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To: mark@grondar.za
Cc: arch@freebsd.org
Subject: Re: new monotime() call for all architectures.
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Date: Fri, 17 Nov 2000 17:05:41 +0900
From: Kenjiro Cho <kjc@csl.sony.co.jp>
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Mark Murray wrote:
> I need a fast-as-possible "time" inside the kernel to help
> speed up the /dev/random device. I say "time", because although
> it needs to be a function of time (preferably accurate and linear),
> it has no need whatsoever to be "real time", so a simple counter
> is quite OK.
> 
> Pentiums, Alphas and IA64's all have a suitable register on chip,
> while I have to make do with nanotime(9) on i386 and i486.
> 
> I have prepared a monotime(9) call for the i386, alpha and ia64
> architectures (patch enclosed). I have been running this for a
> week or two now with promising results (on a Pentium). With
> the exception of the minimum of "glue" (and nanotime on older
> architectures), these functions reduce to one instruction.
> 
> Comments? Suggestions? Nobel Prize nominations? I'd like to
> commit this soonish if possible.

The PCC (Processor Cycle Counter) register on alpha is 64 bits but
only the lower 32 bits is a counter.

-Kenjiro


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