Since the commit "8003c9ae204e: add APIC Timer periodic/oneshot mode VMX
preemption timer support", a Windows 10 guest has some erratic timer
spikes after few hours. As the uptime of the VM grows the spikes are
larger.
Here the results on a 150000 times 1ms timer without any load:
Before 8003c9ae204e | After 8003c9ae204e
Max 1834us | 86000us
Mean 1100us | 1021us
Deviation 59us | 149us
Here the results on a 150000 times 1ms timer with a cpu-z stress test:
Before 8003c9ae204e | After 8003c9ae204e
Max 32000us | 140000us
Mean 1006us | 1997us
Deviation 140us | 11095us
The current patch partially revert the previous commit by removing the
target timer expectation to go back to the straight hrtimer calls. The
APIC Timer periodic/oneshot mode support is kept because it is necessary
on the new Windows Spring update.
Signed-off-by: Anthoine Bourgeois <anthoine.bourgeois@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/lapic.c | 57 ++++++++++++++++++++++++----------------------------
arch/x86/kvm/lapic.h | 1 -
2 files changed, 26 insertions(+), 32 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 70dcb5548022..d88cf12259ef 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1173,7 +1173,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
static u32 apic_get_tmcct(struct kvm_lapic *apic)
{
- ktime_t remaining, now;
+ ktime_t remaining;
s64 ns;
u32 tmcct;
@@ -1184,8 +1184,7 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
apic->lapic_timer.period == 0)
return 0;
- now = ktime_get();
- remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
+ remaining = hrtimer_get_remaining(&apic->lapic_timer.timer);
if (ktime_to_ns(remaining) < 0)
remaining = 0;
@@ -1465,32 +1464,48 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
static void start_sw_period(struct kvm_lapic *apic)
{
+ ktime_t now;
+
+ /* lapic timer in oneshot or periodic mode */
+ now = ktime_get();
+ apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
+ * APIC_BUS_CYCLE_NS * apic->divide_count;
+
if (!apic->lapic_timer.period)
return;
- if (apic_lvtt_oneshot(apic) &&
- ktime_after(ktime_get(),
- apic->lapic_timer.target_expiration)) {
+ limit_periodic_timer_frequency(apic);
+
+ if (apic_lvtt_oneshot(apic)) {
apic_timer_expired(apic);
return;
}
hrtimer_start(&apic->lapic_timer.timer,
- apic->lapic_timer.target_expiration,
+ ktime_add_ns(now, apic->lapic_timer.period),
HRTIMER_MODE_ABS_PINNED);
+
+ apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
+ PRIx64 ", "
+ "timer initial count 0x%x, period %lldns, "
+ "expire @ 0x%016" PRIx64 ".\n", __func__,
+ APIC_BUS_CYCLE_NS, ktime_to_ns(now),
+ kvm_lapic_get_reg(apic, APIC_TMICT),
+ apic->lapic_timer.period,
+ ktime_to_ns(ktime_add_ns(now,
+ apic->lapic_timer.period)));
}
static void update_target_expiration(struct kvm_lapic *apic, uint32_t old_divisor)
{
- ktime_t now, remaining;
+ ktime_t remaining;
u64 ns_remaining_old, ns_remaining_new;
apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
* APIC_BUS_CYCLE_NS * apic->divide_count;
limit_periodic_timer_frequency(apic);
- now = ktime_get();
- remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
+ remaining = hrtimer_get_remaining(&apic->lapic_timer.timer);
if (ktime_to_ns(remaining) < 0)
remaining = 0;
@@ -1501,15 +1516,10 @@ static void update_target_expiration(struct kvm_lapic *apic, uint32_t old_diviso
apic->lapic_timer.tscdeadline +=
nsec_to_cycles(apic->vcpu, ns_remaining_new) -
nsec_to_cycles(apic->vcpu, ns_remaining_old);
- apic->lapic_timer.target_expiration = ktime_add_ns(now, ns_remaining_new);
}
static bool set_target_expiration(struct kvm_lapic *apic)
{
- ktime_t now;
- u64 tscl = rdtsc();
-
- now = ktime_get();
apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT)
* APIC_BUS_CYCLE_NS * apic->divide_count;
@@ -1520,19 +1530,8 @@ static bool set_target_expiration(struct kvm_lapic *apic)
limit_periodic_timer_frequency(apic);
- apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
- PRIx64 ", "
- "timer initial count 0x%x, period %lldns, "
- "expire @ 0x%016" PRIx64 ".\n", __func__,
- APIC_BUS_CYCLE_NS, ktime_to_ns(now),
- kvm_lapic_get_reg(apic, APIC_TMICT),
- apic->lapic_timer.period,
- ktime_to_ns(ktime_add_ns(now,
- apic->lapic_timer.period)));
-
- apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
+ apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, rdtsc()) +
nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
- apic->lapic_timer.target_expiration = ktime_add_ns(now, apic->lapic_timer.period);
return true;
}
@@ -1541,9 +1540,6 @@ static void advance_periodic_target_expiration(struct kvm_lapic *apic)
{
apic->lapic_timer.tscdeadline +=
nsec_to_cycles(apic->vcpu, apic->lapic_timer.period);
- apic->lapic_timer.target_expiration =
- ktime_add_ns(apic->lapic_timer.target_expiration,
- apic->lapic_timer.period);
}
bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
@@ -2216,7 +2212,6 @@ void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
apic->lapic_timer.tscdeadline = 0;
if (apic_lvtt_oneshot(apic)) {
apic->lapic_timer.tscdeadline = 0;
- apic->lapic_timer.target_expiration = 0;
}
atomic_set(&apic->lapic_timer.pending, 0);
}
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index edce055e9fd7..56823b159e9b 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -19,7 +19,6 @@
struct kvm_timer {
struct hrtimer timer;
s64 period; /* unit: ns */
- ktime_t target_expiration;
u32 timer_mode;
u32 timer_mode_mask;
u64 tscdeadline;
--
2.11.0
