From: Aili Yao <yaoaili126@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: pbonzini@redhat.com, vkuznets@redhat.com, wanpengli@tencent.com,
jmattson@google.com, joro@8bytes.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, yaoaili@kingsoft.com
Subject: Re: [PATCH v2] KVM: LAPIC: Per vCPU control over kvm_can_post_timer_interrupt
Date: Thu, 16 Dec 2021 16:23:03 +0800 [thread overview]
Message-ID: <20211216162303.230dbdaa@gmail.com> (raw)
In-Reply-To: <Ya/s17QDlGZi9COR@google.com>
On Tue, 7 Dec 2021 23:23:03 +0000
Sean Christopherson <seanjc@google.com> wrote:
> On Tue, Nov 23, 2021 at 10:00 PM Wanpeng Li <kernellwp@gmail.com> wrote:
> > ---
> > arch/x86/kvm/lapic.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 759952dd1222..8257566d44c7 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -113,14 +113,13 @@ static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
> >
> > static bool kvm_can_post_timer_interrupt(struct kvm_vcpu *vcpu)
> > {
> > - return pi_inject_timer && kvm_vcpu_apicv_active(vcpu);
> > + return pi_inject_timer && kvm_mwait_in_guest(vcpu->kvm) && kvm_vcpu_apicv_active(vcpu);
>
> As Aili's changelog pointed out, MWAIT may not be advertised to the guest.
>
> So I think we want this? With a non-functional, opinionated refactoring of
> kvm_can_use_hv_timer() because I'm terrible at reading !(a || b).
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 40270d7bc597..c77cb386d03d 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -113,14 +113,25 @@ static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
>
> static bool kvm_can_post_timer_interrupt(struct kvm_vcpu *vcpu)
> {
> - return pi_inject_timer && kvm_vcpu_apicv_active(vcpu);
> + return pi_inject_timer && kvm_vcpu_apicv_active(vcpu) &&
> + (kvm_mwait_in_guest(vcpu) || kvm_hlt_in_guest(vcpu));
> }
>
> bool kvm_can_use_hv_timer(struct kvm_vcpu *vcpu)
> {
> - return kvm_x86_ops.set_hv_timer
> - && !(kvm_mwait_in_guest(vcpu->kvm) ||
> - kvm_can_post_timer_interrupt(vcpu));
> + /*
> + * Don't use the hypervisor timer, a.k.a. VMX Preemption Timer, if the
> + * guest can execute MWAIT without exiting as the timer will stop
> + * counting if the core enters C3 or lower. HLT in the guest is ok as
> + * HLT is effectively C1 and the timer counts in C0, C1, and C2.
> + *
> + * Don't use the hypervisor timer if KVM can post a timer interrupt to
> + * the guest since posted the timer avoids taking an extra a VM-Exit
> + * when the timer expires.
> + */
> + return kvm_x86_ops.set_hv_timer &&
> + !kvm_mwait_in_guest(vcpu->kvm) &&
> + !kvm_can_post_timer_interrupt(vcpu));
> }
> EXPORT_SYMBOL_GPL(kvm_can_use_hv_timer);
>
It seems Sean and Wanpeng are busy with some other more important issues;
So Please let me try to merge Sean, Wanpeng's ideas and suggestions together,also including my opinions
into one possible approach and get it reviewed, Only if others are OK with this;
I will post a new patch for this later today or tomorrow.
Thanks!
--Aili Yao
next prev parent reply other threads:[~2021-12-16 8:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-24 4:54 [PATCH v2] KVM: LAPIC: Per vCPU control over kvm_can_post_timer_interrupt Aili Yao
2021-12-07 23:23 ` Sean Christopherson
2021-12-08 3:36 ` Aili Yao
2021-12-08 10:21 ` Aili Yao
2021-12-09 18:20 ` Sean Christopherson
2021-12-10 3:47 ` Aili Yao
2021-12-16 8:23 ` Aili Yao [this message]
2021-12-16 15:45 ` Sean Christopherson
2021-12-17 2:22 ` Aili Yao
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