lkml.org 
[lkml]   [2019]   [Sep]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH RESEND v3 1/5] KVM: LAPIC: Tune lapic_timer_advance_ns smoothly
Date
From: Wanpeng Li <wanpengli@tencent.com>

Using a moving average based on per-vCPU lapic_timer_advance_ns to tune
smoothly, filter out drastic fluctuation which prevents this before,
let's assume it is 10000 cycles.

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 | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e904ff0..2f4a48a 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 10000

static inline int apic_test_vector(int vec, void *bitmap)
{
@@ -1484,23 +1485,28 @@ 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)
+ /* filter out drastic 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;
} 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;
}

+ timer_advance_ns = (apic->lapic_timer.timer_advance_ns *
+ (LAPIC_TIMER_ADVANCE_ADJUST_STEP - 1) + advance_expire_delta) /
+ 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)) {
--
2.7.4
\
 
 \ /
  Last update: 2019-09-06 03:30    [W:0.054 / U:28.668 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site