Subj : Re: What is the real costs of LOCK on x86 multiprocesor machine?
To   : comp.programming.threads
From : Mirek Fidler
Date : Sat Jul 30 2005 07:47 pm

Joe Seigh wrote:
> Sean Kelly wrote:
> 
>> Joe Seigh wrote:
>>
>>> Statically or dynamically linked code?  The only case I
>>> think you can safely get away with making LOCK optional
>>> is in system dynamically linked libraries that are hardware
>>> configuration specific.  I use LOCK in inlined code since it's
>>> in effect statically linked and you don't know where the code
>>> will eventually execute.
>>
>>
>>
>> What about testing the hardware configuration on startup and setting a
>> global state flag?  Would it be worthwhile to do this and deal with the
>> duplicated asm and branching it would require?
>>
> Depends on whether the global state flag is in cache when you test it
> and whether ia32-64 handles short conditional jumps effectively.  The
> condition means the pipeline stalls until the flag can be tested.

AFAIK not true.  That is what branch prediction is for, is not it?

I believe that in case of testing single flag that never changes, 
actuall amortized branch costs will be lower than one cycle.

Mirek

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