lkml.org 
[lkml]   [2019]   [Jun]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3 2/4] KVM: LAPIC: lapic timer interrupt is injected by posted interrupt
Date
From: Wanpeng Li <wanpengli@tencent.com>

Dedicated instances are currently disturbed by unnecessary jitter due
to the emulated lapic timers fire on the same pCPUs which vCPUs resident.
There is no hardware virtual timer on Intel for guest like ARM. Both
programming timer in guest and the emulated timer fires incur vmexits.
This patch tries to avoid vmexit which is incurred by the emulated
timer fires in dedicated instance scenario.

When nohz_full is enabled in dedicated instances scenario, the emulated
timers can be offload to the nearest busy housekeeping cpus since APICv
is really common in recent years. The guest timer interrupt is injected
by posted-interrupt which is delivered by housekeeping cpu once the emulated
timer fires.

~3% redis performance benefit can be observed on Skylake server.

w/o patch:

VM-EXIT Samples Samples% Time% Min Time Max Time Avg time

EXTERNAL_INTERRUPT 42916 49.43% 39.30% 0.47us 106.09us 0.71us ( +- 1.09% )

w/ patch:

VM-EXIT Samples Samples% Time% Min Time Max Time Avg time

EXTERNAL_INTERRUPT 6871 9.29% 2.96% 0.44us 57.88us 0.72us ( +- 4.02% )

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/lapic.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e57eeba..020599f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -133,6 +133,12 @@ inline bool posted_interrupt_inject_timer_enabled(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_GPL(posted_interrupt_inject_timer_enabled);

+static inline bool can_posted_interrupt_inject_timer(struct kvm_vcpu *vcpu)
+{
+ return posted_interrupt_inject_timer_enabled(vcpu) &&
+ kvm_hlt_in_guest(vcpu->kvm);
+}
+
static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
u32 dest_id, struct kvm_lapic ***cluster, u16 *mask) {
switch (map->mode) {
@@ -1441,6 +1447,19 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
}
}

+static void kvm_apic_inject_pending_timer_irqs(struct kvm_lapic *apic)
+{
+ struct kvm_timer *ktimer = &apic->lapic_timer;
+
+ kvm_apic_local_deliver(apic, APIC_LVTT);
+ if (apic_lvtt_tscdeadline(apic))
+ ktimer->tscdeadline = 0;
+ if (apic_lvtt_oneshot(apic)) {
+ ktimer->tscdeadline = 0;
+ ktimer->target_expiration = 0;
+ }
+}
+
static void apic_timer_expired(struct kvm_lapic *apic)
{
struct kvm_vcpu *vcpu = apic->vcpu;
@@ -1450,6 +1469,11 @@ static void apic_timer_expired(struct kvm_lapic *apic)
if (atomic_read(&apic->lapic_timer.pending))
return;

+ if (can_posted_interrupt_inject_timer(apic->vcpu)) {
+ kvm_apic_inject_pending_timer_irqs(apic);
+ return;
+ }
+
atomic_inc(&apic->lapic_timer.pending);
kvm_set_pending_timer(vcpu);

@@ -2386,13 +2410,7 @@ void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
struct kvm_lapic *apic = vcpu->arch.apic;

if (atomic_read(&apic->lapic_timer.pending) > 0) {
- kvm_apic_local_deliver(apic, APIC_LVTT);
- if (apic_lvtt_tscdeadline(apic))
- apic->lapic_timer.tscdeadline = 0;
- if (apic_lvtt_oneshot(apic)) {
- apic->lapic_timer.tscdeadline = 0;
- apic->lapic_timer.target_expiration = 0;
- }
+ kvm_apic_inject_pending_timer_irqs(apic);
atomic_set(&apic->lapic_timer.pending, 0);
}
}
--
2.7.4
\
 
 \ /
  Last update: 2019-06-11 14:18    [W:0.050 / U:4.584 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site