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

[Avi Kivity]

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.

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