From: Marcelo Tosatti <mtosatti@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH v3 2/4] KVM: LAPIC: lapic timer interrupt is injected by posted interrupt
Date: Tue, 11 Jun 2019 17:18:52 -0300 [thread overview]
Message-ID: <20190611201849.GA7520@amt.cnet> (raw)
In-Reply-To: <1560255429-7105-3-git-send-email-wanpengli@tencent.com>
On Tue, Jun 11, 2019 at 08:17:07PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Dedicated instances are currently disturbed by unnecessary jitter due
> to the emulated lapic timers fire on the same pCPUs which vCPUs resident.
> There is no hardware virtual timer on Intel for guest like ARM. Both
> programming timer in guest and the emulated timer fires incur vmexits.
> This patch tries to avoid vmexit which is incurred by the emulated
> timer fires in dedicated instance scenario.
>
> When nohz_full is enabled in dedicated instances scenario, the emulated
> timers can be offload to the nearest busy housekeeping cpus since APICv
> is really common in recent years. The guest timer interrupt is injected
> by posted-interrupt which is delivered by housekeeping cpu once the emulated
> timer fires.
>
> ~3% redis performance benefit can be observed on Skylake server.
>
> w/o patch:
>
> VM-EXIT Samples Samples% Time% Min Time Max Time Avg time
>
> EXTERNAL_INTERRUPT 42916 49.43% 39.30% 0.47us 106.09us 0.71us ( +- 1.09% )
>
> w/ patch:
>
> VM-EXIT Samples Samples% Time% Min Time Max Time Avg time
>
> EXTERNAL_INTERRUPT 6871 9.29% 2.96% 0.44us 57.88us 0.72us ( +- 4.02% )
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/lapic.c | 32 +++++++++++++++++++++++++-------
> 1 file changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index e57eeba..020599f 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -133,6 +133,12 @@ inline bool posted_interrupt_inject_timer_enabled(struct kvm_vcpu *vcpu)
> }
> EXPORT_SYMBOL_GPL(posted_interrupt_inject_timer_enabled);
>
> +static inline bool can_posted_interrupt_inject_timer(struct kvm_vcpu *vcpu)
> +{
> + return posted_interrupt_inject_timer_enabled(vcpu) &&
> + kvm_hlt_in_guest(vcpu->kvm);
> +}
Hi Li,
Don't think its necessary to depend on kvm_hlt_in_guest: Can also use
exitless injection if the guest is running (think DPDK style workloads
that busy-spin on network card).
next prev parent reply other threads:[~2019-06-11 20:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-11 12:17 [PATCH v3 0/4] KVM: LAPIC: Implement Exitless Timer Wanpeng Li
2019-06-11 12:17 ` [PATCH v3 1/4] KVM: LAPIC: Make lapic timer unpinned when timer is injected by pi Wanpeng Li
2019-06-11 20:39 ` Marcelo Tosatti
2019-06-12 0:45 ` Wanpeng Li
2019-06-12 16:15 ` Marcelo Tosatti
2019-06-11 12:17 ` [PATCH v3 2/4] KVM: LAPIC: lapic timer interrupt is injected by posted interrupt Wanpeng Li
2019-06-11 20:18 ` Marcelo Tosatti [this message]
2019-06-12 1:48 ` Wanpeng Li
2019-06-12 15:22 ` Radim Krčmář
2019-06-12 21:51 ` Marcelo Tosatti
2019-06-11 12:17 ` [PATCH v3 3/4] KVM: LAPIC: Ignore timer migration when lapic timer is injected by posted-interrupt Wanpeng Li
2019-06-11 12:17 ` [PATCH v3 4/4] KVM: LAPIC: add advance timer support to pi_inject_timer Wanpeng Li
2019-06-13 7:59 ` [PATCH v3 0/4] KVM: LAPIC: Implement Exitless Timer Maxim Levitsky
2019-06-13 8:25 ` Wanpeng Li
2019-06-13 9:49 ` Maxim Levitsky
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