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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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