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Date: Tue, 17 Dec 2002 12:16:56 -0800
From: "H. Peter Anvin" <hpa@transmeta.com>
Organization: Transmeta Corporation
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: "Martin J. Bligh" <mbligh@aracnet.com>,
       Linus Torvalds <torvalds@transmeta.com>,
       Dave Jones <davej@codemonkey.org.uk>, Ingo Molnar <mingo@elte.hu>,
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Subject: Re: Intel P6 vs P7 system call performance
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Alan Cox wrote:
> On Tue, 2002-12-17 at 19:26, Martin J. Bligh wrote:
> 
>>>>It's not as good as a pure user-mode solution using tsc could be, but
>>
>>You can't use the TSC to do gettimeofday on boxes where they aren't 
>>syncronised anyway though. That's nothing to do with vsyscalls, you just
>>need a different time source (eg the legacy stuff or HPET/cyclone).
> 
> 
> Ditto all the laptops and the like. With code provided by the kernel we
> can cheat however. If we know the fastest the CPU can go (ie full speed
> on spudstop/powernow etc) we can tell the tsc value at which we have to
> query the kernel to get time to any given accuracy, so allowing limited
> caching
> 
> Ditto by knowing the worst case drift on summit
> 

Clever.  I like it :)

	-hpa


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