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    SubjectRe: [patch 04/17] Add pagetable accessors to pack and unpack pagetable entries
    Ingo Molnar wrote:
    > the main metric we are interested in is the overhead for people who just
    > want to run the non-patched native kernel that has CONFIG_PARAVIRT
    > enabled (99%+ of the users at the moment), so the delta is:
    >
    > null: +12.0%
    > null IO: +7.5%
    > stat: within noise
    > open/close: within noise
    > TCP: ~5.0%
    > signal install: 2.0%
    > signal handle: 4.7%
    > fork: 2.7%
    > exec: 3.6%
    > shell: 3.6%
    >
    Hm, I don't think you can get this much precision out of these numbers.
    I noticed larger variations from boot-to-boot running the same test.

    > this is not 'barely measurable' but 'BLOODY LARGE' overhead.

    Yes. Fortunately there's a noticable difference between native and
    unpatched paravirt, because it shows all the effort we put into patching
    is worthwhile.

    >> paravirt, patching
    >> ezr Linux 2.6.21- 1000 0.25 0.53 31.8 34.4 10.1 1.04 5.44 730. 1583 4600
    >> ezr Linux 2.6.21- 1000 0.26 0.55 32.1 35.2 13.3 1.03 5.48 748. 1589 4606
    >> ezr Linux 2.6.21- 1000 0.26 0.54 32.0 34.9 14.1 1.04 5.43 752. 1606 4647
    >>
    >
    > i guess this pretty much makes the case for patching ...
    >

    Right, that's why there's patching.


    J
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