[Xen-devel] Re: Performance overhead of paravirt_ops on native identified

["H. Peter Anvin" <hpa@xxxxxxxxx>]

Xin, Xiaohui wrote:
> Remember we have done one experiment with "jump", the result shows seems the 
> overhead is even more than the call.

I didn't, no.  That seems extremely weird to me.

(Unbalancing the call/ret stack is known to suck royally, of course.)

>>>
>>>     
>> Can't those calls be changed to jumps?
>>   
> 
> In this specific instance of this example, yes.  But if you start 
> enabling various spinlock debug options then there'll be code following 
> the call.  It would be hard for the runtime patching machinery to know 
> when it would be safe to do the substitution.
> 

When there is code after the call, it's rather obviously not safe.

        -hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.


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