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

From: Paolo Bonzini
Date: Mon May 20 2019 - 07:43:49 EST


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