From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266204AbUHNI53 (ORCPT ); Sat, 14 Aug 2004 04:57:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266254AbUHNI5Z (ORCPT ); Sat, 14 Aug 2004 04:57:25 -0400 Received: from mx1.elte.hu ([157.181.1.137]:19850 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S266204AbUHNIzx (ORCPT ); Sat, 14 Aug 2004 04:55:53 -0400 Date: Sat, 14 Aug 2004 10:57:31 +0200 From: Ingo Molnar To: Florian Schmidt Cc: linux-kernel@vger.kernel.org, Lee Revell , Felipe Alfaro Solana , Andrew Morton Subject: Re: [patch] Latency Tracer, voluntary-preempt-2.6.8-rc4-O6 Message-ID: <20040814085731.GA7033@elte.hu> References: <20040729222657.GA10449@elte.hu> <20040801193043.GA20277@elte.hu> <20040809104649.GA13299@elte.hu> <20040810132654.GA28915@elte.hu> <20040812235116.GA27838@elte.hu> <20040813124249.13066d94@mango.fruits.de> <20040813105406.GJ8135@elte.hu> <20040813140321.78da570d@mango.fruits.de> <20040813120302.GA18221@elte.hu> <20040813145510.60e9e0f3@mango.fruits.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040813145510.60e9e0f3@mango.fruits.de> 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 * Florian Schmidt wrote: > This is something i wanted to ask anyways: In one of your first VP > announcements you mentioned you wanted to eliminate all latencies > 1 > ms. To me it seems, that that goal is pretty much reached [at least i > don't see any longer ones except for at boot and shutdown]. So the > question is: What is the lower limit for laterncies that you want to > hear reports about? well ... i'm interested in all latencies that are well above the typical average latencies in the system. E.g. when the average is around 20-30 usecs then reports of 200-300 usecs would be interesting. there's no hard limit, really. Also, sometimes latencies that are 0.3 msec in the report could be 3 msec if triggered properly. So a seemingly lower than 1 msec latency can very well pinpoint a problem area. > WRT mlockall: i tried mlockall'ing 500 megs. This produced a new max > latency of 299 us. the trace is rather long. This one is with jackd > running and the one below this is w/o jackd running: > 0.010ms (+0.000ms): free_page_and_swap_cache (clear_page_tables) > 0.010ms (+0.000ms): __page_cache_release (clear_page_tables) > 0.010ms (+0.000ms): free_hot_page (clear_page_tables) hm, the reason for this one is that clear_page_tables() does all the freeing in a single uninterrupted critical section covered by mm->page_table_lock. This function needs a lock-break i believe. Especially in the process-exit case (exit_mmap()) the lock seems unjustified - the current task is the sole owner of a never-to-be-used-again collection of pagetables. Ingo