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: <CANRm+CyATAvi3-u6bzpUXWCWARzf1xHxJ62+GPncBcCnbJAFMA@mail.gmail.com>
Date:   Fri, 14 Oct 2016 18:05:59 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        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

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 :)

Regards,
Wanpeng Li