Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932154AbVLLUHW (ORCPT ); Mon, 12 Dec 2005 15:07:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932163AbVLLUHW (ORCPT ); Mon, 12 Dec 2005 15:07:22 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:63661 "EHLO e36.co.us.ibm.com") by vger.kernel.org with ESMTP id S932154AbVLLUHV (ORCPT ); Mon, 12 Dec 2005 15:07:21 -0500 Subject: Re: [Lse-tech] [RFC][Patch 1/5] nanosecond timestamps and diffs From: john stultz To: Shailabh Nagar Cc: Christoph Lameter , linux-kernel , elsa-devel , lse-tech@lists.sourceforge.net, ckrm-tech , Guillaume Thouvenin , Jay Lan , Jens Axboe In-Reply-To: <439DD6E8.7010802@watson.ibm.com> References: <43975D45.3080801@watson.ibm.com> <43975E6D.9000301@watson.ibm.com> <439DD01A.2060803@watson.ibm.com> <1134416962.14627.7.camel@cog.beaverton.ibm.com> <439DD6E8.7010802@watson.ibm.com> Content-Type: text/plain Date: Mon, 12 Dec 2005 12:07:14 -0800 Message-Id: <1134418034.14627.14.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2058 Lines: 50 On Mon, 2005-12-12 at 20:00 +0000, Shailabh Nagar wrote: > john stultz wrote: > > On Mon, 2005-12-12 at 19:31 +0000, Shailabh Nagar wrote: > > > >>Christoph Lameter wrote: > >> > >>>On Wed, 7 Dec 2005, Shailabh Nagar wrote: > >>>>+void getnstimestamp(struct timespec *ts) > >>> > >>>There is already getnstimeofday in the kernel. > >> > >>Yes, and that function is being used within the getnstimestamp() being proposed. > >>However, John Stultz had advised that getnstimeofday could get affected by calls to > >>settimeofday and had recommended adjusting the getnstimeofday value with wall_to_monotonic. > >> > >>John, could you elaborate ? > > > > I think you pretty well have it covered. > > > > getnstimeofday + wall_to_monotonic should be higher-res and more > > reliable (then TSC based sched_clock(), for example) for getting a > > timestamp. > > > > There may be performance concerns as you have to access the clock > > hardware in getnstimeofday(), but there really is no other way for > > reliable finely grained monotonically increasing timestamps. > > > Thanks, that clarifies. I guess the other underlying concern here would be whether these > improvements (in resolution and reliability) should be going into getnstimeofday() > itself (rather than creating a new func for the same) ? Or is it better to leave > getnstimeofday as it is ? No, getnstimeofday() is very much needed to get a nanosecond grained wall-time clock, so a new function is needed for the monotonic clock. In my timeofday re-work I have used the name "get_monotonic_clock()" and "get_monotonic_clock_ts()" for basically the same functionality (providing a ktime and a timespec respectively). You might consider naming it as such, but resolving these naming collisions shouldn't be too difficult either way. thanks -john - 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/