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SubjectRe: X15 alpha release: as fast as TUX but in user space (fwd)
At 12:29 AM -0700 2001-04-30, H. Peter Anvin wrote:
>"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

The Pentium III TSC has the bizarre characteristic, per Intel docs
anyway, that only the low half can be written (as I recall the high
half gets set to zero), making restoration problematical in certain
power-management regimes. Hopefully the Crusoe does better.
/Jonathan Lundell.
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