From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nivedita Singhvi Subject: Re: Query regarding 2.6.335 RT and Non-RT performance Date: Tue, 17 Aug 2010 12:45:27 -0700 Message-ID: <4C6AE6D7.2060006@us.ibm.com> References: <4C6AC4A6.4080407@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: David Sommerseth , linux-rt-users@vger.kernel.org To: Manikandan Ramachandran Return-path: Received: from e33.co.us.ibm.com ([32.97.110.151]:55052 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752074Ab0HQTog (ORCPT ); Tue, 17 Aug 2010 15:44:36 -0400 Received: from d03relay03.boulder.ibm.com (d03relay03.boulder.ibm.com [9.17.195.228]) by e33.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id o7HJdjTH008328 for ; Tue, 17 Aug 2010 13:39:45 -0600 Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o7HJiRDw176892 for ; Tue, 17 Aug 2010 13:44:28 -0600 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o7HJlron011702 for ; Tue, 17 Aug 2010 13:47:53 -0600 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 08/17/2010 11:24 AM, Manikandan Ramachandran wrote: > Thanks David& Mark for your valuable input! > > I'm not expecting RT kernel to be real fast. However I expect latency > of higher priority task to be less in RT kernel. I'll run the tests > that you have suggested and see if there is any inherent issue with my > system. Actually, a more accurate statement would be "I expect max latency of higher priority task to be less in RT kernel." This is true for max latency as reported by you (max, min): Stock: 418011us 3s RT: 366156us 3s So while the min might reflect the best that the system can do, the max does seem a tad high -- you do need to look into that. > One more query, with RT patch is it possible for higher priority task > to preempt a lower priority IRQ thread [For eg, IDE] ? If so when does > that happen, during next timer interrupt [Assuming IRQ thread uses > whole schedule slot and doesn't yield between]? Yes, and when that higher priority task becomes runnable. thanks, Nivedita