Re: [PATCH v3 1/2] KVM: X86: Less kvmclock sync induced vmexits after VM boots

From: Wanpeng Li
Date: Mon Feb 17 2020 - 05:40:33 EST


On Mon, 17 Feb 2020 at 18:36, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> In the progress of vCPUs creation, it queues a kvmclock sync worker to
> the global
> workqueue before each vCPU creation completes. Each worker will be scheduled
> after 300 * HZ delay and request a kvmclock update for all vCPUs and kick them
> out. This is especially worse when scaling to large VMs due to a lot of vmexits.
> Just one worker as a leader to trigger the kvmclock sync request for
> all vCPUs is
> enough.

Sorry for the alignment.

>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fb5d64e..d0ba2d4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9390,8 +9390,9 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
> if (!kvmclock_periodic_sync)
> return;
>
> - schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
> - KVMCLOCK_SYNC_PERIOD);
> + if (kvm->created_vcpus == 1)
> + schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
> + KVMCLOCK_SYNC_PERIOD);
> }
>
> void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
> --
> 2.7.4