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

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Message-ID: <9d7fffc9-7e46-fa03-70bf-e803c2d61786@redhat.com>
Date:   Fri, 14 Oct 2016 13:11:58 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Yunhong Jiang <yunhong.jiang@...el.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH RFC V3 0/6] KVM: LAPIC: Add APIC Timer periodic/oneshot
 mode VMX preemption timer support



On 14/10/2016 12:05, Wanpeng Li wrote:
> 2016-10-13 19:34 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> [...]
>>
>> 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