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 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
