Subj : Re: What is the real costs of LOCK on x86 multiprocesor machine?
To   : comp.programming.threads
From : chris noonan
Date : Sat Jul 30 2005 06:51 am


Oliver S. wrote:
> > I stepped through InterlockedIncrement and there definitely IS lock.
>
> And there are also locks on Enter- and LeaveCriticalSection.
> MS dropped the two versions of this functions win kernel32.dll
> from NT4 to Win2K.

I vaguely remember encountering the LOCK prefix
in one or two places in Microsoft OS code disassembly
(uniprocessor installation). I assumed it was simply
a mistake, something like new routines being hacked
in quickly without them taking the trouble to add
the offsets of the LOCK prefixes to the list to be
NOP'ed out.

Most of my work is done with NT4 SP4. If subsequent
versions retain the LOCK prefix in uniprocessor
mode that is interesting. Obviously Microsoft got
a measurable performance boost by removing the LOCKs
(I do too, in my code) or they wouldn't have taken
the trouble. By the way, the routines I studied most
were heap functions: NtAllocateHeap etc.


Chris

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