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From: "H. Peter Anvin" <hpa@transmeta.com>
Message-ID: <3AED145F.84E95D8D@transmeta.com>
Date: Mon, 30 Apr 2001 00:29:35 -0700
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To: "David S. Miller" <davem@redhat.com>
CC: dean gaudet <dean-list-linux-kernel@arctic.org>,
        Jeff Garzik <jgarzik@mandrakesoft.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: X15 alpha release: as fast as TUX but in user space (fwd)
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"David S. Miller" wrote:
> 
> dean gaudet writes:
>  > i was kind of solving a different problem with the code page though -- the
>  > ability to use rdtsc on SMP boxes with processors of varying speeds and
>  > synchronizations.
> 
> A better way to solve that problem is the way UltraSPARC-III do and
> future ia64 systems will, by way of a "system tick" register which
> increments at a constant rate regardless of how the cpus are clocked.
> 
> The "system tick" pulse goes into the processor, so it's still a local
> cpu register being accessed.  Think of it as a system bus clock cycle
> counter.
> 
> Granted, you probably couldn't make changes to the hardware you were
> working on at the time :-)
> 

RDTSC in Crusoe processors does basically this.

	-hpa

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
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