[PATCH v2] KVM: halt-polling: poll if emulated lapic timer will fire soon
From: Wanpeng Li
Date: Thu May 19 2016 - 09:27:17 EST
From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
If an emulated lapic timer will fire soon(in the scope of 10us the
base of dynamic halt-polling, lower-end of message passing workload
latency TCP_RR's poll time < 10us) we can treat it as a short halt,
and poll to wait it fire, the fire callback apic_timer_fn() will set
KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll.
This can avoid context switch overhead and the latency which we wake
up vCPU.
iperf TCP get ~6% bandwidth improvement.
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: David Matlack <dmatlack@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
v1 -> v2:
* add return statement to non-x86 archs
* capture never expire case for x86 (hrtimer is not started)
arch/arm/include/asm/kvm_host.h | 4 ++++
arch/arm64/include/asm/kvm_host.h | 4 ++++
arch/mips/include/asm/kvm_host.h | 4 ++++
arch/powerpc/include/asm/kvm_host.h | 4 ++++
arch/s390/include/asm/kvm_host.h | 4 ++++
arch/x86/kvm/lapic.c | 11 +++++++++++
arch/x86/kvm/lapic.h | 1 +
arch/x86/kvm/x86.c | 5 +++++
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 14 ++++++++++----
10 files changed, 48 insertions(+), 4 deletions(-)
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 4cd8732..a5fd858 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {}
static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
+static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
+{
+ return -1ULL;
+}
static inline void kvm_arm_init_debug(void) {}
static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index d49399d..94e227a 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {}
static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
+static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
+{
+ return -1ULL;
+}
void kvm_arm_init_debug(void);
void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 9a37a10..456bc42 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
+static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
+{
+ return -1ULL;
+}
static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
#endif /* __MIPS_KVM_HOST_H__ */
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index ec35af3..5986c79 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {}
static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
+static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
+{
+ return -1ULL;
+}
#endif /* __POWERPC_KVM_HOST_H__ */
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 37b9017..bdb01a1 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -696,6 +696,10 @@ static inline void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
struct kvm_memory_slot *slot) {}
static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
+static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
+{
+ return -1ULL;
+}
void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index bbb5b28..cfeeac3 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic)
return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE;
}
+u64 apic_get_timer_expire(struct kvm_vcpu *vcpu)
+{
+ struct kvm_lapic *apic = vcpu->arch.apic;
+ struct hrtimer *timer = &apic->lapic_timer.timer;
+
+ if (!hrtimer_active(timer))
+ return -1ULL;
+ else
+ return ktime_to_ns(hrtimer_get_remaining(timer));
+}
+
static inline int apic_lvt_nmi_mode(u32 lvt_val)
{
return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI;
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 891c6da..ee4da6c 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
struct kvm_vcpu **dest_vcpu);
int kvm_vector_to_index(u32 vector, u32 dest_vcpus,
const unsigned long *bitmap, u32 bitmap_size);
+u64 apic_get_timer_expire(struct kvm_vcpu *vcpu);
#endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a8c7ca3..9b5ad99 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu)
struct static_key kvm_no_apic_vcpu __read_mostly;
EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu);
+u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
+{
+ return apic_get_timer_expire(vcpu);
+}
+
int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
{
struct page *page;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b1fa8f1..14d6c23 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target);
void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
+u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu);
void kvm_flush_remote_tlbs(struct kvm *kvm);
void kvm_reload_remote_mmus(struct kvm *kvm);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index dd4ac9d..e4bb30b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR);
static unsigned int halt_poll_ns_shrink;
module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR);
+/* lower-end of message passing workload latency TCP_RR's poll time < 10us */
+static unsigned int halt_poll_ns_base = 10000;
+
/*
* Ordering of locks:
*
@@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
grow = READ_ONCE(halt_poll_ns_grow);
/* 10us base */
if (val == 0 && grow)
- val = 10000;
+ val = halt_poll_ns_base;
else
val *= grow;
@@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
ktime_t start, cur;
DECLARE_SWAITQUEUE(wait);
bool waited = false;
- u64 block_ns;
+ u64 block_ns, delta, remaining;
+ remaining = kvm_arch_timer_remaining(vcpu);
start = cur = ktime_get();
- if (vcpu->halt_poll_ns) {
- ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
+ if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) {
+ ktime_t stop;
+ delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining;
+ stop = ktime_add_ns(ktime_get(), delta);
++vcpu->stat.halt_attempted_poll;
do {
/*
--
1.9.1