linux-kernel - Re: [PATCH] x86: Export tsc related information in sysfs

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Message-ID: <4BF2C881.60807@zytor.com>
Date:	Tue, 18 May 2010 10:04:01 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Andi Kleen <andi@...stfloor.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Ingo Molnar <mingo@...e.hu>, chris.mason@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Export tsc related information in sysfs

On 05/18/2010 09:52 AM, Peter Zijlstra wrote:
> On Tue, 2010-05-18 at 09:40 -0700, H. Peter Anvin wrote:
>>
>> The problem is that you throw the baby (vsyscall) out with the bathwater
>> (user rdtsc). 
> 
> Well, we could only flip the CR4 bit when we mark the TSC unsuitable for
> gtod. That should be plenty good to tag all userspace trying to use it,
> since more than half my machines don't use TSC for clocksource.

This might be an option, although it would have to be an *option*.
There are restricted uses of the TSC in userspace which are still useful
(mainly involving performance analysis and/or CPU-locked processes).

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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