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    SubjectRe: [PATCH 3/3] x86, extable: Handle early exceptions
    On 04/19/2012 01:17 PM, David Daney wrote:
    > On 04/19/2012 11:55 AM, H. Peter Anvin wrote:
    >> Either way I suggest picking up David's presorting patchset since it
    >> is already done and use its infrastructure for any further improvements.
    >
    > It does have the advantage of already being implemented. There was a
    > little feedback on the kbuild portions of the patch.
    >
    > If you would like, I will send an updated version of the patch.

    Please. It gets us 90% of the way, and we need the infrastructure
    anyway to do any further work.

    >> As far as a linear probe you get an average of n lookups with a
    >> packing density of 1-1/n so you are right; a linear probe with a
    >> density of say 1/2 is probably best.
    >>
    >
    > I usually see exception table sizes on the order of 2^10 entries, so I
    > have to wonder how much you really gain from an O(1) implementation.

    Well, for either variant of hash table you end up with ~2 serial memory
    references as opposed to ~11. No idea if there are workloads where this
    actually matters.

    -hpa



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