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From: Mikael Pettersson <mikpe@csd.uu.se>
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Date: Fri, 16 Aug 2002 15:19:31 +0200
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Andrea Arcangeli <andrea@suse.de>, john stultz <johnstul@us.ibm.com>,
       Marcelo Tosatti <marcelo@conectiva.com.br>,
       lkml <linux-kernel@vger.kernel.org>, Leah Cunningham <leahc@us.ibm.com>,
       wilhelm.nuesser@sap.com, paramjit@us.ibm.com, msw@redhat.com
Subject: Re: [PATCH] tsc-disable_B9
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Alan Cox writes:
 > On Thu, 2002-08-15 at 17:56, Andrea Arcangeli wrote:
 > > sorry but I don't see the point of badtsc only in kernel.
 > > 
 > > If the TSC is bad that will be in particular bad from userspace where
 > > there's no hope to know what CPU you're running on.
 > 
 > You can still do meaningful measurements for things like profiling
 > because the cpu hop is statistically uninteresting.

There are kernel extensions around that handle process migration across
CPUs while providing virtualised per-process TSC counts, and for which
the TSCs do NOT need to be in perfect sync.

Disabling user-space RDTSC just because the TSCs aren't in sync is stupid.

/Mikael
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