Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932506AbVLMVo7 (ORCPT ); Tue, 13 Dec 2005 16:44:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932608AbVLMVo7 (ORCPT ); Tue, 13 Dec 2005 16:44:59 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:59060 "EHLO e32.co.us.ibm.com") by vger.kernel.org with ESMTP id S932506AbVLMVo6 (ORCPT ); Tue, 13 Dec 2005 16:44:58 -0500 Message-ID: <439F40CF.3010908@watson.ibm.com> Date: Tue, 13 Dec 2005 21:44:47 +0000 From: Shailabh Nagar User-Agent: Debian Thunderbird 1.0.2 (X11/20051002) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jay Lan CC: john stultz , Christoph Lameter , linux-kernel , elsa-devel , lse-tech@lists.sourceforge.net, ckrm-tech , Guillaume Thouvenin , Jay Lan , Jens Axboe Subject: Re: [Lse-tech] [RFC][Patch 1/5] nanosecond timestamps and diffs References: <43975D45.3080801@watson.ibm.com> <43975E6D.9000301@watson.ibm.com> <439DD01A.2060803@watson.ibm.com> <1134416962.14627.7.camel@cog.beaverton.ibm.com> <439F1455.7080402@engr.sgi.com> In-Reply-To: <439F1455.7080402@engr.sgi.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1877 Lines: 77 Jay Lan 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. > > > How is this proposed function different from > do_posix_clock_monotonic_gettime()? > It calls getnstimeofday(), it also adjusts with wall_to_monotinic. > > It seems to me we just need to EXPORT_SYMBOL_GPL the > do_posix_clock_monotonic_gettime()? > > Thanks, > - jay > Hmmm. Looks like do_posix_clock_monotonic_gettime will suffice for this patch. Wonder why the clock parameter to do_posix_clock_monotonic_get is needed ? Doesn't seem to be used. Any possibility of these set of functions changing their behaviour ? -- Shailabh >> >> 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 >> -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/