Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932600AbVLMSfX (ORCPT ); Tue, 13 Dec 2005 13:35:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932601AbVLMSfX (ORCPT ); Tue, 13 Dec 2005 13:35:23 -0500 Received: from omx2-ext.sgi.com ([192.48.171.19]:53888 "EHLO omx2.sgi.com") by vger.kernel.org with ESMTP id S932600AbVLMSfW (ORCPT ); Tue, 13 Dec 2005 13:35:22 -0500 Message-ID: <439F1455.7080402@engr.sgi.com> Date: Tue, 13 Dec 2005 10:35:01 -0800 From: Jay Lan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040906 X-Accept-Language: en-us, en MIME-Version: 1.0 To: john stultz Cc: Shailabh Nagar , 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> In-Reply-To: <1134416962.14627.7.camel@cog.beaverton.ibm.com> X-Enigmail-Version: 0.86.0.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1505 Lines: 52 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 > > 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/