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?

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

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

On Mon, 13 Dec 2021 16:06:14 +0000, Peter Maydell <peter.maydell(a)linaro.org&gt; wrote: > > KVM on big.little setups is a kernel-level question really; I've > cc'd the kvmarm list. Thanks Peter for throwing us under the big-little bus! ;-) > > On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; 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. s/A55/A53/. There were thankfully no A72+A55 ever produced (just the though of it makes me sick). >>>> >>>> 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. Disclaimer: I know nothing about libvirt (and no, I don't want to know! ;-). However, for things to be reliable, you need to taskset the whole QEMU process to the CPU type you intend to use.

That's because, AFAICT, QEMU will snapshot the system registers outside of the vcpu threads, and attempt to use the result to configure the actual vcpu threads. If they happen to run on different CPU types, the sysregs will differ in incompatible ways and an error will be returned. This may or may not be a bug, I don't know (I see it as a feature).

If you are annoyed with this behaviour, you can always use a different VMM that won't care about such difference (crosvm or kvmtool, to name a few).

However, the guest will be able to observe the migration from one cpu type to another. This may or may not affect your guest's behaviour.

I personally find the QEMU behaviour reasonable. KVM/arm64 make little effort to support BL virtualisation as design choice (I value my sanity), and userspace is still in control of the placement. >>>> 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. Vote with your money. If you too think that BL systems are utter crap, do not buy them! Or treat them as 'two systems in one', which is what I do. From that angle, this is of great value! ;-)

>>>> I guess with projects like Asahi Linux making progress, there will be >>>> more and more such problems. Well, not more than any other big-little system. They suffer from similar issues, plus those resulting from not fully implementing the ARM architecture. They are however more consistent in their feature set than the ARM implementations ever were. >>>> >>>> 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. No. They are all notionally running. It is the scheduler that places tasks (such as a vcpu) on a 'convenient' core, where 'convenient' depends on the scheduling policy. HTH, M.

On 12/14/21 01:41, Qu Wenruo wrote: > > > On 2021/12/14 00:49, Marc Zyngier wrote: >> On Mon, 13 Dec 2021 16:06:14 +0000, >> Peter Maydell <peter.maydell(a)linaro.org&gt; wrote: >>> >>> KVM on big.little setups is a kernel-level question really; I've >>> cc'd the kvmarm list. >> >> Thanks Peter for throwing us under the big-little bus! ;-) >> >>> >>> On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; 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. >> >> s/A55/A53/. There were thankfully no A72+A55 ever produced (just the >> though of it makes me sick). >> >>>>>> >>>>>> 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. >> >> Disclaimer: I know nothing about libvirt (and no, I don't want to >> know! ;-). >> >> However, for things to be reliable, you need to taskset the whole QEMU >> process to the CPU type you intend to use. > > Yep, that's what I'm doing. > >> That's because, AFAICT, >> QEMU will snapshot the system registers outside of the vcpu threads, >> and attempt to use the result to configure the actual vcpu threads. If >> they happen to run on different CPU types, the sysregs will differ in >> incompatible ways and an error will be returned. This may or may not >> be a bug, I don't know (I see it as a feature). > > Then this brings another question. > > If we can pin each vCPU to each physical core (both little and big), > then as long as the registers are per-vCPU based, it should be able to > pass both big and little cores to the VM. > > Yeah, I totally understand this screw up the scheduling, but that's at > least what (some insane) users want (just like me). > >> >> If you are annoyed with this behaviour, you can always use a different >> VMM that won't care about such difference (crosvm or kvmtool, to name >> a few). > > Sounds pretty interesting, a new world but without libvirt... > >> However, the guest will be able to observe the migration from >> one cpu type to another. This may or may not affect your guest's >> behaviour. > > Not sure if it's possible to pin each vCPU thread to each core, but let > me try. > Sure it is, for instance: <cputune> <vcpupin vcpu="0" cpuset="1-4,^2"/> <vcpupin vcpu="1" cpuset="0,1"/> <vcpupin vcpu="2" cpuset="2,3"/> <vcpupin vcpu="3" cpuset="0,4"/> <emulatorpin cpuset="1-3"/> <iothreadpin iothread="1" cpuset="5,6"/> <iothreadpin iothread="2" cpuset="7,8"/> </cputune>

pins vCPU#0 onto host CPUs 1-4, excluding 2; vCPU#1 onto host CPUs 0-1 and so on. You can also pin emulator (QEMU) and its iothreads. It's documented here: https://libvirt.org/formatdomain.html#cpu-tuning Michal

You are still missing the point of how QEMU works: - QEMU creates a dummy VM with a single vcpu. This can happen on *any* CPU. - It snapshots the sysregs for this vcpu, and keep them for later - It then destroy this VM - QEMU then creates the full VM, with all the vcpus - Each vcpu gets initialised with the state saved earlier. If any vcpu is initialised on a physical CPU of a different type from the one that has been used for the dummy VM, you lose, as we cannot restore some of the registers such as MIDR_EL1 (and other registers that KVM considers as invariant).

The best workaround is to taskset the QEMU process (and I really mean the process, not individual threads) to an homogeneous set of CPUs and be done with it.

On Tue, 14 Dec 2021 08:16:40 +0000, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; wrote: > > > > On 2021/12/14 15:53, Michal Prívozník wrote: >> On 12/14/21 01:41, Qu Wenruo wrote: >>> >>> >>> On 2021/12/14 00:49, Marc Zyngier wrote: >>>> On Mon, 13 Dec 2021 16:06:14 +0000, >>>> Peter Maydell <peter.maydell(a)linaro.org&gt; wrote: >>>>> >>>>> KVM on big.little setups is a kernel-level question really; I've >>>>> cc'd the kvmarm list. >>>> >>>> Thanks Peter for throwing us under the big-little bus! ;-) >>>> >>>>> >>>>> On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; 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. >>>> >>>> s/A55/A53/. There were thankfully no A72+A55 ever produced (just the >>>> though of it makes me sick). >>>> >>>>>>>> >>>>>>>> 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. >>>> >>>> Disclaimer: I know nothing about libvirt (and no, I don't want to >>>> know! ;-). >>>> >>>> However, for things to be reliable, you need to taskset the whole QEMU >>>> process to the CPU type you intend to use. >>> >>> Yep, that's what I'm doing. >>> >>>> That's because, AFAICT, >>>> QEMU will snapshot the system registers outside of the vcpu threads, >>>> and attempt to use the result to configure the actual vcpu threads. If >>>> they happen to run on different CPU types, the sysregs will differ in >>>> incompatible ways and an error will be returned. This may or may not >>>> be a bug, I don't know (I see it as a feature). >>> >>> Then this brings another question. >>> >>> If we can pin each vCPU to each physical core (both little and big), >>> then as long as the registers are per-vCPU based, it should be able to >>> pass both big and little cores to the VM. >>> >>> Yeah, I totally understand this screw up the scheduling, but that's at >>> least what (some insane) users want (just like me). >>> >>>> >>>> If you are annoyed with this behaviour, you can always use a different >>>> VMM that won't care about such difference (crosvm or kvmtool, to name >>>> a few). >>> >>> Sounds pretty interesting, a new world but without libvirt... >>> >>>> However, the guest will be able to observe the migration from >>>> one cpu type to another. This may or may not affect your guest's >>>> behaviour. >>> >>> Not sure if it's possible to pin each vCPU thread to each core, but let >>> me try. >>> >> >> Sure it is, for instance: >> >> <cputune> >> <vcpupin vcpu="0" cpuset="1-4,^2"/> >> <vcpupin vcpu="1" cpuset="0,1"/> >> <vcpupin vcpu="2" cpuset="2,3"/> >> <vcpupin vcpu="3" cpuset="0,4"/> >> <emulatorpin cpuset="1-3"/> >> <iothreadpin iothread="1" cpuset="5,6"/> >> <iothreadpin iothread="2" cpuset="7,8"/> >> </cputune> > > That's what I have already tried before. > I pinned vcpu 0-6 to physical core 0-6, and still no reliable boot up. > > And that's why I'm asking here. You are still missing the point of how QEMU works: - QEMU creates a dummy VM with a single vcpu. This can happen on *any* CPU.

- It snapshots the sysregs for this vcpu, and keep them for later - It then destroy this VM - QEMU then creates the full VM, with all the vcpus - Each vcpu gets initialised with the state saved earlier. If any vcpu is initialised on a physical CPU of a different type from the one that has been used for the dummy VM, you lose, as we cannot restore some of the registers such as MIDR_EL1 (and other registers that KVM considers as invariant). To fix this, you need to change QEMU's notion of a template VM, or change KVM's notion of invariant registers. The former is quite hard, and the later breaks a ton of things for guests, such as errata workarounds.

The best workaround is to taskset the QEMU process (and I really mean the process, not individual threads) to an homogeneous set of CPUs and be done with it.

M.

On 2021/12/14 00:49, Marc Zyngier wrote: > On Mon, 13 Dec 2021 16:06:14 +0000, > Peter Maydell <peter.maydell(a)linaro.org&gt; wrote: >> >> KVM on big.little setups is a kernel-level question really; I've >> cc'd the kvmarm list. > > Thanks Peter for throwing us under the big-little bus! ;-) > >> >> On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; 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. > > s/A55/A53/. There were thankfully no A72+A55 ever produced (just the > though of it makes me sick). > >>>>> >>>>> 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. > > Disclaimer: I know nothing about libvirt (and no, I don't want to > know! ;-). > > However, for things to be reliable, you need to taskset the whole QEMU > process to the CPU type you intend to use. Yep, that's what I'm doing.

> That's because, AFAICT, > QEMU will snapshot the system registers outside of the vcpu threads, > and attempt to use the result to configure the actual vcpu threads. If > they happen to run on different CPU types, the sysregs will differ in > incompatible ways and an error will be returned. This may or may not > be a bug, I don't know (I see it as a feature). Then this brings another question. If we can pin each vCPU to each physical core (both little and big), then as long as the registers are per-vCPU based, it should be able to pass both big and little cores to the VM.

Yeah, I totally understand this screw up the scheduling, but that's at least what (some insane) users want (just like me).

> > If you are annoyed with this behaviour, you can always use a different > VMM that won't care about such difference (crosvm or kvmtool, to name > a few). Sounds pretty interesting, a new world but without libvirt... > However, the guest will be able to observe the migration from > one cpu type to another. This may or may not affect your guest's > behaviour. Not sure if it's possible to pin each vCPU thread to each core, but let me try.

> I personally find the QEMU behaviour reasonable. KVM/arm64 make little > effort to support BL virtualisation as design choice (I value my > sanity), and userspace is still in control of the placement. > >>>>> 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. > > Vote with your money. If you too think that BL systems are utter crap, > do not buy them! Or treat them as 'two systems in one', which is what > I do. From that angle, this is of great value! ;-) I guess I'm setting my expectation too high for rk3399, just seeing its multi-thread perf beating RPI4 and has better IO doesn't mean it's a perfect fit for VM.

On Tue, Dec 14, 2021 at 09:34:18AM +0000, Marc Zyngier wrote: > On Tue, 14 Dec 2021 00:41:01 +0000, > Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; wrote: >> >> >> >> On 2021/12/14 00:49, Marc Zyngier wrote: >>> On Mon, 13 Dec 2021 16:06:14 +0000, >>> Peter Maydell <peter.maydell(a)linaro.org&gt; wrote: >>>> >>>> KVM on big.little setups is a kernel-level question really; I've >>>> cc'd the kvmarm list. >>> >>> Thanks Peter for throwing us under the big-little bus! ;-) >>> >>>> >>>> On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; 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. >>> >>> s/A55/A53/. There were thankfully no A72+A55 ever produced (just the >>> though of it makes me sick). >>> >>>>>>> >>>>>>> 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. >>> >>> Disclaimer: I know nothing about libvirt (and no, I don't want to >>> know! ;-). >>> >>> However, for things to be reliable, you need to taskset the whole QEMU >>> process to the CPU type you intend to use. >> >> Yep, that's what I'm doing. > > Are you sure? The xml directive above seem to only apply to the vcpus, > and no other QEMU thread. For historical reasons this XML element is a bit misleadingly named. With the config <vcpu placement='static' cpuset='4-5'>2</vcpu> the 'cpuset' applies to the QEMU process as a whole - its vCPUs, I/O threads and any other emulator threads. There is a separate config for setting per-VCPU binding which was illustrated elsewhere in this thread.

Regards, Daniel

On Mon, 13 Dec 2021 16:06:14 +0000, Peter Maydell <peter.maydell(a)linaro.org&gt; wrote: > > KVM on big.little setups is a kernel-level question really; I've > cc'd the kvmarm list. Thanks Peter for throwing us under the big-little bus! ;-) > > On Mon, 13 Dec 2021 at 15:02, Qu Wenruo <quwenruo.btrfs(a)gmx.com&gt; 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. s/A55/A53/. There were thankfully no A72+A55 ever produced (just the though of it makes me sick). >>>> >>>> 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. Disclaimer: I know nothing about libvirt (and no, I don't want to know! ;-). However, for things to be reliable, you need to taskset the whole QEMU process to the CPU type you intend to use. That's because, AFAICT, QEMU will snapshot the system registers outside of the vcpu threads, and attempt to use the result to configure the actual vcpu threads. If they happen to run on different CPU types, the sysregs will differ in incompatible ways and an error will be returned. This may or may not be a bug, I don't know (I see it as a feature).