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 11:43:43 +0100 [thread overview]
Message-ID: <1204281823.6243.78.camel@lappy> (raw)
In-Reply-To: <ac8af0be0802290055m5ca1aa84yad6e38f6935f847@mail.gmail.com>
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.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Zhao Forrest <forrest.zhao@gmail.com>
Cc: kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: Can Linux kernel handle unsynced TSC?
Date: Fri, 29 Feb 2008 11:43:43 +0100 [thread overview]
Message-ID: <1204281823.6243.78.camel@lappy> (raw)
In-Reply-To: <ac8af0be0802290055m5ca1aa84yad6e38f6935f847@mail.gmail.com>
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.
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next prev parent reply other threads:[~2008-02-29 10:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-29 8:55 Can Linux kernel handle unsynced TSC? Zhao Forrest
2008-02-29 8:55 ` Zhao Forrest
2008-02-29 10:43 ` Peter Zijlstra [this message]
2008-02-29 10:43 ` Peter Zijlstra
2008-02-29 14:20 ` Zhao Forrest
2008-02-29 14:20 ` Zhao Forrest
2008-02-29 14:27 ` Peter Zijlstra
2008-02-29 14:27 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2008-02-29 8:43 Zhao Forrest
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