Re: Performance overhead of paravirt_ops on native identified

[H. Peter Anvin]

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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/