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Groups > linux.kernel > #1501131
| From | Paolo Bonzini <pbonzini@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry |
| Date | 2016-10-14 20:30 +0200 |
| Message-ID | <ssfp1-4T2-43@gated-at.bofh.it> (permalink) |
| References | <ssfoZ-4T2-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On some benchmarks (e.g. netperf with ioeventfd disabled), APICv
posted interrupts turn out to be slower than interrupt injection via
KVM_REQ_EVENT.
This patch optimizes a bit the IRR update, avoiding expensive atomic
operations in the common case where PI.ON=0 at vmentry or the PIR vector
is mostly zero. This saves at least 20 cycles (1%) per vmexit, as
measured by kvm-unit-tests' inl_from_qemu test (20 runs):
| enable_apicv=1 | enable_apicv=0
| mean stdev | mean stdev
----------|-----------------|------------------
before | 5826 32.65 | 5765 47.09
after | 5809 43.42 | 5777 77.02
Of course, any change in the right column is just placebo effect. :)
The savings are bigger if interrupts are frequent.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/lapic.c | 6 ++++--
arch/x86/kvm/vmx.c | 9 ++++++++-
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 23b99f305382..63a442aefc12 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -342,9 +342,11 @@ void __kvm_apic_update_irr(u32 *pir, void *regs)
u32 i, pir_val;
for (i = 0; i <= 7; i++) {
- pir_val = xchg(&pir[i], 0);
- if (pir_val)
+ pir_val = READ_ONCE(pir[i]);
+ if (pir_val) {
+ pir_val = xchg(&pir[i], 0);
*((u32 *)(regs + APIC_IRR + i * 0x10)) |= pir_val;
+ }
}
}
EXPORT_SYMBOL_GPL(__kvm_apic_update_irr);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2577183b40d9..7c79d6c6b6ed 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -521,6 +521,12 @@ static inline void pi_set_sn(struct pi_desc *pi_desc)
(unsigned long *)&pi_desc->control);
}
+static inline void pi_clear_on(struct pi_desc *pi_desc)
+{
+ clear_bit(POSTED_INTR_ON,
+ (unsigned long *)&pi_desc->control);
+}
+
static inline int pi_test_on(struct pi_desc *pi_desc)
{
return test_bit(POSTED_INTR_ON,
@@ -4854,9 +4860,10 @@ static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- if (!pi_test_and_clear_on(&vmx->pi_desc))
+ if (!pi_test_on(&vmx->pi_desc))
return;
+ pi_clear_on(&vmx->pi_desc);
kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
}
--
1.8.3.1
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[PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
[PATCH 3/5] KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 3/5] KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:10 +0200
[PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Wanpeng Li <kernellwp@gmail.com> - 2016-10-18 08:10 +0200
Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:00 +0200
[PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 21:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Nadav Amit <nadav.amit@gmail.com> - 2016-10-14 21:50 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-15 09:50 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-16 04:40 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-10-19 20:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-27 00:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Nadav Amit <nadav.amit@gmail.com> - 2016-10-14 21:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-16 05:30 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini <pbonzini@redhat.com> - 2016-10-17 13:10 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:00 +0200
Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-26 23:50 +0200
[PATCH 5/5] KVM: vmx: clear pending interrupts on KVM_SET_LAPIC Paolo Bonzini <pbonzini@redhat.com> - 2016-10-14 20:30 +0200
Re: [PATCH 5/5] KVM: vmx: clear pending interrupts on KVM_SET_LAPIC Radim Krčmář <rkrcmar@redhat.com> - 2016-10-26 22:10 +0200
Re: [PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-27 00:00 +0200
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