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Name: james
Date: June 10, 2003 at 04:01:12
Subject: Re: Hyperthreading and 'lock' prefix
In Reply To: Hyperthreading and 'lock' prefix by
Stephan Keil on June 10, 2003 at 02:30:56
Text: | the x86 instruction set supports the 'lock' prefix for various
| instructions (e.g. inc, add) to guarantee atomicity in multiprocessor
| environments, i.e. multiple _physical_ processors. But is this
| prefix also necessary for hyperthreading processors, i.e. two
| logical processors within one physical processor?

Yes.

I mean, how else is virtual processor #2 gonna know
that it shouldn't write to a location that virtual
processor #1 is currently operating on with a read-
modify-write operation?


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