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SubjectRe: [PATCH v2 1/3] KVM: LAPIC: Make lapic timer unpinned when timer is injected by posted-interrupt
2019-06-06 13:31+0800, Wanpeng Li:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Make lapic timer unpinned when timer is injected by posted-interrupt,
> the emulated timer can be offload to the housekeeping cpus.
>
> The host admin should fine tuned, e.g. dedicated instances scenario
> w/ nohz_full cover the pCPUs which vCPUs resident, several pCPUs
> surplus for housekeeping, disable mwait/hlt/pause vmexits to occupy
> the pCPUs, fortunately preemption timer is disabled after mwait is
> exposed to guest which makes emulated timer offload can be possible.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/lapic.c | 20 ++++++++++++++++----
> arch/x86/kvm/x86.c | 5 +++++
> arch/x86/kvm/x86.h | 2 ++
> include/linux/sched/isolation.h | 2 ++
> kernel/sched/isolation.c | 6 ++++++
> 5 files changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index fcf42a3..09b7387 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -127,6 +127,12 @@ static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
> return apic->vcpu->vcpu_id;
> }
>
> +static inline bool posted_interrupt_inject_timer_enabled(struct kvm_vcpu *vcpu)
> +{
> + return pi_inject_timer && kvm_vcpu_apicv_active(vcpu) &&
> + kvm_mwait_in_guest(vcpu->kvm);

I'm torn about the mwait dependency. It covers a lot of the targeted
user base, but the relation is convoluted and not fitting perfectly.

What do you think about making posted_interrupt_inject_timer_enabled()
just

pi_inject_timer && kvm_vcpu_apicv_active(vcpu)

and disarming the vmx preemption timer when
posted_interrupt_inject_timer_enabled(), just like we do with mwait now?

Thanks.

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