From: Vojtech Pavlik <vojtech@suse.cz>
To: Andi Kleen <ak@suse.de>
Cc: Christoph Lameter <clameter@sgi.com>,
Arjan van de Ven <arjan@infradead.org>,
Jiri Bohac <jbohac@suse.cz>,
linux-kernel@vger.kernel.org, ssouhlal@freebsd.org,
tglx@linutronix.de, johnstul@us.ibm.com, zippel@linux-m68k.org,
andrea@suse.de
Subject: Re: [patch 4/9] Remove the TSC synchronization on SMP machines
Date: Tue, 13 Feb 2007 23:18:48 +0100 [thread overview]
Message-ID: <20070213221848.GF9189@suse.cz> (raw)
In-Reply-To: <200702131820.15180.ak@suse.de>
On Tue, Feb 13, 2007 at 06:20:14PM +0100, Andi Kleen wrote:
> On Tuesday 13 February 2007 18:09, Christoph Lameter wrote:
> > On Tue, 13 Feb 2007, Arjan van de Ven wrote:
> >
> > > no quite the opposite. gettimeofday() currently is NOT monotonic
> > > unfortunately. With this patchseries it actually has a better chance of
> > > becoming that...
> >
> > It is monotonic on IA64 at least and we have found that subtle application
> > bugs occur if it is not. IA64 (and other arches using time interpolation)
> > can insure the monotoneity of time sources. Are you sure about this? I
> > wonder why the new time of day subsystem does not have that?
>
> Just to avoid spreading misinformation: modulo some new broken hardware
> (which we always try to work around when found) i386/x86-64 gettimeofday
> is monotonic. AFAIK on the currently known hardware it should be generally
> ok.
>
> However ntpd can always screw you up, but that's inherent in the design.
It's not inherent to ntpd's design, but the current (which may have been
fixed since I looked last) implementation of the NTP PLL in the kernel.
The interaction with ntpd can be fixed and I've done it in the past
once, although the fix wasn't all that nice.
> Safer in general is to use clock_gettime(CLOCK_MONOTONIC, ...) which
> guarantees no interference from ntpd
--
Vojtech Pavlik
Director SuSE Labs
next prev parent reply other threads:[~2007-02-13 22:18 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-01 9:59 [patch 0/9] x86_64: reliable TSC-based gettimeofday jbohac
2007-02-01 9:59 ` [patch 1/9] Fix HPET init race jbohac
2007-02-02 2:34 ` Andrew Morton
2007-02-06 16:44 ` Jiri Bohac
2007-02-07 0:12 ` Andrew Morton
2007-02-10 12:31 ` Andi Kleen
2007-07-26 20:58 ` Robin Holt
2007-02-01 9:59 ` [patch 2/9] Remove the support for the VXTIME_PMTMR timer mode jbohac
2007-02-01 11:13 ` Andi Kleen
2007-02-01 13:13 ` Jiri Bohac
2007-02-01 13:13 ` Andi Kleen
2007-02-01 13:59 ` Jiri Bohac
2007-02-01 14:18 ` Andi Kleen
2007-02-01 9:59 ` [patch 3/9] Remove the support for the VXTIME_HPET " jbohac
2007-02-01 9:59 ` [patch 4/9] Remove the TSC synchronization on SMP machines jbohac
2007-02-01 11:14 ` Andi Kleen
2007-02-01 13:17 ` Jiri Bohac
2007-02-01 15:16 ` Vojtech Pavlik
2007-02-02 7:14 ` Andi Kleen
2007-02-13 0:34 ` Christoph Lameter
2007-02-13 6:40 ` Arjan van de Ven
2007-02-13 8:28 ` Andi Kleen
2007-02-13 8:41 ` Arjan van de Ven
2007-02-13 17:09 ` Christoph Lameter
2007-02-13 17:20 ` Andi Kleen
2007-02-13 22:18 ` Vojtech Pavlik [this message]
2007-02-13 22:38 ` Andrea Arcangeli
2007-02-14 6:59 ` Vojtech Pavlik
2007-02-13 23:55 ` Christoph Lameter
2007-02-14 0:18 ` Paul Mackerras
2007-02-14 0:25 ` john stultz
2007-02-02 7:13 ` Andi Kleen
2007-02-01 21:05 ` mbligh
2007-02-03 1:16 ` H. Peter Anvin
2007-02-01 9:59 ` [patch 5/9] Add all the necessary structures to the vsyscall page jbohac
2007-02-01 11:17 ` Andi Kleen
2007-02-01 9:59 ` [patch 6/9] Add the "Master Timer" jbohac
2007-02-01 11:22 ` Andi Kleen
2007-02-01 13:29 ` Jiri Bohac
2007-02-01 9:59 ` [patch 7/9] Adapt the time initialization code jbohac
2007-02-01 11:26 ` Andi Kleen
2007-02-01 13:41 ` Jiri Bohac
2007-02-01 10:00 ` [patch 8/9] Add time_update_mt_guess() jbohac
2007-02-01 11:28 ` Andi Kleen
2007-02-01 13:54 ` Jiri Bohac
2007-02-01 10:00 ` [patch 9/9] Make use of the Master Timer jbohac
2007-02-01 11:36 ` Andi Kleen
2007-02-01 14:29 ` Jiri Bohac
2007-02-01 15:23 ` Vojtech Pavlik
2007-02-02 7:05 ` Andi Kleen
2007-02-02 7:04 ` Andi Kleen
2007-02-01 11:20 ` [patch 0/9] x86_64: reliable TSC-based gettimeofday Andi Kleen
2007-02-01 11:53 ` Andrea Arcangeli
2007-02-01 12:02 ` Andi Kleen
2007-02-01 12:54 ` Andrea Arcangeli
2007-02-01 12:17 ` Ingo Molnar
2007-02-01 14:52 ` Jiri Bohac
2007-02-01 16:56 ` john stultz
2007-02-01 19:41 ` Vojtech Pavlik
2007-02-01 11:34 ` Ingo Molnar
2007-02-01 11:46 ` [-mm patch] x86_64 GTOD: offer scalable vgettimeofday Ingo Molnar
2007-02-01 12:01 ` Andi Kleen
2007-02-01 12:14 ` Ingo Molnar
2007-02-01 12:17 ` [-mm patch] x86_64 GTOD: offer scalable vgettimeofday II Andi Kleen
2007-02-01 12:24 ` Ingo Molnar
2007-02-01 12:45 ` Andi Kleen
2007-02-02 4:22 ` [patch 0/9] x86_64: reliable TSC-based gettimeofday Andrew Morton
2007-02-02 7:07 ` Andi Kleen
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