From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267366AbUHPCvf (ORCPT ); Sun, 15 Aug 2004 22:51:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267364AbUHPCvf (ORCPT ); Sun, 15 Aug 2004 22:51:35 -0400 Received: from mx2.elte.hu ([157.181.151.9]:21738 "EHLO mx2.elte.hu") by vger.kernel.org with ESMTP id S267366AbUHPCuZ (ORCPT ); Sun, 15 Aug 2004 22:50:25 -0400 Date: Mon, 16 Aug 2004 04:50:51 +0200 From: Ingo Molnar To: Lee Revell Cc: Florian Schmidt , linux-kernel , Felipe Alfaro Solana Subject: Re: [patch] voluntary-preempt-2.6.8.1-P0 Message-ID: <20040816025051.GA9481@elte.hu> References: <20040812235116.GA27838@elte.hu> <1092382825.3450.19.camel@mindpipe> <20040813104817.GI8135@elte.hu> <1092432929.3450.78.camel@mindpipe> <20040814072009.GA6535@elte.hu> <20040815115649.GA26259@elte.hu> <20040816022554.16c3c84a@mango.fruits.de> <1092622121.867.109.camel@krustophenia.net> <20040816023655.GA8746@elte.hu> <1092624221.867.118.camel@krustophenia.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1092624221.867.118.camel@krustophenia.net> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Lee Revell wrote: > I believe the constant-time behavior that I reported was an artifact > of ALSA xrun debugging. Now it seems like the latency produced *does* > correspond directly to the amount of memory being mlockall'ed. If > ./mlockall-test 1500 triggers an xrun at all it's ~0.2ms. 3000 > triggers a ~1ms xrun, and 10000 a ~3 ms xrun. ah ... could this be some DMA starvation effect? Or is this xrun calculated from arrival of the audio interrupt (hence DMA completion) to the actual running of jackd? > > could you try another thing: modify mlockall-test.cc to use mlock() on > > the freshly allocated anonymous pages? Does this produce the same > > latencies? mlockall() prefaults _all_ pages the process currently has. > > Maybe mlockall() touches some page that is mapped both by jackd and > > mlockall-test and thus somehow interacts with jackd's scheduling. > > I don't know C++, Florian wrote this program. Can you provide a > pseudo-patch? your above observation wrt. linearity of the xrun makes it less likely that the issue is caused by page sharing between jackd and mlockall-test. (if then they share a constant amount of pages.) but it would be nice to test it anyway, i've attached mlock-test.cc. Ingo