Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754773AbYFYHSE (ORCPT ); Wed, 25 Jun 2008 03:18:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752115AbYFYHRy (ORCPT ); Wed, 25 Jun 2008 03:17:54 -0400 Received: from www.tglx.de ([62.245.132.106]:34599 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751859AbYFYHRy (ORCPT ); Wed, 25 Jun 2008 03:17:54 -0400 Date: Wed, 25 Jun 2008 09:09:39 +0200 (CEST) From: Thomas Gleixner To: Michael Kerrisk cc: Ingo Molnar , lkml , Roman Zippel , john stultz Subject: Re: When did High-Resolution Timers hit mainline? In-Reply-To: Message-ID: References: User-Agent: Alpine 1.10 (LFD 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1489 Lines: 33 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. > 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. Thanks, tglx -- 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/