From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756440Ab0IHJvo (ORCPT ); Wed, 8 Sep 2010 05:51:44 -0400 Received: from www.tglx.de ([62.245.132.106]:55529 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751147Ab0IHJvm (ORCPT ); Wed, 8 Sep 2010 05:51:42 -0400 Date: Wed, 8 Sep 2010 11:51:13 +0200 (CEST) From: Thomas Gleixner To: Joakim Tjernlund cc: Eric Dumazet , linux-kernel@vger.kernel.org Subject: Re: slow nanosleep? In-Reply-To: Message-ID: References: <1283932600.2880.1.camel@edumazet-laptop> <1283934289.2880.12.camel@edumazet-laptop> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="-1463795968-1394950388-1283939474=:2477" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---1463795968-1394950388-1283939474=:2477 Content-Type: TEXT/PLAIN; charset=ISO-8859-15 Content-Transfer-Encoding: 8BIT On Wed, 8 Sep 2010, Joakim Tjernlund wrote: > Eric Dumazet wrote on 2010/09/08 10:24:49: > > > > Le mercredi 08 septembre 2010 à 10:04 +0200, Joakim Tjernlund a écrit : > > > > > That makes litte difference: > > > root@localhost ~ # ./nanosleep > > > nanosleep > > > req:0 :0 > > > tv_res:0 :112 > > > > > > > Here, result is 30 (with prctl()) > > instead of 95 (without) > > On x86 I notice a difference: > 7 vs 57. > however select is still faster: 2 > The system call OH seems to be bigger for nanosleep than > for select and on my ppc is is about 112 us. Can anything > be done about that? Hmm, the only reason I can see is that select calls finally schedule_hrtimeout_range_clock() which optimizes the expiry = 0 case while nanosleep does not. So the difference is only visiable when the relative timeout is 0. For timeouts > 0 nanosleep and select should behave the same way. Thanks, tglx --- kernel/hrtimer.c | 3 +++ 1 file changed, 3 insertions(+) Index: linux-2.6/kernel/hrtimer.c =================================================================== --- linux-2.6.orig/kernel/hrtimer.c +++ linux-2.6/kernel/hrtimer.c @@ -1609,6 +1609,9 @@ SYSCALL_DEFINE2(nanosleep, struct timesp if (!timespec_valid(&tu)) return -EINVAL; + if (!tu.tv_sec && !tu.tv_usec) + return 0; + return hrtimer_nanosleep(&tu, rmtp, HRTIMER_MODE_REL, CLOCK_MONOTONIC); } ---1463795968-1394950388-1283939474=:2477--