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Subject[RFC v3 07/10] KVM: arm/arm64: Set a background timer to the earliest timer expiration
Date
When scheduling a background timer, consider both of the virtual and
physical timer and pick the earliest expiration time.

Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
---
arch/arm/kvm/arm.c | 3 ++-
virt/kvm/arm/arch_timer.c | 53 +++++++++++++++++++++++++++++++++++------------
2 files changed, 42 insertions(+), 14 deletions(-)

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 0ecd6cf..21c493a 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -300,7 +300,8 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)

int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
{
- return kvm_timer_should_fire(vcpu_vtimer(vcpu));
+ return kvm_timer_should_fire(vcpu_vtimer(vcpu)) ||
+ kvm_timer_should_fire(vcpu_ptimer(vcpu));
}

void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 1b086fd6..89bdb79 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -118,6 +118,35 @@ static u64 kvm_timer_compute_delta(struct arch_timer_context *timer_ctx)
return 0;
}

+static bool kvm_timer_irq_can_fire(struct arch_timer_context *timer_ctx)
+{
+ return !(timer_ctx->cnt_ctl & ARCH_TIMER_CTRL_IT_MASK) &&
+ (timer_ctx->cnt_ctl & ARCH_TIMER_CTRL_ENABLE);
+}
+
+/*
+ * Returns the earliest expiration time in ns among guest timers.
+ * Note that it will return 0 if none of timers can fire.
+ */
+static u64 kvm_timer_earliest_exp(struct kvm_vcpu *vcpu)
+{
+ u64 min_virt = ULLONG_MAX, min_phys = ULLONG_MAX;
+ struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
+ struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
+
+ if (kvm_timer_irq_can_fire(vtimer))
+ min_virt = kvm_timer_compute_delta(vtimer);
+
+ if (kvm_timer_irq_can_fire(ptimer))
+ min_phys = kvm_timer_compute_delta(ptimer);
+
+ /* If none of timers can fire, then return 0 */
+ if ((min_virt == ULLONG_MAX) && (min_phys == ULLONG_MAX))
+ return 0;
+
+ return min(min_virt, min_phys);
+}
+
static enum hrtimer_restart kvm_timer_expire(struct hrtimer *hrt)
{
struct arch_timer_cpu *timer;
@@ -132,7 +161,7 @@ static enum hrtimer_restart kvm_timer_expire(struct hrtimer *hrt)
* PoV (NTP on the host may have forced it to expire
* early). If we should have slept longer, restart it.
*/
- ns = kvm_timer_compute_delta(vcpu_vtimer(vcpu));
+ ns = kvm_timer_earliest_exp(vcpu);
if (unlikely(ns)) {
hrtimer_forward_now(hrt, ns_to_ktime(ns));
return HRTIMER_RESTART;
@@ -142,12 +171,6 @@ static enum hrtimer_restart kvm_timer_expire(struct hrtimer *hrt)
return HRTIMER_NORESTART;
}

-static bool kvm_timer_irq_can_fire(struct arch_timer_context *timer_ctx)
-{
- return !(timer_ctx->cnt_ctl & ARCH_TIMER_CTRL_IT_MASK) &&
- (timer_ctx->cnt_ctl & ARCH_TIMER_CTRL_ENABLE);
-}
-
bool kvm_timer_should_fire(struct arch_timer_context *timer_ctx)
{
u64 cval, now;
@@ -215,26 +238,30 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
+ struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);

BUG_ON(timer_is_armed(timer));

/*
- * No need to schedule a background timer if the guest timer has
+ * No need to schedule a background timer if any guest timer has
* already expired, because kvm_vcpu_block will return before putting
* the thread to sleep.
*/
- if (kvm_timer_should_fire(vtimer))
+ if (kvm_timer_should_fire(vtimer) || kvm_timer_should_fire(ptimer))
return;

/*
- * If the timer is not capable of raising interrupts (disabled or
+ * If both timers are not capable of raising interrupts (disabled or
* masked), then there's no more work for us to do.
*/
- if (!kvm_timer_irq_can_fire(vtimer))
+ if (!kvm_timer_irq_can_fire(vtimer) && !kvm_timer_irq_can_fire(ptimer))
return;

- /* The timer has not yet expired, schedule a background timer */
- timer_arm(timer, kvm_timer_compute_delta(vtimer));
+ /*
+ * The guest timers have not yet expired, schedule a background timer.
+ * Set the earliest expiration time among the guest timers.
+ */
+ timer_arm(timer, kvm_timer_earliest_exp(vcpu));
}

void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
--
1.9.1

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