On 22/09/2023 10:29, David Woodhouse wrote:
On Fri, 2023-09-22 at 10:22 +0100, Paul Durrant wrote:
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).
Nah, the kvm_xen_timer_enabled() check which gates all the kernel
interception of timer hypercalls is already testing precisely that.
If the TIMER_VIRQ isn't set, none of this code runs. And when userspace
tears down TIMER_VIRQ, the hrtimer is cancelled. So none of this code
(then) runs.
Ok. Good :-)
Reviewed-by: Paul Durrant <paul@xxxxxxx>
