linux-kernel - Re: [PATCH v2 1/3] KVM: LAPIC: Make lapic timer unpinned when timer is injected by posted-interrupt

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Message-ID: <CANRm+CzgNu7-FOieFqkC3MpnF1GX2dQzfcAuTKAodF4ZdnDmFw@mail.gmail.com>
Date:   Tue, 11 Jun 2019 16:31:51 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [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@...hat.com> wrote:
>
> 2019-06-06 13:31+0800, Wanpeng Li:
> > From: Wanpeng Li <wanpengli@...cent.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@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.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