linux-kernel - Re: RFC: Bogus setting of CONSTANT TSC ?

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Message-ID: <20110313170632.GK2499@one.firstfloor.org>
Date:	Sun, 13 Mar 2011 18:06:32 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Dave Jones <davej@...hat.com>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: RFC: Bogus setting of CONSTANT TSC ?

> This was initially introduced with commit 39b3a7 ([PATCH] i386/x86-64:
> Generalize X86_FEATURE_CONSTANT_TSC flag), though the changelog is
> utterly useless. Andi ??

Only Nehalem and beyond set the 8000_0007 flag, but Intel has had a constant
TSC since Yonah. That is what this logic implements.

However on Nehalem and beyond if the 8000_0007 is clear the BIOS wants
to tell us that it knows the system doesn't have a synchronized TSC.
This is currently still broken, but the timer watchdog usually catches
it later. It only affects a few relatively obscure systems.

-Andi
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