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SubjectRe: [PATCH v2 1/3] KVM: LAPIC: Make lapic timer unpinned when timer is injected by posted-interrupt
On Tue, 11 Jun 2019 at 01:11, Radim Krčmář <rkrcmar@redhat.com> wrote:
>
> 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?

Agreed, thanks for the review. :)

Regards,
Wanpeng Li

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