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Name: Stephan Keil
Date: June 17, 2003 at 06:22:33
Subject: Re: Hyperthreading and 'lock' prefix
In Reply To: Re: Hyperthreading and 'lock' prefix by
Oliver on June 17, 2003 at 06:00:12
Text: Thank you for your effort, Oliver.

| > Just the fact: I tried it on HT system (P4 2.8Ghz, Family 15, Model
| > 2, Stepping 7) and it showed that unlocked instruction is not HT-safe
| > (adding lock prefix to cmpxchg fixed thread safety).

I've started a similar thread on http://intel.forums.liveworld.com/forum.jsp?forum=242
and finally got an answer from an Intel HT expert today, who confirms your
observation (for unknown reasons this final post is not yet visible
in the forum :-o). He also explains, that LOCK only locks the
cache, if the affected value is locally cached. So for performance
reasons it might be useful to ensure that the value is cached.

Thanx all for your answers.

Stephan


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