From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Subject: [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns
Date: Fri, 9 Aug 2019 13:45:31 +0800 [thread overview]
Message-ID: <1565329531-12327-1-git-send-email-wanpengli@tencent.com> (raw)
From: Wanpeng Li <wanpengli@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 <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@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
next reply other threads:[~2019-08-09 5:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 5:45 Wanpeng Li [this message]
2019-08-09 10:24 ` [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns Paolo Bonzini
2019-08-12 9:06 ` Wanpeng Li
2019-08-14 12:50 ` Paolo Bonzini
2019-08-15 4:04 ` Wanpeng Li
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