Zachary Amsden a écrit :
> 
> Yes.  Even then, last time I clocked instructions, xchg was still slower 
> than read / write, although I could be misremembering.  And it's not 
> totally clear that they will always be in cached state, however, and for 
> SMP, we still want to drop the implicit lock in cases where the 
> processor might not know they are cached exclusive, but we know there 
> are no other racing users.  And there are plenty of old processors out 
> there to still make it worthwhile.
> 

Is there one processor that benefit from this patch then ?

I couldnt get a win on my test machines, maybe they are not old enough ;)

umask() doesnt need xchg() atomic semantic. If several threads are using 
umask() concurrently results are not guaranted anyway.