From: Paolo Bonzini <pbonzini@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>,
Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Cc: kvm <kvm@vger.kernel.org>, Wei Huang <wei@redhat.com>
Subject: Re: IPI broadcast latency in the guest is worse when AVIC is enabled
Date: Tue, 11 Aug 2020 10:28:55 +0200 [thread overview]
Message-ID: <95c26b17-66c6-0050-053b-faa4d63a2347@redhat.com> (raw)
In-Reply-To: <CANRm+Cx597FNRUCyVz1D=B6Vs2GX3Sw57X7Muk+yMpi_hb+v1w@mail.gmail.com>
On 11/08/20 04:04, Wanpeng Li wrote:
> We found that the IPI broadcast latency in the guest when AVIC=1,
> exposing xapic is worse than when AVIC=0, exposing xapic. The host is
> AMD ROME, 2 sockets, 96 cores, 192 threads, the VM is 180 vCPUs. The
> guest boots with kvm-hint-dedicated=on, --overcommit cpu-pm=on, -smp
> 180,sockets=2,cores=45,threads=2, l3-cache=on qemu command-line, the
> pCPU which vCPU is running on is isolated. Both the guest and host
> kernel are 5.8 Linus' tree. (Note, if you fails to boot with
> --overcommit cpu-pm=on, you can comments out commit e72436bc3a52, I
> have a report here, https://lkml.org/lkml/2020/7/8/308)
>
> IPI microbenchmark(https://lkml.org/lkml/2017/12/19/141, Destination
> Shorthand is All excluding self)
>
> avic0_xapic: 12313907508.50 ns
> avic1_xapic: 19106424733.30 ns
> avic0_x2apic: 13073988486.00 ns
I think it depends on the microarchitecture implementation of AVIC?
Paolo
next prev parent reply other threads:[~2020-08-11 8:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-11 2:04 IPI broadcast latency in the guest is worse when AVIC is enabled Wanpeng Li
2020-08-11 8:28 ` Paolo Bonzini [this message]
2020-08-13 7:59 ` Wanpeng Li
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