2019-09-05 06:27:43

by Wanpeng Li

Subject: [PATCH 1/2] KVM: LAPIC: Micro optimize IPI latency

From: Wanpeng Li <[email protected]>

This patch optimizes the virtual IPI emulation sequence:

write ICR2 write ICR2
write ICR read ICR2
read ICR ==> send virtual IPI
read ICR2 write ICR
send virtual IPI

It can reduce kvm-unit-tests/vmexit.flat IPI testing latency(from sender
send IPI to sender receive the ACK) from 3319 cycles to 3203 cycles on
SKylake server.

Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/lapic.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 12ade70..34fd299 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1200,10 +1200,8 @@ void kvm_apic_set_eoi_accelerated(struct kvm_vcpu *vcpu, int vector)
}
EXPORT_SYMBOL_GPL(kvm_apic_set_eoi_accelerated);

-static void apic_send_ipi(struct kvm_lapic *apic)
+static void apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
{
- u32 icr_low = kvm_lapic_get_reg(apic, APIC_ICR);
- u32 icr_high = kvm_lapic_get_reg(apic, APIC_ICR2);
struct kvm_lapic_irq irq;

irq.vector = icr_low & APIC_VECTOR_MASK;
@@ -1940,8 +1938,9 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
}
case APIC_ICR:
/* No delay here, so we always clear the pending bit */
- kvm_lapic_set_reg(apic, APIC_ICR, val & ~(1 << 12));
- apic_send_ipi(apic);
+ val &= ~(1 << 12);
+ apic_send_ipi(apic, val, kvm_lapic_get_reg(apic, APIC_ICR2));
+ kvm_lapic_set_reg(apic, APIC_ICR, val);
break;

case APIC_ICR2:
--
2.7.4

2019-09-05 06:48:17

by Wanpeng Li

Subject: [PATCH 2/2] KVM: VMX: Stop the preemption timer during vCPU reset

From: Wanpeng Li <[email protected]>

The hrtimer which is used to emulate lapic timer is stopped during
vcpu reset, preemption timer should do the same.

Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/vmx/vmx.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 570a233..f794929 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4162,6 +4162,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)

vcpu->arch.microcode_version = 0x100000000ULL;
vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
+ vmx->hv_deadline_tsc = -1;
kvm_set_cr8(vcpu, 0);

if (!init_event) {
--
2.7.4

2019-09-11 16:10:14

by Paolo Bonzini

Subject: Re: [PATCH 2/2] KVM: VMX: Stop the preemption timer during vCPU reset

On 05/09/19 08:26, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> The hrtimer which is used to emulate lapic timer is stopped during
> vcpu reset, preemption timer should do the same.
>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> arch/x86/kvm/vmx/vmx.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 570a233..f794929 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4162,6 +4162,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>
> vcpu->arch.microcode_version = 0x100000000ULL;
> vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
> + vmx->hv_deadline_tsc = -1;
> kvm_set_cr8(vcpu, 0);
>
> if (!init_event) {
>

Queued both, thanks.

Paolo