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    SubjectRe: [PATCH 02/11] Add "handle page fault" PV helper.
    On 11/08/2009 04:51 AM, Ingo Molnar wrote:
    >
    > * Avi Kivity <avi@redhat.com> wrote:
    >
    >> On 11/08/2009 01:36 PM, Ingo Molnar wrote:
    >>>> Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two
    >>>> of them kmemcheck, mmiotrace are enabled only for debugging, should
    >>>> not be performance concern. And notifier call sites (two of them)
    >>>> are deliberately, as explained by comment, not at the function entry,
    >>>> so can't be unified with others. (And kmemcheck also has two different
    >>>> call site BTW)
    >>>
    >>> We want mmiotrace to be generic distro capable so the overhead when
    >>> the hook is not used is of concern.
    >>
    >> Maybe we should generalize paravirt-ops patching in case if (x) f() is
    >> deemed too expensive.
    >
    > Yes, that's a nice idea. We have quite a number of 'conditional
    > callbacks' in various critical paths that could be made lighter via such
    > a technique.
    >
    > It would also free new callbacks from the 'it increases overhead even if
    > unused' criticism and made it easier to add them.
    >

    There are a number of other things were we permanently bind to a single
    instance of something, too. Optimizing those away would be nice.
    Consider memcpy(), where we may want to have different implementations
    for different processors.

    -hpa


    --
    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.



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