Re: [PATCH v4 4/5] KVM: LAPIC: Delay trace advance expire delta

[Paolo Bonzini]

On 20/05/19 13:36, Wanpeng Li wrote:
>> Hmm, yeah, that makes sense.  The location of the tracepoint is a bit
>> weird, but I guess we can add a comment in the code.
> Do you need me to post a new patchset? :)

No problem.  The final patch that I committed is this:

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index c12b090f4fad..f8615872ae64 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1502,27 +1502,27 @@ static inline void __wait_lapic_expire(struct kvm_vcpu 
*vcpu, u64 guest_cycles)
 }
 
 static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
-                                             u64 guest_tsc, u64 tsc_deadline)
+                                             s64 advance_expire_delta)
 {
        struct kvm_lapic *apic = vcpu->arch.apic;
        u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
        u64 ns;
 
        /* too early */
-       if (guest_tsc < tsc_deadline) {
-               ns = (tsc_deadline - guest_tsc) * 1000000ULL;
+       if (advance_expire_delta < 0) {
+               ns = -advance_expire_delta * 1000000ULL;
                do_div(ns, vcpu->arch.virtual_tsc_khz);
                timer_advance_ns -= min((u32)ns,
                        timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
        } else {
        /* too late */
-               ns = (guest_tsc - tsc_deadline) * 1000000ULL;
+               ns = advance_expire_delta * 1000000ULL;
                do_div(ns, vcpu->arch.virtual_tsc_khz);
                timer_advance_ns += min((u32)ns,
                        timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
        }
 
-       if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
+       if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
                apic->lapic_timer.timer_advance_adjust_done = true;
        if (unlikely(timer_advance_ns > 5000)) {
                timer_advance_ns = 0;
@@ -1545,13 +1545,13 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu)
        tsc_deadline = apic->lapic_timer.expired_tscdeadline;
        apic->lapic_timer.expired_tscdeadline = 0;
        guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
-       trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline);
+       apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline;
 
        if (guest_tsc < tsc_deadline)
                __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
 
        if (unlikely(!apic->lapic_timer.timer_advance_adjust_done))
-               adjust_lapic_timer_advance(vcpu, guest_tsc, tsc_deadline);
+               adjust_lapic_timer_advance(vcpu, 
apic->lapic_timer.advance_expire_delta);
 }
 
 static void start_sw_tscdeadline(struct kvm_lapic *apic)
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index d6d049ba3045..3e72a255543d 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -32,6 +32,7 @@ struct kvm_timer {
        u64 tscdeadline;
        u64 expired_tscdeadline;
        u32 timer_advance_ns;
+       s64 advance_expire_delta;
        atomic_t pending;                       /* accumulated triggered timers 
*/
        bool hv_timer_in_use;
        bool timer_advance_adjust_done;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e7e57de50a3c..35631505421c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8008,6 +8008,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
        ++vcpu->stat.exits;
 
        guest_exit_irqoff();
+       if (lapic_in_kernel(vcpu)) {
+               s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
+               if (delta != S64_MIN) {
+                       trace_kvm_wait_lapic_expire(vcpu->vcpu_id, delta);
+                       vcpu->arch.apic->lapic_timer.advance_expire_delta = 
S64_MIN;
+               }
+       }
 
        local_irq_enable();
        preempt_enable();

so that KVM tracks whether wait_lapic_expire was called, and do not
invoke the tracepoint if not.

Thanks,

Paolo