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From: Peter Zijlstra <peterz@infradead.org>
To: Zhao Forrest <forrest.zhao@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm-devel@lists.sourceforge.net
Subject: Re: Can Linux kernel handle unsynced TSC?
Date: Fri, 29 Feb 2008 15:27:21 +0100	[thread overview]
Message-ID: <1204295241.6243.108.camel@lappy> (raw)
In-Reply-To: <ac8af0be0802290620q208cf4b0sd672cf18594074eb@mail.gmail.com>


On Fri, 2008-02-29 at 22:20 +0800, Zhao Forrest wrote:
> On 2/29/08, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, 2008-02-29 at 16:55 +0800, Zhao Forrest wrote:
> > > Sorry for reposting it.
> > >
> > > For example,
> > > 1 rdtsc() is invoked on CPU0
> > > 2 process is migrated to CPU1, and rdtsc() is invoked on CPU1
> > > 3 if TSC on CPU1 is slower than TSC on CPU0, can kernel guarantee
> > > that the second rdtsc() doesn't return a value smaller than the one
> > > returned by the first rdtsc()?
> >
> > No, rdtsc() goes directly to the hardware. You need a (preferably cheap)
> > clock abstraction layer on top if you need this.
> 
> Thank you for the clarification. I think gettimeofday() is such kind
> of clock abstraction layer, am I right?

Yes, gtod is one such a layer, however it fails the 'cheap' test for
many definitions of cheap.


      reply	other threads:[~2008-02-29 14:27 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-29  8:55 Zhao Forrest
2008-02-29 10:43 ` Peter Zijlstra
2008-02-29 14:20   ` Zhao Forrest
2008-02-29 14:27     ` Peter Zijlstra [this message]

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