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From: Wanpeng Li <kernellwp@gmail.com>
To: LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH v4 0/5] KVM: LAPIC: Optimize timer latency further
Date: Wed, 22 May 2019 16:51:52 +0800	[thread overview]
Message-ID: <CANRm+Cx0o14p_pTp5_dk5-W=mL20E9DHAFK-qYYNNv+5VuSR=Q@mail.gmail.com> (raw)
In-Reply-To: <1558340289-6857-1-git-send-email-wanpengli@tencent.com>

On Mon, 20 May 2019 at 16:18, Wanpeng Li <kernellwp@gmail.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.

Testing on a Skylake Server, w/ nohz=off, idle=poll in the guest.
Reduces average cyclictest latency from 3us to 2us.

Regards,
Wanpeng Li

      parent reply	other threads:[~2019-05-22  8:52 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20  8:18 Wanpeng Li
2019-05-20  8:18 ` [PATCH v4 1/5] KVM: LAPIC: Extract adaptive tune timer advancement logic Wanpeng Li
2019-05-20  8:18 ` [PATCH v4 2/5] KVM: LAPIC: Fix lapic_timer_advance_ns parameter overflow Wanpeng Li
2019-05-20  8:18 ` [PATCH v4 3/5] KVM: LAPIC: Expose per-vCPU timer_advance_ns to userspace Wanpeng Li
2019-05-20  8:18 ` [PATCH v4 4/5] KVM: LAPIC: Delay trace advance expire delta Wanpeng Li
2019-05-20 11:14   ` Paolo Bonzini
2019-05-20 11:22     ` Wanpeng Li
2019-05-20 11:33       ` Paolo Bonzini
2019-05-20 11:36         ` Wanpeng Li
2019-05-20 11:41           ` Paolo Bonzini
2019-05-20 11:45             ` Wanpeng Li
2019-05-20  8:18 ` [PATCH v4 5/5] KVM: LAPIC: Optimize timer latency further Wanpeng Li
2019-05-20 11:16 ` [PATCH v4 0/5] " Paolo Bonzini
2019-05-22  8:51 ` Wanpeng Li [this message]

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