From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 3/3] KVM: LAPIC: Optimize PMI delivering overhead
Date: Fri, 08 Oct 2021 12:52:46 +0200 [thread overview]
Message-ID: <87ily73i0x.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <1633687054-18865-3-git-send-email-wanpengli@tencent.com>
Wanpeng Li <kernellwp@gmail.com> writes:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> The overhead of kvm_vcpu_kick() is huge since expensive rcu/memory
> barrier etc operations in rcuwait_wake_up(). It is worse when local
> delivery since the vCPU is scheduled and we still suffer from this.
> We can observe 12us+ for kvm_vcpu_kick() in kvm_pmu_deliver_pmi()
> path by ftrace before the patch and 6us+ after the optimization.
>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/lapic.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 76fb00921203..ec6997187c6d 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1120,7 +1120,8 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
> case APIC_DM_NMI:
> result = 1;
> kvm_inject_nmi(vcpu);
> - kvm_vcpu_kick(vcpu);
> + if (vcpu != kvm_get_running_vcpu())
> + kvm_vcpu_kick(vcpu);
Out of curiosity,
can this be converted into a generic optimization for kvm_vcpu_kick()
instead? I.e. if kvm_vcpu_kick() is called for the currently running
vCPU, there's almost nothing to do, especially when we already have a
request pending, right? (I didn't put too much though to it)
> break;
>
> case APIC_DM_INIT:
--
Vitaly
next prev parent reply other threads:[~2021-10-08 10:52 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 9:57 [PATCH 1/3] KVM: emulate: #GP when emulating rdpmc if CR0.PE is 1 Wanpeng Li
2021-10-08 9:57 ` [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 Wanpeng Li
2021-10-08 11:02 ` Like Xu
2021-10-08 11:17 ` Wanpeng Li
2021-10-08 9:57 ` [PATCH 3/3] KVM: LAPIC: Optimize PMI delivering overhead Wanpeng Li
2021-10-08 10:52 ` Vitaly Kuznetsov [this message]
2021-10-08 11:06 ` Wanpeng Li
2021-10-08 15:59 ` Sean Christopherson
2021-10-09 9:14 ` Wanpeng Li
2021-10-08 15:20 ` [PATCH 1/3] KVM: emulate: #GP when emulating rdpmc if CR0.PE is 1 Sean Christopherson
2021-10-09 9:09 ` Wanpeng Li
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87ily73i0x.fsf@vitty.brq.redhat.com \
--to=vkuznets@redhat.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kernellwp@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).