Re: [Lguest] [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

[Avi Kivity <avi@redhat.com>]

Rusty Russell wrote:
> On Sunday 30 November 2008 04:52:41 Avi Kivity wrote:
>   
>> Alexander van Heukelum wrote:
>>     
>>> I now did the benchmarks for the same -rc6 with hpa's 4-byte stubs
>>> too. Same machine. It's significantly better than the other two
>>> options in terms of speed. It takes about 7% less cpu to handle
>>> the interrupts. (0.64% cpu instead of 0.69%.) I have to run now,
>>> I'll let interpreting the histogram to someone else ;).
>>>       
>> This is noise. 0.05% cpu on a 1GHz machine servicing 1000 interrupt/sec
>> boils down to 500 cycles/interrupt.  These changes shouldn't amount to
>> so much (and I doubt you have 1000 interrupts/sec with a single disk)..
>>     
>
> Sure, but smallest cache wins.  Which is why I thought hpa chose the 3 byte 
> option.
>
>   

Four bytes was the smallest sane option.  Three bytes involved 
instruction opcodes overlap.

>> I'm sorry, but the whole effort is misguided, in my opinion.
>>     
>
> Respectfully disagree.  I wouldn't do it, but it warms my heart that others 
> are.  It's are not subtractive from other optimization efforts.
>   

Once it's done there's no reason not to commit it.  But the effort 
expended to do it is gone, without any measurable return.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.