From d35268da66870d733ae763fd7f9b06a1f63f395e Mon Sep 17 00:00:00 2001 From: Christoffer Dall Date: Tue, 25 Aug 2015 19:48:21 +0200 Subject: arm/arm64: KVM: arch_timer: Only schedule soft timer on vcpu_block We currently schedule a soft timer every time we exit the guest if the timer did not expire while running the guest. This is really not necessary, because the only work we do in the timer work function is to kick the vcpu. Kicking the vcpu does two things: (1) If the vpcu thread is on a waitqueue, make it runnable and remove it from the waitqueue. (2) If the vcpu is running on a different physical CPU from the one doing the kick, it sends a reschedule IPI. The second case cannot happen, because the soft timer is only ever scheduled when the vcpu is not running. The first case is only relevant when the vcpu thread is on a waitqueue, which is only the case when the vcpu thread has called kvm_vcpu_block(). Therefore, we only need to make sure a timer is scheduled for kvm_vcpu_block(), which we do by encapsulating all calls to kvm_vcpu_block() with kvm_timer_{un}schedule calls. Additionally, we only schedule a soft timer if the timer is enabled and unmasked, since it is useless otherwise. Note that theoretically userspace can use the SET_ONE_REG interface to change registers that should cause the timer to fire, even if the vcpu is blocked without a scheduled timer, but this case was not supported before this patch and we leave it for future work for now. Signed-off-by: Christoffer Dall --- include/kvm/arm_arch_timer.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/kvm') diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h index e1e4d7c38dda..ef14cc1f1f26 100644 --- a/include/kvm/arm_arch_timer.h +++ b/include/kvm/arm_arch_timer.h @@ -71,5 +71,7 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid); int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value); bool kvm_timer_should_fire(struct kvm_vcpu *vcpu); +void kvm_timer_schedule(struct kvm_vcpu *vcpu); +void kvm_timer_unschedule(struct kvm_vcpu *vcpu); #endif -- cgit v1.2.3