linux-kernel - Re: [PATCH] remove sched notifier for cross-cpu migrations

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Message-ID: <20130711095249.GA25631@dyad.programming.kicks-ass.net>
Date:	Thu, 11 Jul 2013 11:52:49 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	mingo@...hat.com, gleb@...hat.com, glommer@...allels.com,
	tglx@...utronix.de, jeremy@...p.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] remove sched notifier for cross-cpu migrations

On Wed, Jul 10, 2013 at 10:21:57PM -0300, Marcelo Tosatti wrote:
> 
> Linux as a guest on KVM hypervisor, the only user of the pvclock      
> vsyscall interface, does not require notification on task migration 
> because:
> 
> 1. cpu ID number maps 1:1 to per-CPU pvclock time info.
> 2. per-CPU pvclock time info is updated if the
>    underlying CPU changes.
> 3. that version is increased whenever underlying CPU 
>    changes.
> 
> Which is sufficient to guarantee nanoseconds counter
> is calculated properly.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

Awesome, thanks!

Acked-by: Peter Zijlstra <peterz@...radead.org>
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