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Date: Wed, 19 Jun 2002 15:58:44 +0200 (MET DST)
From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
To: Mikael Pettersson <mikpe@csd.uu.se>
cc: johnstul@us.ibm.com, kai@tp1.ruhr-uni-bochum.de, Martin.Bligh@us.ibm.com,
       davej@suse.de, linux-kernel@vger.kernel.org, marcelo@conectiva.com.br
Subject: Re: [Patch] tsc-disable_A5
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Message-ID: <Pine.GSO.3.96.1020619145508.15094H-100000@delta.ds2.pg.gda.pl>
Organization: Technical University of Gdansk
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On Sat, 15 Jun 2002, Mikael Pettersson wrote:

> I disagree with Alan's recommendation.

 So do I.

> The real problem is that the kernel confuses a CPU-level property
> (do the CPUs have TSCs?) with a system-level property (are the
> TSCs present and in sync?). CONFIG_X86_TSC really describes the
> latter property, for the former we have the cpu_has_tsc() macro.

 Well, CONFIG_X86_TSC simply asserts we have TSCs present and in sync and
cpu_has_tsc is a run-time check for the same.  The X86_FEATURE_TSC bit
shouldn't be set (and e.g. "notsc" takes care of this) unless TSCs work
correctly as it's both used internally and exported to the userland.  For
low-level fiddling with TSCs one can use cpuid either directly or with the
cpuid driver. 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +

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