On Thu, May 31, 2012 at 12:27:09PM +0300, Avi Kivity wrote:
> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >> index 953e692..c0209eb 100644
> >> --- a/arch/x86/kvm/x86.c
> >> +++ b/arch/x86/kvm/x86.c
> >> @@ -5232,55 +5232,58 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >> bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
> >> vcpu->run->request_interrupt_window;
> >> bool req_immediate_exit = 0;
> >> + ulong reqs;
> >>
> >> if (unlikely(req_int_win))
> >> kvm_make_request(KVM_REQ_EVENT, vcpu);
> >>
> >> if (vcpu->requests) {
> >> - if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
> >> + reqs = xchg(&vcpu->requests, 0UL);
> >> +
> >> + if (test_bit(KVM_REQ_MMU_RELOAD, &reqs))
> >> kvm_mmu_unload(vcpu);
> >> - if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
> >> + if (test_bit(KVM_REQ_MIGRATE_TIMER, &reqs))
> >> __kvm_migrate_timers(vcpu);
> >> - if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
> >> + if (test_bit(KVM_REQ_CLOCK_UPDATE, &reqs)) {
> >> r = kvm_guest_time_update(vcpu);
> >> if (unlikely(r))
> >> goto out;
> >> }
> >
> > Bailing out loses requests in "reqs".
>
>
> Whoops, good catch.
>
> >
> > Caching the requests makes the following type of sequence behave strangely
> >
> > req = xchg(&vcpu->requests);
> > if request is set
> > request handler
> > ...
> > set REQ_EVENT
> > ...
> >
> > prepare for guest entry
> > vcpu->requests set
> > bail
>
>
> I don't really mind that. But I do want to reduce the overhead of a
> request, they're not that rare in normal workloads.
>
> How about
>
>
> for_each_set_bit(req, &vcpu->requests, BITS_PER_LONG) {
> clear_bit(bit, &vcpu->requests);
> r = request_handlers[bit](vcpu);
> if (r)
> goto out;
> }
>
> ? That makes for O(1) handling since usually we only have one request
> set (KVM_REQ_EVENT). We'll make that the last one to avoid the scenario
> above.
That is better.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
