linux-kernel - Re: [PATCH v3 0/5] KVM: LAPIC: Optimize timer latency further

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Message-ID: <CANRm+CxR_jrB=tMpmM9OMEJ-pm8gdfMNN7UsDdQ+YrG_akGdAg@mail.gmail.com>
Date:   Wed, 12 Jun 2019 17:40:57 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v3 0/5] KVM: LAPIC: Optimize timer latency further

Sorry, send out the wrong patchset, please ignore.
On Wed, 12 Jun 2019 at 17:36, Wanpeng Li <kernellwp@...il.com> wrote:
>
> Advance lapic timer tries to hidden the hypervisor overhead between the
> host emulated timer fires and the guest awares the timer is fired. However,
> it just hidden the time between apic_timer_fn/handle_preemption_timer ->
> wait_lapic_expire, instead of the real position of vmentry which is
> mentioned in the orignial commit d0659d946be0 ("KVM: x86: add option to
> advance tscdeadline hrtimer expiration"). There is 700+ cpu cycles between
> the end of wait_lapic_expire and before world switch on my haswell desktop.
>
> This patchset tries to narrow the last gap(wait_lapic_expire -> world switch),
> it takes the real overhead time between apic_timer_fn/handle_preemption_timer
> and before world switch into consideration when adaptively tuning timer
> advancement. The patchset can reduce 40% latency (~1600+ cycles to ~1000+
> cycles on a haswell desktop) for kvm-unit-tests/tscdeadline_latency when
> testing busy waits.
>
> v2 -> v3:
>  * expose 'kvm_timer.timer_advance_ns' to userspace
>  * move the tracepoint below guest_exit_irqoff()
>  * move wait_lapic_expire() before flushing the L1
>
> v1 -> v2:
>  * fix indent in patch 1/4
>  * remove the wait_lapic_expire() tracepoint and expose by debugfs
>  * move the call to wait_lapic_expire() into vmx.c and svm.c
>
> Wanpeng Li (5):
>   KVM: LAPIC: Extract adaptive tune timer advancement logic
>   KVM: LAPIC: Fix lapic_timer_advance_ns parameter overflow
>   KVM: LAPIC: Expose per-vCPU timer_advance_ns to userspace
>   KVM: LAPIC: Delay trace advance expire delta
>   KVM: LAPIC: Optimize timer latency further
>
>  arch/x86/kvm/debugfs.c | 16 +++++++++++++
>  arch/x86/kvm/lapic.c   | 62 +++++++++++++++++++++++++++++---------------------
>  arch/x86/kvm/lapic.h   |  3 ++-
>  arch/x86/kvm/svm.c     |  4 ++++
>  arch/x86/kvm/vmx/vmx.c |  4 ++++
>  arch/x86/kvm/x86.c     |  7 +++---
>  6 files changed, 65 insertions(+), 31 deletions(-)
>
> --
> 2.7.4
>