From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joachim Achtzehnter Subject: Re: Using patch-2.6.33.7.2-rt30 increases latency and CPU usage? Date: Wed, 09 May 2012 15:13:07 -0700 Message-ID: <4FAAEBF3.10907@netacquire.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-rt-users@vger.kernel.org To: unlisted-recipients:; (no To-header on input) Return-path: Received: from penguin.kraut.ca ([209.53.201.119]:48749 "EHLO penguin.kraut.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756028Ab2EIWzE (ORCPT ); Wed, 9 May 2012 18:55:04 -0400 Received: from s216-232-14-254.bc.hsia.telus.net ([216.232.14.254] helo=[205.159.216.152]) by penguin.kraut.ca with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.77) (envelope-from ) id 1SSF8D-0006hZ-FG for linux-rt-users@vger.kernel.org; Wed, 09 May 2012 15:13:14 -0700 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: Grant Edwards wrote: > I've been loaned a clue by somebody on the OSADL mailing list: the RT > patches are for improving _user_space_ reponse, and may do so at the > expense of both CPU usage and interrupt latency. The RT patches improve *worst case* latency. They are primarily intended for applications that must *always* meet their deadlines, not merely most of the time. In return you tend to get increased average latency as well as reduced throughput. > As a result, I'm better off without the RT patch if what I care > about is interrupt latency. Yes, if you only care about *typical* interrupt latency but don't mind the occasional long delay. Joachim -- joachima@netacquire.com http://www.netacquire.com