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Subject: Re: OT: P4- 3 GHz with hyper-threading

Author: Eugene Nalimov

Date: 09:33:00 10/30/02

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On October 30, 2002 at 10:53:58, Robert Hyatt wrote:

>On October 30, 2002 at 06:59:21, Terje Vagle wrote:
>
>>Hi all,
>>
>>The new cpu from intel will have a new function called
>>hyper-threading.
>>
>>This will make the operating system able to recognize the cpu as if it was
>>2 cpu's.
>>
>>Could the programs with smp-support make use of this?
>>
>>Regards,
>>
>>Terje Vagle
>
>
>Yes, but it is going to cause some problems.  You don't _really_ have two cpus.
>You
>have a single cpu executing two threads, and when one thread "blocks" waiting on
>a
>memory access or anything else (FP result) then the other thread will run.
>
>Spinlocks will wreck this however...

There is special new instruction PAUSE for such a spinlocks. It is handled as
NOP on all existing (Intel and non-Intel) x86 CPUs prior to P4. It suspends a
(hyper)thread on P4 CPU for undisclosed amount of clock cycles.

Thanks,
Eugene



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