From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756868AbZEZUar (ORCPT ); Tue, 26 May 2009 16:30:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754439AbZEZUak (ORCPT ); Tue, 26 May 2009 16:30:40 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:36880 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754058AbZEZUaj (ORCPT ); Tue, 26 May 2009 16:30:39 -0400 Subject: Re: [PATCH] sched: Support current clocksource handling in fallback sched_clock(). From: Peter Zijlstra To: john stultz Cc: Linus Walleij , Paul Mundt , Ingo Molnar , Andrew Victor , Haavard Skinnemoen , Andrew Morton , linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, linux-arm-kernel@lists.arm.linux.org.uk, John Stultz , Thomas Gleixner In-Reply-To: <1243369423.3275.5.camel@localhost> References: <20090526061532.GD9188@linux-sh.org> <63386a3d0905260731m655bfee3q82a6f52d71fa3cef@mail.gmail.com> <1243348681.23657.14.camel@twins> <1243369423.3275.5.camel@localhost> Content-Type: text/plain Date: Tue, 26 May 2009 22:30:15 +0200 Message-Id: <1243369815.6600.2.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-05-26 at 13:23 -0700, john stultz wrote: > Overall, I'd probably suggest thinking this through a bit more. At some > point doing this right will cause sched_clock() to be basically the same > as ktime_get(). So why not just use that instead of remaking it? simply because we don't require the strict global monotonicy for scheduling as we do from a regular time source (its nice to have though). That means that on x86 we can always use TSC for sched_clock(), even when its quite unsuitable for ktime.