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