On Mon, 20 May 2019 at 19:14, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 20/05/19 10:18, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> >
> > wait_lapic_expire() call was moved above guest_enter_irqoff() because of
> > its tracepoint, which violated the RCU extended quiescent state invoked
> > by guest_enter_irqoff()[1][2]. This patch simply moves the tracepoint
> > below guest_exit_irqoff() in vcpu_enter_guest(). Snapshot the delta before
> > VM-Enter, but trace it after VM-Exit. This can help us to move
> > wait_lapic_expire() just before vmentry in the later patch.
> >
> > [1] Commit 8b89fe1f6c43 ("kvm: x86: move tracepoints outside extended quiescent state")
> > [2] https://patchwork.kernel.org/patch/7821111/
>
> This is a bit confusing, since the delta is printed after the
> corresponding vmexit but the wait is done before the vmentry. I think
> we can drop the tracepoint:
>
> ------------- 8< ----------------
> From ae148d98d49b96b5222e2c78ac1b1e13cc526d71 Mon Sep 17 00:00:00 2001
> From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Date: Mon, 20 May 2019 13:10:01 +0200
> Subject: [PATCH] KVM: lapic: replace wait_lapic_expire tracepoint with
> restart_apic_timer
>
> wait_lapic_expire() call was moved above guest_enter_irqoff() because of
> its tracepoint, which violated the RCU extended quiescent state invoked
> by guest_enter_irqoff()[1][2].
>
> We would like to move wait_lapic_expire() just before vmentry, which would
> place wait_lapic_expire() again inside the extended quiescent state. Drop
> the tracepoint, but add instead another one that can be useful and where
> we can check the status of the adaptive tuning procedure.
https://lkml.org/lkml/2019/5/15/1435
Maybe Sean's comment is reasonable, per-vCPU debugfs entry for
adaptive tuning and wait_lapic_expire() tracepoint for hand tuning.
Regards,
Wanpeng Li
>
> [1] Commit 8b89fe1f6c43 ("kvm: x86: move tracepoints outside extended quiescent state")
> [2] https://patchwork.kernel.org/patch/7821111/
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> ---
> arch/x86/kvm/lapic.c | 4 +++-
> arch/x86/kvm/trace.h | 15 +++++++--------
> 2 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index c12b090f4fad..8f05c1d0b486 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1545,7 +1545,6 @@ 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);
>
> if (guest_tsc < tsc_deadline)
> __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
> @@ -1763,6 +1762,9 @@ static void start_sw_timer(struct kvm_lapic *apic)
>
> static void restart_apic_timer(struct kvm_lapic *apic)
> {
> + trace_kvm_restart_apic_timer(apic->vcpu->vcpu_id,
> + apic->lapic_timer.timer_advance_ns);
> +
> preempt_disable();
>
> if (!apic_lvtt_period(apic) && atomic_read(&apic->lapic_timer.pending))
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index 4d47a2631d1f..f6e000038f3f 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -953,24 +953,23 @@
> __entry->flags)
> );
>
> -TRACE_EVENT(kvm_wait_lapic_expire,
> - TP_PROTO(unsigned int vcpu_id, s64 delta),
> - TP_ARGS(vcpu_id, delta),
> +TRACE_EVENT(kvm_restart_apic_timer,
> + TP_PROTO(unsigned int vcpu_id, u32 advance),
> + TP_ARGS(vcpu_id, advance),
>
> TP_STRUCT__entry(
> __field( unsigned int, vcpu_id )
> - __field( s64, delta )
> + __field( u32, advance )
> ),
>
> TP_fast_assign(
> __entry->vcpu_id = vcpu_id;
> - __entry->delta = delta;
> + __entry->advance = advance;
> ),
>
> - TP_printk("vcpu %u: delta %lld (%s)",
> + TP_printk("vcpu %u: advance %u",
> __entry->vcpu_id,
> - __entry->delta,
> - __entry->delta < 0 ? "early" : "late")
> + __entry->advance)
> );
>
> TRACE_EVENT(kvm_enter_smm,
