Re: Libvirt on little.BIG ARM systems unable to start guest if no cpuset is provided

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



KVM on big.little setups is a kernel-level question really; I've
cc'd the kvmarm list.

On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs@xxxxxxx> wrote:
>
>
>
> On 2021/12/13 21:17, Michal Prívozník wrote:
> > On 12/11/21 02:58, Qu Wenruo wrote:
> >> Hi,
> >>
> >> Recently I got my libvirt setup on both RK3399 (RockPro64) and RPI CM4,
> >> with upstream kernels.
> >>
> >> For RPI CM4 its mostly smooth sail, but on RK3399 due to its little.BIG
> >> setup (core 0-3 are 4x A55 cores, and core 4-5 are 2x A72 cores), it
> >> brings quite some troubles for VMs.
> >>
> >> In short, without proper cpuset to bind the VM to either all A72 cores
> >> or all A55 cores, the VM will mostly fail to boot.
> >>
> >> Currently the working xml is:
> >>
> >>    <vcpu placement='static' cpuset='4-5'>2</vcpu>
> >>    <cpu mode='host-passthrough' check='none'/>
> >>
> >> But even with vcpupin, pinning each vcpu to each physical core, VM will
> >> mostly fail to start up due to vcpu initialization failed with -EINVAL.
> >>
> >>
> >> This brings a problem, in theory RK3399 SoC should out-perform BCM2711
> >> in multi-core performance, but if a VM can only be bind to either A72 or
> >> A55 cores, then the performance is no longer competitive against
> >> BCM2711, wasting the PCIE 2.0 x4 capacity.
> >>
> >> I guess with projects like Asahi Linux making progress, there will be
> >> more and more such problems.
> >>
> >> Any clue on how to properly pass all physical CPU cores to VM for
> >> little.BIG setup?
> >>
> >
> > I have never met big.LITTLE but my understanding was that those big
> > cores are compatible with little ones and the only difference is that
> > the big ones are shut off if there's no demand (to save energy) leaving
> > only the little ones running.
>
> The big ones are not disabled AFAIK.
>
> And even changing the CPU model to A53 (the little ones), it still fails
> to boot, thus it looks like A72 is not really able to emulate A53 cores?
>
> >
> > Anyway, this is likely too high level forum and I'd ask QEMU developers:
> >
> > https://www.qemu.org/support/
>
> That's indeed the case, adding qemu to the CC list.
>
> And I found an existing bug report:
> https://bugs.linaro.org/show_bug.cgi?id=1443

(This bug tracking system was essentially abandoned years ago; the
status of leftover bugs within it isn't indicative of anything.)

> But I still didn't get the point why the 1:1 CPU-to-vcpu mapping still
> doesn't work.

-- PMM





[Index of Archives]     [Virt Tools]     [Lib OS Info]     [Fedora Users]     [Fedora Desktop]     [Fedora SELinux]     [Yosemite News]     [KDE Users]

  Powered by Linux