linux-kernel - [PATCH] KVM: LAPIC: Loose fluctuation filter for auto tune lapic_timer_advance

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Message-Id: <1569390424-22031-1-git-send-email-wanpengli@tencent.com>
Date:   Wed, 25 Sep 2019 13:47:04 +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>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH] KVM: LAPIC: Loose fluctuation filter for auto tune lapic_timer_advance_ns

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

5000 guest cycles delta is easy to encounter on desktop, per-vCPU 
lapic_timer_advance_ns always keeps at 1000ns initial value, lets 
loose fluctuation filter a bit to make auto tune can make some 
progress.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/lapic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 3a3a685..258407e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -67,7 +67,7 @@
 
 static bool lapic_timer_advance_dynamic __read_mostly;
 #define LAPIC_TIMER_ADVANCE_ADJUST_MIN 100
-#define LAPIC_TIMER_ADVANCE_ADJUST_MAX 5000
+#define LAPIC_TIMER_ADVANCE_ADJUST_MAX 10000
 #define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000
 /* step-by-step approximation to mitigate fluctuation */
 #define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8
@@ -1504,7 +1504,7 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
 		timer_advance_ns += ns/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
 	}
 
-	if (unlikely(timer_advance_ns > LAPIC_TIMER_ADVANCE_ADJUST_MAX))
+	if (unlikely(timer_advance_ns > LAPIC_TIMER_ADVANCE_ADJUST_MAX/2))
 		timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
 	apic->lapic_timer.timer_advance_ns = timer_advance_ns;
 }
-- 
2.7.4