From: Andi Kleen <ak@suse.de>
To: Andrea Arcangeli <andrea@cpushare.com>
Subject: Re: disable tsc with seccomp
Date: Sat, 5 Nov 2005 17:12:09 +0100
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Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>
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On Saturday 05 November 2005 17:07, Andrea Arcangeli wrote:
> On Sat, Nov 05, 2005 at 04:37:44PM +0100, Andi Kleen wrote:
> > It was useless, you can get exactly the same information by using RDPMC
> > on perfctr 0 which always runs the NMI watchdog and counts all cycles
> > too.
>
> nmi watchdog is off in my system, but it was used to be very slow.

It is normally on on all x86-64 systems.

> Anyway performance counters should be turned off too. They can be turned
> off on a per task basis right? Just switching another cr4 bit or what?

I definitely don't want any code like this in the context switch. It is 
critical and I don't want to pollute fast paths with stuff like this
that nobody needs.

-Andi
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