Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757634AbYFYMUg (ORCPT ); Wed, 25 Jun 2008 08:20:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755899AbYFYMU2 (ORCPT ); Wed, 25 Jun 2008 08:20:28 -0400 Received: from rv-out-0506.google.com ([209.85.198.238]:7765 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755810AbYFYMU1 (ORCPT ); Wed, 25 Jun 2008 08:20:27 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=S/tuWyYIPd94UhBBR+Cq3LFCwtTpGzwH8oOpsKg57goZlG4GuebB4FZ9ZkEDwbrOmO Of7gBsWjBzcNHw1MQ22jrbVEUUsviPsyroY8RbnKMdz5DMKWHDfDOq+xjw9VKjd3FKGX FvOsFEXuZzihrKP2TH8tZTI95wT/vzp3g/g04= Message-ID: Date: Wed, 25 Jun 2008 14:20:26 +0200 From: "Michael Kerrisk" To: "Thomas Gleixner" Subject: Re: When did High-Resolution Timers hit mainline? Cc: "Ingo Molnar" , lkml , "Roman Zippel" , "john stultz" , "Bart Van Assche" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2010 Lines: 50 Thomas, On Wed, Jun 25, 2008 at 9:09 AM, Thomas Gleixner wrote: > On Wed, 25 Jun 2008, Michael Kerrisk wrote: >> High-Resolution Timers >> Before Linux 2.6.16, the accuracy of timer and sleep system >> calls (see below) was also limited by the size of the jiffy. >> >> Since Linux 2.6.16, Linux supports high-resolution timers >> (HRTs), optionally configurable since kernel 2.6.21 via CON- >> FIG_HIGH_RES_TIMERS. On a system that supports HRTs, the accu- >> racy of sleep and timer system calls is no longer constrained >> by the jiffy, but instead can be as accurate as the hardware >> allows (microsecond accuracy is typical of modern hardware). > > Hmm, that's a bit backwards. We changed the internal handling of those > interfaces to hrtimers in 2.6.16, but the accuracy is still jiffies > unless you have CONFIG_HIGH_RES_TIMERS enabled (which is only possible > as of 2.6.21) and your system provides the necessary hardware. So then it's simply enough to say: Since Linux 2.6.17, Linux optionaly supports high-resolution timers (configurable via CONFIG_HIGH_RES_TIMERS). right? >> HRTs are not supported on all hardware architectures. (Support >> is provided on x86, arm, and powerpc, among others.) > > Also you might point out that you can check whether high resolution > timers are active via clock_getres() or by checking the resolution > entry in /proc/timer_list. Okay -- thanks. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- 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/