Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755386AbZD2JMo (ORCPT ); Wed, 29 Apr 2009 05:12:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752420AbZD2JMb (ORCPT ); Wed, 29 Apr 2009 05:12:31 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:35457 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751873AbZD2JMa (ORCPT ); Wed, 29 Apr 2009 05:12:30 -0400 Date: Wed, 29 Apr 2009 11:11:30 +0200 From: Ingo Molnar To: Eric Dumazet Cc: Christoph Lameter , linux kernel , Andi Kleen , David Miller , jesse.brandeburg@intel.com, netdev@vger.kernel.org, haoki@redhat.com, mchan@broadcom.com, davidel@xmailserver.org Subject: Re: [PATCH] poll: Avoid extra wakeups in select/poll Message-ID: <20090429091130.GA27857@elte.hu> References: <49F43B8F.2050907@cosmosbay.com> <87ab60rh8t.fsf@basil.nowhere.org> <49F71B63.8010503@cosmosbay.com> <49F76174.6060009@cosmosbay.com> <49F767FD.2040205@cosmosbay.com> <49F76F6C.80005@cosmosbay.com> <49F77108.7060509@cosmosbay.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49F77108.7060509@cosmosbay.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1511 Lines: 40 * Eric Dumazet wrote: > On uddpping, I had prior to the patch about 49000 wakeups per > second, and after patch about 26000 wakeups per second (matches > number of incoming udp messages per second) very nice. It might not show up as a real performance difference if the CPUs are not fully saturated during the test - but it could show up as a decrease in CPU utilization. Also, if you run the test via 'perf stat -a ./test.sh' you should see a reduction in instructions executed: aldebaran:~/linux/linux> perf stat -a sleep 1 Performance counter stats for 'sleep': 16128.045994 task clock ticks (msecs) 12876 context switches (events) 219 CPU migrations (events) 186144 pagefaults (events) 20911802763 CPU cycles (events) 19309416815 instructions (events) 199608554 cache references (events) 19990754 cache misses (events) Wall-clock time elapsed: 1008.882282 msecs With -a it's measured system-wide, from start of test to end of test - the results will be a lot more stable (and relevant) statistically than wall-clock time or CPU usage measurements. (both of which are rather imprecise in general) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/