Re: [RFC PATCH 2/5] hw/arm/virt: Add cpu-map to device tree

[Ying Fang]

On 2/25/2021 7:16 PM, Andrew Jones wrote:
> Hi Ying Fang,
>
> The only difference between this and what I have in my tree[*]
> is the removal of the socket node (which has been in the Linux
> docs since June 2019). Any reason why you removed that node? In
> any case, I think I deserve a bit more credit for this patch.

Sorry, you surely deserve it. I forget to add it here.
Should I have a SOB of you here ?

The latest linux kernel use a four level cpu topology defined in

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/cpu/cpu-topology.txt?h=v5.11

ie. socket node, cluster node, core node, thread node.

The linux kernel 4.19 LTS use a three level cpu topology defined in
Documentation/devicetree/bindings/arm/topology.txt

ie. cluster node, core node, thread node.

Currently Qemu x86 has 4 level of cpu topology as: socket, die, core,
thread. Should arm64 active like it here ?

Further more, latest linux kernel define the cpu topology struct as.
So maybe it only cares about the socket, core, thread topology levels.

struct cpu_topology { 

    int thread_id; 

    int core_id; 

    int package_id; 

    int llc_id; 

    cpumask_t thread_sibling; 

    cpumask_t core_sibling; 

    cpumask_t llc_sibling; 

};

> [*] 
> https://github.com/rhdrjones/qemu/commit/35feecdd43475608c8f55973a0c159eac4aafefd
>
> Thanks,
> drew
>
> On Thu, Feb 25, 2021 at 04:56:24PM +0800, Ying Fang wrote:
> > Support device tree CPU topology descriptions.
> >
> > Signed-off-by: Ying Fang <fangying1@huawei.com>
> > ---
> >   hw/arm/virt.c         | 38 +++++++++++++++++++++++++++++++++++++-
> >   include/hw/arm/virt.h |  1 +
> >   2 files changed, 38 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 371147f3ae..c133b342b8 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -351,10 +351,11 @@ static void fdt_add_cpu_nodes(const VirtMachineState *vms)
> >       int cpu;
> >       int addr_cells = 1;
> >       const MachineState *ms = MACHINE(vms);
> > +    const VirtMachineClass *vmc = VIRT_MACHINE_GET_CLASS(vms);
> >       int smp_cpus = ms->smp.cpus;
> >   
> >       /*
> > -     * From Documentation/devicetree/bindings/arm/cpus.txt
> > +     * See Linux Documentation/devicetree/bindings/arm/cpus.yaml
> >        *  On ARM v8 64-bit systems value should be set to 2,
> >        *  that corresponds to the MPIDR_EL1 register size.
> >        *  If MPIDR_EL1[63:32] value is equal to 0 on all CPUs
> > @@ -407,8 +408,42 @@ static void fdt_add_cpu_nodes(const VirtMachineState *vms)
> >                   ms->possible_cpus->cpus[cs->cpu_index].props.node_id);
> >           }
> >   
> > +        if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
> > +            qemu_fdt_setprop_cell(vms->fdt, nodename, "phandle",
> > +                                  qemu_fdt_alloc_phandle(vms->fdt));
> > +        }
> > +
> >           g_free(nodename);
> >       }
> > +
> > +    if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
> > +        /*
> > +         * See Linux Documentation/devicetree/bindings/cpu/cpu-topology.txt
> > +         */
> > +        qemu_fdt_add_subnode(vms->fdt, "/cpus/cpu-map");
> > +
> > +        for (cpu = ms->smp.cpus - 1; cpu >= 0; cpu--) {
> > +            char *cpu_path = g_strdup_printf("/cpus/cpu@%d", cpu);
> > +            char *map_path;
> > +
> > +            if (ms->smp.threads > 1) {
> > +                map_path = g_strdup_printf(
> > +                            "/cpus/cpu-map/%s%d/%s%d/%s%d",
> > +                            "cluster", cpu / (ms->smp.cores * ms->smp.threads),

a cluster node may be replaced by socket to keep accord with the latest 
kernel.

> > +                            "core", (cpu / ms->smp.threads) % ms->smp.cores,
> > +                            "thread", cpu % ms->smp.threads);
> > +            } else {
> > +                map_path = g_strdup_printf(
> > +                            "/cpus/cpu-map/%s%d/%s%d",
> > +                            "cluster", cpu / ms->smp.cores,
> > +                            "core", cpu % ms->smp.cores);
> > +            }
> > +            qemu_fdt_add_path(vms->fdt, map_path);
> > +            qemu_fdt_setprop_phandle(vms->fdt, map_path, "cpu", cpu_path);
> > +            g_free(map_path);
> > +            g_free(cpu_path);
> > +        }
> > +    }
> >   }
> >   
> >   static void fdt_add_its_gic_node(VirtMachineState *vms)
> > @@ -2742,6 +2777,7 @@ static void virt_machine_5_2_options(MachineClass *mc)
> >       virt_machine_6_0_options(mc);
> >       compat_props_add(mc->compat_props, hw_compat_5_2, hw_compat_5_2_len);
> >       vmc->no_secure_gpio = true;
> > +    vmc->no_cpu_topology = true;
> >   }
> >   DEFINE_VIRT_MACHINE(5, 2)
> >   
> > diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> > index ee9a93101e..7ef6d08ac3 100644
> > --- a/include/hw/arm/virt.h
> > +++ b/include/hw/arm/virt.h
> > @@ -129,6 +129,7 @@ struct VirtMachineClass {
> >       bool no_kvm_steal_time;
> >       bool acpi_expose_flash;
> >       bool no_secure_gpio;
> > +    bool no_cpu_topology;
> >   };
> >   
> >   struct VirtMachineState {
> > --
> > 2.23.0
>
> .