linux-kernel - [PATCH v2] KVM: LAPIC: Retry tune per-vCPU timer_advance

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Date:   Fri,  5 Jul 2019 23:23:42 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH v2] KVM: LAPIC: Retry tune per-vCPU timer_advance_ns if adaptive tuning goes insane

From: Wanpeng Li <wanpengli@...cent.com>

Retry tune per-vCPU timer_advance_ns if adaptive tuning goes insane which 
can happen sporadically in product environment.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
v1 -> v2:
 * retry max 10 times if adaptive tuning goes insane

 arch/x86/kvm/lapic.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 95affa5..bd0dbe5 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1538,6 +1538,7 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
 	u64 ns;
+	uint retry_count = 0;
 
 	/* too early */
 	if (advance_expire_delta < 0) {
@@ -1556,8 +1557,10 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
 	if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
 		apic->lapic_timer.timer_advance_adjust_done = true;
 	if (unlikely(timer_advance_ns > 5000)) {
-		timer_advance_ns = 0;
-		apic->lapic_timer.timer_advance_adjust_done = true;
+		timer_advance_ns = 1000;
+		apic->lapic_timer.timer_advance_adjust_done = false;
+		if (++retry_count > 10)
+			apic->lapic_timer.timer_advance_adjust_done = true;
 	}
 	apic->lapic_timer.timer_advance_ns = timer_advance_ns;
 }
-- 
1.8.3.1