[PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns

[Wanpeng Li]

From: Wanpeng Li <wanpen...@tencent.com>

Even if for realtime CPUs, cache line bounces, frequency scaling, presence 
of higher-priority RT tasks, etc can cause different response. These 
interferences should be considered and periodically revaluate whether 
or not the lapic_timer_advance_ns value is the best, do nothing if it is,
otherwise recaluate again. 

Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Radim Krčmář <rkrc...@redhat.com>
Signed-off-by: Wanpeng Li <wanpen...@tencent.com>
---
 arch/x86/kvm/lapic.c | 16 +++++++++++++++-
 arch/x86/kvm/lapic.h |  1 +
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index df5cd07..8b62008 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_RECALC_PERIOD (600 * HZ)
 
 static inline int apic_test_vector(int vec, void *bitmap)
 {
@@ -1484,6 +1485,17 @@ static inline void adjust_lapic_timer_advance(struct 
kvm_vcpu *vcpu,
        u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
        u64 ns;
 
+       /* periodic revaluate */
+       if (unlikely(apic->lapic_timer.timer_advance_adjust_done)) {
+               apic->lapic_timer.recalc_timer_advance_ns = jiffies +
+                       LAPIC_TIMER_ADVANCE_RECALC_PERIOD;
+               if (abs(advance_expire_delta) > 
LAPIC_TIMER_ADVANCE_ADJUST_DONE) {
+                       timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
+                       apic->lapic_timer.timer_advance_adjust_done = false;
+               } else
+                       return;
+       }
+
        /* too early */
        if (advance_expire_delta < 0) {
                ns = -advance_expire_delta * 1000000ULL;
@@ -1523,7 +1535,8 @@ 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 (unlikely(!apic->lapic_timer.timer_advance_adjust_done) ||
+               time_before(apic->lapic_timer.recalc_timer_advance_ns, jiffies))
                adjust_lapic_timer_advance(vcpu, 
apic->lapic_timer.advance_expire_delta);
 }
 
@@ -2301,6 +2314,7 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int 
timer_advance_ns)
        if (timer_advance_ns == -1) {
                apic->lapic_timer.timer_advance_ns = 
LAPIC_TIMER_ADVANCE_ADJUST_INIT;
                apic->lapic_timer.timer_advance_adjust_done = false;
+               apic->lapic_timer.recalc_timer_advance_ns = jiffies;
        } 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..31ced36 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -31,6 +31,7 @@ struct kvm_timer {
        u32 timer_mode_mask;
        u64 tscdeadline;
        u64 expired_tscdeadline;
+       unsigned long recalc_timer_advance_ns;
        u32 timer_advance_ns;
        s64 advance_expire_delta;
        atomic_t pending;                       /* accumulated triggered timers 
*/
-- 
2.7.4