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    SubjectRe: [GIT PULL] Native Linux KVM tool for 3.1
    On 07/25/2011 09:50 AM, Sasha Levin wrote:
    > Anthony had a talk on last years KVM forum regarding the QEMU threading
    > model (slide:
    > .
    > It was suggested that the KVM part of QEMU is having a hard time
    > achieving the ideal threading model due to its need to support TCG -
    > something which has nothing to do with KVM itself.

    No, it is not having a hard time. The "foot in the door" that Anthony
    mentions has been part of QEMU and qemu-kvm for a long time
    (multi-threading is necessary to support SMP!) and works quite well.

    Historically, there were three main loops:

    1) QEMU single-threaded;

    2) QEMU multi-threaded; clean, but buggy, untested and bitrotting;

    3) qemu-kvm multi-threaded, forked from (1), ugly but robust and widely

    In 0.15 the two multi-threaded versions have been unified by Jan Kiszka.
    I have even ported (2) to Windows with little or no pain; porting to
    Mac OS X interestingly is harder than Windows, because non-portable
    Linux assumptions about signal handling have crept in the code (to
    preempt the objections: they weren't just non-portabilities, they were
    latent bugs). Windows just does not have signals. :)

    So, right now, the only difference is that QEMU is still defaulting to
    the single-threaded main loop, while qemu-kvm enables multi-threading by
    default. In some time even QEMU will switch.

    Yes, this is of course worse than getting it right in the first place;
    Nobody is saying the opposite.


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