From: Andi Kleen <ak@suse.de>
To: "Vladimir B. Savkin" <master@sectorb.msk.ru>
Cc: john stultz <johnstul@us.ibm.com>,
lkml <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@osdl.org>,
discuss@x86-64.org
Subject: Re: [PATCH] x86-64: Fix bad assumption that dualcore cpus have synced TSCs
Date: 11 Oct 2005 10:06:33 +0200 [thread overview]
Message-ID: <p73ll10v5o6.fsf@verdi.suse.de> (raw)
In-Reply-To: <20051011073532.GA29254@tentacle.sectorb.msk.ru>
"Vladimir B. Savkin" <master@sectorb.msk.ru> writes:
> On Mon, Oct 10, 2005 at 08:19:42PM +0200, Jonas Oreland wrote:
> > Hi,
> >
> > check http://bugzilla.kernel.org/show_bug.cgi?id=5283
>
> Excuse me for possibly dumb question, but is it safe to leave TSCs
> unsynchronized when using other time source?
> How will other subsystems e.g. traffic queueing disciplines react?
They might see hickups, but normally they all have relatively
benign failure modes so I wouldn't worry too much.
If you use it on a Opteron with frequency scaling and multiple sockets
it would be safer to patch them to use do_gettimeofday() or better
monotonic_clock(), because the differences can be very large there
(CPUs running with completely different frequencies). Drawback would
be that it would be slower. On systems without frequency scaling
you would likely only see problems if at all after a long uptime.
For some subsystems it is ok, e.g. the scheduler which also uses
TSCs especially deals with unsynchronized clocks.
-Andi
next prev parent reply other threads:[~2005-10-11 8:06 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-19 19:16 [PATCH] x86-64: Fix bad assumption that dualcore cpus have synced TSCs john stultz
2005-09-19 19:31 ` Andi Kleen
2005-09-19 19:42 ` john stultz
2005-09-19 19:49 ` [discuss] " Andi Kleen
2005-09-20 18:59 ` john stultz
2005-09-21 4:03 ` Daniel Jacobowitz
2005-09-21 15:15 ` Ray Bryant
2005-09-21 15:04 ` Andi Kleen
2005-09-21 15:46 ` Ray Bryant
2005-09-22 8:00 ` Jonas Oreland
2005-09-21 20:17 ` Andrew Morton
2005-10-07 12:26 ` Vladimir B. Savkin
2005-10-07 12:31 ` Andi Kleen
2005-10-07 14:15 ` Vladimir B. Savkin
2005-10-07 14:21 ` [discuss] " Velu Erwan
2005-10-08 10:11 ` Vladimir B. Savkin
2005-10-10 18:03 ` john stultz
2005-10-10 18:12 ` Vladimir B. Savkin
2005-10-10 18:19 ` Jonas Oreland
2005-10-11 7:35 ` Vladimir B. Savkin
2005-10-11 8:06 ` Andi Kleen [this message]
2005-10-11 16:27 ` Jonas Oreland
2005-10-25 7:35 ` x86-64: Syncing dualcore cpus TSCs Jonas Oreland
2005-10-25 7:42 ` Andi Kleen
2005-10-26 0:05 ` David Lang
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