linux-kernel - Re: Can Linux kernel handle unsynced TSC?

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Message-ID: <ac8af0be0802290620q208cf4b0sd672cf18594074eb@mail.gmail.com>
Date:	Fri, 29 Feb 2008 22:20:08 +0800
From:	"Zhao Forrest" <forrest.zhao@...il.com>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, kvm-devel@...ts.sourceforge.net
Subject: Re: Can Linux kernel handle unsynced TSC?

On 2/29/08, Peter Zijlstra <peterz@...radead.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?
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