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    SubjectRe: [PATCH v4 06/10] KVM: MMU: fast path of handling guest page fault
    On Wed, 02 May 2012 13:39:51 +0800
    Xiao Guangrong <> wrote:

    > > Was the problem really mmu_lock contention?

    > Takuya, i am so tired to argue the advantage of lockless write-protect
    > and lockless O(1) dirty-log again and again.

    You are missing my point. Please do not take my comments as an objection
    to your whole work: whey do you feel so?

    I thought that your new fast-page-fault path was fast and optimized
    the guest during dirty logging.

    So in this v4, you might get a similar result even before dropping
    mmu_lock, without 07/10?, if the problem Marcelo explained was not there.

    Of course there is a problem of mmu_lock contention. What I am suggesting
    is to split that problem and do measurement separately so that part of
    your work can be merged soon.

    Your guest size and workload was small to make get_dirty hold mmu_lock
    long time. If you want to appeal the real value of lock-less, you need to
    do another measurment.

    But this is your work and it's up to you. Although I was thinking to help
    your measurement, I cannot do that knowing the fact that you would not
    welcome my help.

    > > Although I am not certain about what will be really needed in the
    > > final form, if this kind of maybe-needed-overhead is going to be
    > > added little by little, I worry about possible regression.

    > Well, will you suggest Linus to reject all patches and stop
    > all discussion for the "possible regression" reason?

    My concern was for Marcelo's examples, not your current implementation.
    If you can show explicitely what will be needed in the final form,
    I do not have any concern.

    Sorry for disturbing.


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