Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755121AbYCQRER (ORCPT ); Mon, 17 Mar 2008 13:04:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752524AbYCQREF (ORCPT ); Mon, 17 Mar 2008 13:04:05 -0400 Received: from saraswathi.solana.com ([198.99.130.12]:40638 "EHLO saraswathi.solana.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751956AbYCQRED (ORCPT ); Mon, 17 Mar 2008 13:04:03 -0400 Date: Mon, 17 Mar 2008 13:03:28 -0400 From: Jeff Dike To: Nix Cc: clowncoder , user-mode-linux-devel@lists.sourceforge.net, linux-kernel Mailing List , Thomas Gleixner Subject: Re: [2.6.24.x] UML select()/poll() oversleeping reproducibly (was Re: [uml-devel] g_timeout_add) Message-ID: <20080317170328.GB9536@c2.user-mode-linux.org> References: <47B34BA0.30006@club-internet.fr> <20080214003853.GA15952@c2.user-mode-linux.org> <47B4BDCD.4080605@club-internet.fr> <20080215160205.GA6082@c2.user-mode-linux.org> <47B5CE40.9000005@club-internet.fr> <20080215184650.GA8810@c2.user-mode-linux.org> <87y78kx640.fsf_-_@hades.wkstn.nix> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87y78kx640.fsf_-_@hades.wkstn.nix> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1940 Lines: 52 On Fri, Mar 14, 2008 at 11:01:35PM +0000, Nix wrote: > bash-3.2# ./select-sleep 10 > Slept for 13 seconds. See what kind of difference the patch below makes - it reduces the 30% oversleeping down to 10% for me. That's still way too much, but it's better. The problem being fixed here is that setitimer consistently returns a remaining time greater than what was originally requested, by ~20%: 1205773032.413780 setitimer(ITIMER_VIRTUAL, {it_interval={0, 10000}, it_value={0, 10000}}, NULL) = 0 1205773032.413814 setitimer(ITIMER_VIRTUAL, {it_interval={0, 0}, it_value={0, 0}}, {it_interval={0, 10998}, it_value={0, 11998}}) = 0 This is setting a 100 HZ timer, immediately followed by a cancellation which also requests the amount left on the timer. The interval is rounded up by 10%, and the first tick by 20%. Jeff -- Work email - jdike at linux dot intel dot com Index: linux-2.6.22/arch/um/os-Linux/time.c =================================================================== --- linux-2.6.22.orig/arch/um/os-Linux/time.c 2008-02-18 11:53:51.000000000 -0500 +++ linux-2.6.22/arch/um/os-Linux/time.c 2008-03-17 12:55:41.000000000 -0400 @@ -58,12 +58,17 @@ static inline long long timeval_to_ns(co long long disable_timer(void) { struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } }); + int remain, max = UM_NSEC_PER_SEC / UM_HZ; if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0) printk(UM_KERN_ERR "disable_timer - setitimer failed, " "errno = %d\n", errno); - return timeval_to_ns(&time.it_value); + remain = timeval_to_ns(&time.it_value); + if (remain > max) + remain = max; + + return remain; } long long os_nsecs(void) -- 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/