Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967334AbWKZIYu (ORCPT ); Sun, 26 Nov 2006 03:24:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S967336AbWKZIYu (ORCPT ); Sun, 26 Nov 2006 03:24:50 -0500 Received: from pentafluge.infradead.org ([213.146.154.40]:36230 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S967334AbWKZIYu (ORCPT ); Sun, 26 Nov 2006 03:24:50 -0500 Subject: Re: [patch] x86: unify/rewrite SMP TSC sync code From: Arjan van de Ven To: Wink Saville Cc: Robert Hancock , linux-kernel In-Reply-To: <45694D6F.60100@saville.com> References: <4569404E.20402@shaw.ca> <45694D6F.60100@saville.com> Content-Type: text/plain Organization: Intel International BV Date: Sun, 26 Nov 2006 09:24:44 +0100 Message-Id: <1164529484.3147.68.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1.1 (2.8.1.1-3.fc6) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1212 Lines: 26 On Sun, 2006-11-26 at 00:16 -0800, Wink Saville wrote: > Robert Hancock wrote: > >>>> Actually, we need to ask the CPU/System makers to provide a system wide > > Generally user mode code should just be using gettimeofday. When the TSC > > is usable as a sane time source, the kernel will use it. When it's not, > > it will use something else like the HPET, ACPI PM Timer or (at last > > resort) the PIT, in increasing degrees of slowness. > > > > But gettimeofday is much too expensive compared to RDTSC. it's the cost of a syscall (1000 cycles?) plus what it takes to get a reasonable time estimate. Assuming your kernel has enough time support AND your tsc is reasonably ok, it'll be using that. If it's NOT using that then that's a pretty good sign that you can't also use it in userspace.... -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org - 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/