linux-kernel - Re: [PATCH 1/3] Add prctl commands PR_GET_TSC and PR_SET

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Message-ID: <480272BD.9010404@zytor.com>
Date:	Sun, 13 Apr 2008 13:53:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Erik Bosman <ejbosman@...vu.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrea Arcangeli <andrea@...share.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Add prctl commands PR_GET_TSC and PR_SET_TSC

Andi Kleen wrote:
>> I think what Erik is trying to do is to make it possible to disable as
>> many of these in the kernel as possible; I/O is easy, it's off by
>> default; RDTSC and RDPMC can be disabled in the kernel, and I think
>> even XSTORE can be disabled.
> 
> I'm a little sceptical it will work reliably, but we'll see.
> 
> There's also LSL (forgot that earlier). It is used by the vgetcpu()
> because it's faster than CPUID or RDTSCP. Kernel
> sets a magic segment up which has different limits for different CPUs.
> 

Yeah, that's unlikely to be found in code that isn't actively looking 
for it, though.

	-hpa
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