Re: [PATCH v2 4/7] KVM: avoid unnecessary wait for a async pf

Gleb Natapov
2010-11-01T09:25:36Z

On Mon, Nov 01, 2010 at 05:01:28PM +0800, Xiao Guangrong wrote:
> In current code, it checks async pf completion out of the wait context,
> like this:
>
> if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
> !vcpu->arch.apf.halted)
> r = vcpu_enter_guest(vcpu);
> else {
> ......
> kvm_vcpu_block(vcpu)
> ^- waiting until 'async_pf.done' is not empty
> }
>
> kvm_check_async_pf_completion(vcpu)
> ^- delete list from async_pf.done
>
> So, if we check aysnc pf completion first, it can be blocked at
> kvm_vcpu_block
>
> Fixed by mark the vcpu is unhalted in kvm_check_async_pf_completion()
> path
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Acked-by: Gleb Natapov <gleb@redhat.com>

> ---
> arch/x86/kvm/x86.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9b543f4..4da8485 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6280,6 +6280,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
> vcpu->arch.fault.address = work->arch.token;
> kvm_inject_page_fault(vcpu);
> }
> + vcpu->arch.apf.halted = false;
> }
>
> bool kvm_arch_can_inject_async_page_present(struct kvm_vcpu *vcpu)
> --
> 1.7.0.4

--
Gleb.