Re: [PATCH v2 5/9] KVM: perform a wake_up in kvm_make_all_cpus_request

Andrew Jones
2017-04-27T11:36:55Z

On Wed, Apr 26, 2017 at 10:32:23PM +0200, Radim Krčmář wrote:
> We want to have kvm_make_all_cpus_request() to be an optmized version of
>
> kvm_for_each_vcpu(i, vcpu, kvm) {
> kvm_make_request(vcpu, request);
> kvm_vcpu_kick(vcpu);
> }
>
> and kvm_vcpu_kick() wakes up the target vcpu. We know which requests do
> not need the wake up and use it to optimize the loop.
>
> Thanks to that, this patch doesn't change the behavior of current users
> (the all don't need the wake up) and only prepares for future where the
> wake up is going to be needed.
>
> I think that most requests do not need the wake up, so we would flip the
> bit then.
>
> kvm_vcpu_kick() will get this condition after it is merged with
> kvm_make_request() because we currently don't know which request is being
> kicked.
>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
> virt/kvm/kvm_main.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e5d52b46b531..3772f7dcc72d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -186,6 +186,9 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
> /* Set ->requests bit before we read ->mode. */
> smp_mb__after_atomic();
>
> + if (!(req & KVM_REQUEST_NO_WAKEUP))
> + kvm_vcpu_wake_up(vcpu);
> +
> if (cpus != NULL && cpu != -1 && cpu != me &&
> kvm_vcpu_exiting_guest_mode(vcpu) != OUTSIDE_GUEST_MODE)
> cpumask_set_cpu(cpu, cpus);
> --
> 2.12.2
>

Reviewed-by: Andrew Jones <drjones@redhat.com>