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    SubjectRe: [PATCH 00/13] KVM: MMU: fast page fault
    On 04/11/2012 05:14 PM, Takuya Yoshikawa wrote:
    > On Wed, 11 Apr 2012 20:38:57 +0800
    > Xiao Guangrong <> wrote:
    > > Well, my point is that live migration is so very useful that it is worth
    > > to be improved, the description of your also proves this point.
    > >
    > > What is your really want to say but i missed?
    > How to improve and what we should pay for that.
    > Note that I am not objecting to O(1) itself.
    > Do you remember that when we discussed O(1) issue last year, with Avi,
    > the agreement was that we should take more time and look carefully
    > with more measurements to confirm if it's really worthwhile.
    > The point is whether we should do O(1) now, including near future.
    > My opinion is that we should do what we can do now and wait for feedback
    > from real users.
    > Before making the current code stable, I do not want to see it replaced
    > so dramatically. Otherwise when can we use live migration with enough
    > confidence? There may be another subtle bugs we should fix now.
    > In addition, XBRZLE and post-copy is now being developed in QEMU.
    > What do you think about this Avi, Marcelo?

    Currently the main performance bottleneck for migration is qemu, which
    is single threaded and generally inefficient. However I am sure that
    once the qemu bottlenecks will be removed we'll encounter kvm problems,
    particularly with wide (many vcpus) and large (lots of memory) guests.
    So it's a good idea to improve in this area. I agree we'll need to
    measure each change, perhaps with a test program until qemu catches up.

    > I am testing the current live migration to see when and for what it can
    > be used. I really want to see it become stable and usable for real
    > services.

    Well, it's used in production now.

    > > Okay, let us to compare the performance number after O(1) implemented.
    > From my experience, I want to say that live migration is very difficult
    > to say about performance. That is the problem I am now struggling with.
    > I developed dirty-log-perf unit-test for that but that was not enough.
    > Needless to say, checking the correctness is harder.
    > So I really do not want to see drastic change now without any real need
    > or feedback from real users -- this is my point.

    It's a good point, we should avoid change for its own sake.

    error compiling committee.c: too many arguments to function

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