Re: [PATCH RT 00/02] SLOB optimizations

[Eric Dumazet]

George Anzinger a écrit :
> > that's just the profiling interrupt hitting them. You should not 
> > analyze irq-safe code with a non-NMI profiling interrupt.
> >
> > CLI/STI is extremely fast. (In fact in the -rt tree i'm using them 
> > within mutexes instead of preempt_enable()/preempt_disable(), because 
> > they are faster and generate less register side-effect.)
> Hm... I rather thought that the cli would cause a rather large hit on 
> the pipeline and certainly on OOE.  Is your observation based on any 
> particular instruction stream?  Sti, on the otherhand should be fast...

Just to be exact, the 'cli' is coded as 3 instruction :

pushfq
popq (%rsp)
cli

and the 'sti' is coded as 2 instructions :
pushq (%rsp)
popfq

And 'popfq' seems to be expensive, at least on Opteron machines and if 
oprofile is not completely wrong...

Eric
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