar.algorithm.com.au> <1001139027.1245.28.camel@phantasy> <1001143341.117502.5311.nullmailer@bozar.algorithm.com.au> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andre Pang wrote: > > On Sat, Sep 22, 2001 at 02:10:18AM -0400, Robert Love wrote: > > > > i did a test of it on linux-2.4.10-pre13 with Benno Senoner's > > > lowlatency program, which i hacked up a bit to output > > > /proc/latencytimes after each of the graphs. test results are at > > > > > > http://www.algorithm.com.au/hacking/linux-lowlatency/2.4.10-pre13-pes/ > > > > > > and since i stared at the results in disbelief, i won't even try > > > to guess what's going on :). maybe you can make some sense of > > > it? > > > > Well, its not hard to decipher...and really, its actually fairly good. > > the latency test program is giving you a max latency of around 12ms in > > each test, which is OK. > > arrgh! i just realised my script buggered up and was producing the same > graph for all the results. please have a look at the page again, sorry. > > apart from that, i'm still confused. compared to other graphs produced > by the latencytest program, my system seems to have huge latencies. > unless i'm reading it wrongly, the graph is saying that i'm getting > latencies of up to 30ms, and a lot of overruns. compare this to > > http://www.gardena.net/benno/linux/audio/2.4.0-test2/3x256.html > > which shows latencytest on 2.4.0-test2, and > > http://www.gardena.net/benno/linux/audio/2.2.10-p133-3x128/3x128.html > > which are the results for latencytest on 2.2.10. admittedly these > kernels are much older, but i'm consistently getting far more latency > than those kernels. that's the bit i'm confused about :) i've tried > Andrew Morton's low-latency patches as well, to no avail. i've made > sure i've tuned my hard disks correctly, and i don't have any other > realtime processes running. > > am i concerned with a different issue than the one you're addressing? > > > the preemption-test patch is showing _MAX_ latencies of 0.8ms through > > 12ms. this is fine, too. > > yep, i agree with that ... so why is latencytest showing scheduling > latencies of > 30ms? i get the feeling i'm confusing two different > issues here. from what i understand, /proc/latencytimes shows the > how long it takes for various functions in the kernel to finish, and > the latencytest result shows how long it takes for it to be > re-scheduled (represented by the white line on the graph). The one thing the latancytimes patch doesn't monitor is interrupt off time. Maybe it should... George