Re: Multiple CPU support for uvmm on virt-arm64 qemu machine

Hi Philipp,

I'm already using *start_vm()* and setting *cpu* parameter to the values you mentioned, but it is still working randomly (sometimes works and sometimes hangs or one of the VM hangs).

Please find attached my ned script : [image: image.png]

Also I can not understand the effect of the *prio* parameter! I have changed it among different values but nothing changed! What is the effect of the *prio* parameter and when/how can I use it ?

Thanks in advance, Regards

On Thu, Oct 31, 2024 at 8:47 PM Philipp Eppelt < philipp.eppelt@kernkonzept.com> wrote:

Hi Mohamed,

Am 31.10.24 um 14:30 schrieb Mohamed Dawod:

...

Thanks Philipp,

Multiple CPUs worked for virt-arm64 machine

Yippie!

...

I tried to launch 2 linux VMs on top of L4 using uvmm and assign 2 CPUs

to one

...

of the two VMs and another 2 CPUs to the other one. I noticed that the linux booting process becomes slower and as more

CPUs are

...

added to qemu with -smp option and passed to the VMs as more as the VM

booting

...

becomes more slower! Also VMs become working randomly (sometimes they work and sometimes they

hang or

...

one of them hangs) > Why does this strange behaviour happen when using uvmm and 2 Linux VMs ?

To make this easier please show me your ned script starting the VMs.

If you use start_vm() please note that the `cpus` parameter takes a bitmap. So make sure to start VM1 with `cpus=0x3` and VM2 with `cpus=0xc` to place them on separate cores of a four core platform (e.g. QEMU with -smp 4).

Cheers, Philipp

...

Thanks, Regards

On Wed, Oct 30, 2024 at 8:46 PM Philipp Eppelt <

philipp.eppelt@kernkonzept.com

...

mailto:philipp.eppelt@kernkonzept.com> wrote:

Hi Mohamed,

Am 29.10.24 um 10:43 schrieb Mohamed Dawod:
 > Hello,
 > I'm trying to provide multiple CPUs for a linux VM on top of L4.
 > I'm using the qemu virt machine and building for aarch64. so I

used *-smp*

...

 > option to provide more CPUs.
 >
 >     $ qemu-system-aarch64 -M virt,virtualization=true -cpu

cortex-a57

...

-smp 4 -m
 >     1024 -kernel ....etc....
I'm not sure which gic version qemu uses. Please try setting it

explicitly to

...

with gic-version=3 argument:  `-M

virt,virtualization=true,gic-version=3`

...

 >
 > Unfortunately, This didn't work. I tried to add more CPU device

nodes to

...

the dts
 > file *virt-arm_virt-64.dts *but it also didn't work. >
 > I think that it's because of the provided interrupt-controller

with

...

 > *virt-arm_virt-64.dts* in /l4/pkg/uvmm/conf/dts/ which mentioned

that it

...

 > supports only one CPU.
 >
 >     icsoc {
 >              compatible = "simple-bus";
 >              #address-cells = <2>;
 >              #size-cells = <2>;
 >              ranges;
 >
 >              /* Uvmm will adapt the compatible string depending

on the

...

present gic
 >               * version. It expects reg entries that provide

enough space

...

for the
 >               * Cpu/Dist interface for gicv2 (at least 0x1000,

0x1000) or the

...

 >               * Dist/Redist interface for gicv3 (0x10000, 0x20000

...

number of cpus).

I'm not an expert for ARM64, but judging from the line above I'd say

you

...

have to
increase the size of the second reg entry. For example for four

cores:

...

         reg = <0 0x40000 0 0x10000>,
               <0 0x50000 0 0x80000>;

You should be able to just use the github version of this file, it

has a gic

...

node that is configured for 32 cores and comes with four CPU nodes.

https://github.com/kernkonzept/uvmm/blob/master/configs/dts/virt-arm_virt-64... < https://github.com/kernkonzept/uvmm/blob/master/configs/dts/virt-arm_virt-64...

...

 >               * *The entries provided here support any gicv2

setup or a

...

gicv3 setup
 >               * with one Cpu.*
 >               */
 >              gic: interrupt-controller {
 >                  compatible = "arm,gic-400", "arm,cortex-a15-gic",
 >     "arm,cortex-a9-gic";
 >                  #interrupt-cells = <3>;
 >                  #address-cells = <0>;
 >                  interrupt-controller;
 >                  reg = <0 0x40000 0 0x10000>,
 >                        <0 0x50000 0 0x20000>;
 >                  };
 >          };
 >
 >
 > My question now, is there any workaround to support multiple CPUs

for virt

...

 > machine  on arm64  ?

Multiple CPUs should work. For SMP there are a couple of things to

consider:

...

- QEMU: -smp parameter
- Kernel configuration for SMP and the number of maximum cores
- The DTS defines the maximum number of cores for the uvmm will set

up. So

...

adding CPU device nodes is the correct path.
- The ned script defines the number of cores available at runtime to

uvmm. No

...

cpu parameter in the start_vm({}) call means the VM gets access to

all cpus.

...

- Linux must of course also support SMP, but that's very likely not

the problem

...

here ;-)

I hope this sheds some light.

Cheers,
Philipp

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...

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