Re: [PATCH] KVM: x86: Use fast path for Xen timer delivery

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 22/09/2023 10:20, David Woodhouse wrote:
From: David Woodhouse <dwmw@xxxxxxxxxxxx>

Most of the time there's no need to kick the vCPU and deliver the timer
event through kvm_xen_inject_timer_irqs(). Use kvm_xen_set_evtchn_fast()
directly from the timer callback, and only fall back to the slow path
when it's necessary to do so.

This gives a significant improvement in timer latency testing (using
nanosleep() for various periods and then measuring the actual time
elapsed).

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
  arch/x86/kvm/xen.c | 17 ++++++++++++++---
  1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 40edf4d1974c..66c4cf93a55c 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -134,12 +134,23 @@ static enum hrtimer_restart xen_timer_callback(struct hrtimer *timer)
  {
  	struct kvm_vcpu *vcpu = container_of(timer, struct kvm_vcpu,
  					     arch.xen.timer);
+	struct kvm_xen_evtchn e;
+	int rc;
+
  	if (atomic_read(&vcpu->arch.xen.timer_pending))
  		return HRTIMER_NORESTART;
- atomic_inc(&vcpu->arch.xen.timer_pending);
-	kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
-	kvm_vcpu_kick(vcpu);
+	e.vcpu_id = vcpu->vcpu_id;
+	e.vcpu_idx = vcpu->vcpu_idx;
+	e.port = vcpu->arch.xen.timer_virq;

Don't you need to check the port for validity? The VMM may not have set it (and hence be delivering timer VIRQ events itself).

  Paul

+	e.priority = KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL;
+
+	rc = kvm_xen_set_evtchn_fast(&e, vcpu->kvm);
+	if (rc == -EWOULDBLOCK) {
+		atomic_inc(&vcpu->arch.xen.timer_pending);
+		kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
+		kvm_vcpu_kick(vcpu);
+	}
return HRTIMER_NORESTART;
  }




[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux