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    SubjectRe: [RFC -v4 PATCH 3/3] kvm: use yield_to instead of sleep in kvm_vcpu_on_spin
    On 01/13/2011 08:16 AM, Avi Kivity wrote:

    >> + for (pass = 0; pass< 2&& !yielded; pass++) {
    >> + kvm_for_each_vcpu(i, vcpu, kvm) {
    >> + struct task_struct *task = vcpu->task;
    >> + if (!pass&& i< last_boosted_vcpu) {
    >> + i = last_boosted_vcpu;
    >> + continue;
    >> + } else if (pass&& i> last_boosted_vcpu)
    >> + break;
    >> + if (vcpu == me)
    >> + continue;
    >> + if (!task)
    >> + continue;
    >> + if (waitqueue_active(&vcpu->wq))
    >> + continue;
    >
    > Suppose the vcpu exits at this point, and its task terminates.

    Arghh, good point.

    > I think the first patch needs some reference counting... I'd move it to
    > the outermost KVM_RUN loop to reduce the performance impact.

    I don't see how refcounting from that other thread could
    possibly help, and I now see that the task_struct_cachep
    does not have SLAB_DESTROY_BY_LRU, either :(

    What do you have in mind here that would both work and
    be acceptable to you as KVM maintainer?

    --
    All rights reversed


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