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From: john stultz <johnstul@us.ibm.com>
To: Chris Friesen <cfriesen@nortel.com>
Cc: Lee Revell <rlrevell@joe-job.com>,
	Roman Zippel <zippel@linux-m68k.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@osdl.org>,
	George Anzinger <george@mvista.com>,
	Ulrich Windl <ulrich.windl@rz.uni-regensburg.de>
Subject: Re: [PATCH 1/6] new timeofday core subsystem for -mm (v.B3)
Date: Tue, 21 Jun 2005 10:20:37 -0700	[thread overview]
Message-ID: <1119374438.9947.151.camel@cog.beaverton.ibm.com> (raw)
In-Reply-To: <42B82A4F.5090804@nortel.com>

On Tue, 2005-06-21 at 08:55 -0600, Chris Friesen wrote:
> Lee Revell wrote:
> 
> > But some user space apps are now *required* to use rdtsc for timing due
> > to the massive performance difference.  If we only took a 5x or 10x
> > performance hit vs rdtsc, rather than the current 50x, it might be
> > enough that user space apps won't have to do this.
> 
> For my userspace apps I've actually switched to 
> clock_gettime(CLOCK_MONOTONIC, &ts);
> 
> This at least guarantees that it will never go backwards.
> 
> For the experts: Is there a clock exported to userspace that is both 
> monotonic and uniform?  Does CLOCK_MONOTONIC give this on linux?

clock_gettime(CLOCK_MONOTONIC) should be what you're looking for. Since
that still uses do_gettimeofday internally, it is still possible in some
conditions for the current code to have time inconsistencies caused by
interpolation error. This is one of the major reasons for my work.

thanks
-john


  reply	other threads:[~2005-06-21 17:23 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-06-18  2:56 john stultz
2005-06-18  2:58 ` [PATCH 2/6] new timeofday i386 arch specific changes, part 1 " john stultz
2005-06-18  2:59   ` [PATCH 3/6] new timeofday i386 arch specific changes, part 2 " john stultz
2005-06-18  3:01     ` [PATCH 4/6] new timeofday i386 arch specific changes, part 3 " john stultz
2005-06-18  3:02       ` [PATCH 5/6] new timeofday i386 arch specific changes, part 4 " john stultz
2005-06-18  3:04         ` [PATCH 6/6] new timeofday i386 specific timesources " john stultz
2005-06-18 12:02 ` [PATCH 1/6] new timeofday core subsystem " Roman Zippel
2005-06-20  7:01   ` Ulrich Windl
2005-06-20 10:22     ` Roman Zippel
2005-06-20 10:31       ` Ulrich Windl
2005-06-20 10:54         ` Roman Zippel
2005-06-20 11:04         ` Christoph Hellwig
2005-06-20 17:09   ` john stultz
2005-06-20 18:10     ` Lee Revell
2005-06-20 21:53       ` john stultz
2005-06-20 23:44         ` Lee Revell
2005-06-21 14:55           ` Chris Friesen
2005-06-21 17:20             ` john stultz [this message]
2005-06-21  6:26       ` Ulrich Windl
2005-06-20 22:05     ` Roman Zippel
2005-06-20 23:40       ` Lee Revell
2005-06-20 23:55       ` john stultz
2005-06-21 15:08         ` Roman Zippel
2005-06-22  0:57           ` john stultz
2005-06-22  2:39             ` john stultz
2005-06-22 19:45             ` Roman Zippel
2005-06-23  0:29               ` john stultz
2005-06-23 21:59                 ` Roman Zippel
2005-06-24  0:33                   ` john stultz
2005-06-24 10:58                     ` Roman Zippel
2005-06-21  6:42       ` Ulrich Windl
2005-06-21 15:13         ` Roman Zippel

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