Re: [PATCH RFC V3 0/6] KVM: LAPIC: Add APIC Timer periodic/oneshot mode VMX preemption timer support

[Paolo Bonzini]

On 14/10/2016 12:05, Wanpeng Li wrote:
> 2016-10-13 19:34 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>:
> [...]
>>
>> The patchset reduces ~300+ clock cycles for each APIC timer oneshot mode
>> operation virtualization. However, the performance of periodic mode is
>> still bad, so this version is still a RFC. Your comments to improve the
>> patchset is a great appreciated.
> 
> I observed that the clock cycles between the start of
> kvm_lapic_expired_hv_timer() (periodic mode emulated through restart a
> preemption timer after the last preemption timer vmexit) to
> kvm_inject_apic_timer_irqs() is almost half of the clock cycles
> between the start of apic_timer_fn() (periodic mode emulated through
> hrtimer) to kvm_inject_apic_timers_irqs(), so the overhead of
> preemption timer is lower in this path. Maybe something is still not
> correct in other places which results in performance of periodic mode
> emulated by VMX preemption timer is still not good. Any help is a
> great appreciated. :)
> 
> Radim, Paolo, ping :)

Just post the patches and we'll see. :)  Another useful thing to do is
to prepare testcases similar to tscdeadline_latency, but using the
periodic and oneshot modes.

Paolo