Re: [PATCH] KVM: LAPIC: Reset timer_advance_ns if timer mode switch

Vitaly Kuznetsov
2020-08-31T12:48:26Z

Wanpeng Li <kernellwp@gmail.com> writes:

> From: Wanpeng Li <wanpengli@tencent.com>
>
> per-vCPU timer_advance_ns should be set to 0 if timer mode is not tscdeadline
> otherwise we waste cpu cycles in the function lapic_timer_int_injected(),

lapic_timer_int_injected is just a test, kvm_wait_lapic_expire()
(__kvm_wait_lapic_expire()) maybe?

> especially on AMD platform which doesn't support tscdeadline mode. We can
> reset timer_advance_ns to the initial value if switch back to
> tscdealine

'tscdeadline'

> timer mode.
>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/lapic.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 654649b..abc296d 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1499,10 +1499,16 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
> kvm_lapic_set_reg(apic, APIC_TMICT, 0);
> apic->lapic_timer.period = 0;
> apic->lapic_timer.tscdeadline = 0;
> + if (timer_mode == APIC_LVT_TIMER_TSCDEADLINE &&
> + lapic_timer_advance_dynamic)
> + apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_NS_INIT;
> }
> apic->lapic_timer.timer_mode = timer_mode;
> limit_periodic_timer_frequency(apic);
> }
> + if (timer_mode != APIC_LVT_TIMER_TSCDEADLINE &&
> + lapic_timer_advance_dynamic)
> + apic->lapic_timer.timer_advance_ns = 0;
> }
>
> /*

--
Vitaly