From: Wanpeng Li <[email protected]>
This patch implements handle preemption timer fastpath, after timer fire
due to VMX-preemption timer counts down to zero, handle it as soon as
possible and vmentry immediately without checking various kvm stuff when
possible.
Testing on SKX Server.
cyclictest in guest(w/o mwait exposed, adaptive advance lapic timer is default -1):
5632.75ns -> 4559.25ns, 19%
kvm-unit-test/vmexit.flat:
w/o APICv, w/o advance timer:
tscdeadline_immed: 4780.75 -> 3851 19.4%
tscdeadline: 7474 -> 6528.5 12.7%
w/o APICv, w/ adaptive advance timer default -1:
tscdeadline_immed: 4845.75 -> 3930.5 18.9%
tscdeadline: 6048 -> 5871.75 3%
w/ APICv, w/o avanced timer:
tscdeadline_immed: 2919 -> 2467.75 15.5%
tscdeadline: 5661.75 -> 5188.25 8.4%
w/ APICv, w/ adaptive advance timer default -1:
tscdeadline_immed: 3018.5 -> 2561 15.2%
tscdeadline: 4663.75 -> 4626.5 1%
Tested-by: Haiwei Li <[email protected]>
Cc: Haiwei Li <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/vmx/vmx.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7688e40..623c4a0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6593,12 +6593,53 @@ static void vmx_fast_deliver_interrupt(struct kvm_vcpu *vcpu)
}
}
+static void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu);
+
+static enum exit_fastpath_completion handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+ struct kvm_lapic *apic = vcpu->arch.apic;
+ struct kvm_timer *ktimer = &apic->lapic_timer;
+
+ if (vmx_event_needs_reinjection(vcpu))
+ return EXIT_FASTPATH_NONE;
+
+ if (!vmx->req_immediate_exit &&
+ !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
+ if (!vmx_interrupt_allowed(vcpu) ||
+ !apic_lvtt_tscdeadline(apic) ||
+ vmx->rmode.vm86_active ||
+ is_smm(vcpu) ||
+ !kvm_apic_hw_enabled(apic))
+ return EXIT_FASTPATH_NONE;
+
+ if (!apic->lapic_timer.hv_timer_in_use)
+ return EXIT_FASTPATH_CONT_RUN;
+
+ WARN_ON(swait_active(&vcpu->wq));
+ vmx_cancel_hv_timer(vcpu);
+ apic->lapic_timer.hv_timer_in_use = false;
+
+ if (atomic_read(&apic->lapic_timer.pending))
+ return EXIT_FASTPATH_CONT_RUN;
+
+ ktimer->expired_tscdeadline = ktimer->tscdeadline;
+ vmx_fast_deliver_interrupt(vcpu);
+ ktimer->tscdeadline = 0;
+ return EXIT_FASTPATH_CONT_RUN;
+ }
+
+ return EXIT_FASTPATH_NONE;
+}
+
static enum exit_fastpath_completion vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
{
if (!is_guest_mode(vcpu)) {
switch(to_vmx(vcpu)->exit_reason) {
case EXIT_REASON_MSR_WRITE:
return handle_fastpath_set_msr_irqoff(vcpu);
+ case EXIT_REASON_PREEMPTION_TIMER:
+ return handle_fastpath_preemption_timer(vcpu);
default:
return EXIT_FASTPATH_NONE;
}
--
2.7.4
On 21/04/20 13:20, Wanpeng Li wrote:
> +
> + if (!vmx->req_immediate_exit &&
> + !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
> + if (!vmx_interrupt_allowed(vcpu) ||
> + !apic_lvtt_tscdeadline(apic) ||
> + vmx->rmode.vm86_active ||
> + is_smm(vcpu) ||
> + !kvm_apic_hw_enabled(apic))
> + return EXIT_FASTPATH_NONE;
> +
> + if (!apic->lapic_timer.hv_timer_in_use)
> + return EXIT_FASTPATH_CONT_RUN;
> +
> + WARN_ON(swait_active(&vcpu->wq));
> + vmx_cancel_hv_timer(vcpu);
> + apic->lapic_timer.hv_timer_in_use = false;
> +
> + if (atomic_read(&apic->lapic_timer.pending))
> + return EXIT_FASTPATH_CONT_RUN;
> +
> + ktimer->expired_tscdeadline = ktimer->tscdeadline;
> + vmx_fast_deliver_interrupt(vcpu);
> + ktimer->tscdeadline = 0;
> + return EXIT_FASTPATH_CONT_RUN;
> + }
> +
Can you explain all the checks you have here, and why you need something
more complex than apic_timer_expired (possibly by adding some
optimizations to kvm_apic_local_deliver)? This code is impossible to
maintain.
Paolo
On Tue, 21 Apr 2020 at 19:40, Paolo Bonzini <[email protected]> wrote:
>
> On 21/04/20 13:20, Wanpeng Li wrote:
> > +
> > + if (!vmx->req_immediate_exit &&
> > + !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
> > + if (!vmx_interrupt_allowed(vcpu) ||
For non-APICv case, we need to request interrupt-window.
> > + !apic_lvtt_tscdeadline(apic) ||
Now just add fastpath for tscdeadline mode.
> > + vmx->rmode.vm86_active ||
> > + is_smm(vcpu) ||
> > + !kvm_apic_hw_enabled(apic))
These stuff can be removed, kvm_apic_hw_enable() is check in
vmx_fast_deliver_interrupt().
> > + return EXIT_FASTPATH_NONE;
> > +
> > + if (!apic->lapic_timer.hv_timer_in_use)
> > + return EXIT_FASTPATH_CONT_RUN;
> > +
> > + WARN_ON(swait_active(&vcpu->wq));
> > + vmx_cancel_hv_timer(vcpu);
> > + apic->lapic_timer.hv_timer_in_use = false;
> > +
> > + if (atomic_read(&apic->lapic_timer.pending))
> > + return EXIT_FASTPATH_CONT_RUN;
Other two checks are the same in kvm_lapic_expired_hv_timer().
Wanpeng
> > +
> > + ktimer->expired_tscdeadline = ktimer->tscdeadline;
> > + vmx_fast_deliver_interrupt(vcpu);
> > + ktimer->tscdeadline = 0;
> > + return EXIT_FASTPATH_CONT_RUN;
> > + }
> > +
>
> Can you explain all the checks you have here, and why you need something
> more complex than apic_timer_expired (possibly by adding some
> optimizations to kvm_apic_local_deliver)? This code is impossible to
> maintain.
>
> Paolo
>