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Subject[PATCH v4] KVM: LAPIC: Tune lapic_timer_advance_ns smoothly
Date
From: Wanpeng Li <wanpengli@tencent.com>

Filter out drastic fluctuation and random fluctuation, remove
timer_advance_adjust_done altogether, the adjustment would be
continuous.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/lapic.c | 26 ++++++++++++--------------
arch/x86/kvm/lapic.h | 1 -
arch/x86/kvm/x86.c | 2 +-
arch/x86/kvm/x86.h | 1 +
4 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index dbbe478..2585b86 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -69,6 +69,7 @@
#define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000
/* step-by-step approximation to mitigate fluctuation */
#define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8
+#define LAPIC_TIMER_ADVANCE_FILTER 5000

static inline int apic_test_vector(int vec, void *bitmap)
{
@@ -1482,29 +1483,28 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
s64 advance_expire_delta)
{
struct kvm_lapic *apic = vcpu->arch.apic;
- u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
- u64 ns;
+ u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns, ns;
+
+ if (abs(advance_expire_delta) > LAPIC_TIMER_ADVANCE_FILTER ||
+ abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) {
+ /* filter out random fluctuations */
+ return;
+ }

/* too early */
if (advance_expire_delta < 0) {
ns = -advance_expire_delta * 1000000ULL;
do_div(ns, vcpu->arch.virtual_tsc_khz);
- timer_advance_ns -= min((u32)ns,
- timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
+ timer_advance_ns -= ns/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
} else {
/* too late */
ns = advance_expire_delta * 1000000ULL;
do_div(ns, vcpu->arch.virtual_tsc_khz);
- timer_advance_ns += min((u32)ns,
- timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
+ timer_advance_ns += ns/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
}

- if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
- apic->lapic_timer.timer_advance_adjust_done = true;
- if (unlikely(timer_advance_ns > 5000)) {
+ if (unlikely(timer_advance_ns > 5000))
timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
- apic->lapic_timer.timer_advance_adjust_done = false;
- }
apic->lapic_timer.timer_advance_ns = timer_advance_ns;
}

@@ -1524,7 +1524,7 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
if (guest_tsc < tsc_deadline)
__wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);

- if (unlikely(!apic->lapic_timer.timer_advance_adjust_done))
+ if (lapic_timer_advance_ns == -1)
adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta);
}

@@ -2302,10 +2302,8 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
apic->lapic_timer.timer.function = apic_timer_fn;
if (timer_advance_ns == -1) {
apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
- apic->lapic_timer.timer_advance_adjust_done = false;
} else {
apic->lapic_timer.timer_advance_ns = timer_advance_ns;
- apic->lapic_timer.timer_advance_adjust_done = true;
}


diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 50053d2..2aad7e2 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -35,7 +35,6 @@ struct kvm_timer {
s64 advance_expire_delta;
atomic_t pending; /* accumulated triggered timers */
bool hv_timer_in_use;
- bool timer_advance_adjust_done;
};

struct kvm_lapic {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 83288ba..bb4574c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -141,7 +141,7 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
* advancement entirely. Any other value is used as-is and disables adaptive
* tuning, i.e. allows priveleged userspace to set an exact advancement time.
*/
-static int __read_mostly lapic_timer_advance_ns = -1;
+int __read_mostly lapic_timer_advance_ns = -1;
module_param(lapic_timer_advance_ns, int, S_IRUGO | S_IWUSR);

static bool __read_mostly vector_hashing = true;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index b5274e2..1bf2d82 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -301,6 +301,7 @@ extern unsigned int min_timer_period_us;

extern bool enable_vmware_backdoor;

+extern int lapic_timer_advance_ns;
extern int pi_inject_timer;

extern struct static_key kvm_no_apic_vcpu;
--
2.7.4
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