Re: [RFC PATCH v3 3/9] hw/arm/virt: Add cpu-map to device tree

["wangyanan (Y)" <wangyanan55@huawei.com>]

Hi Drew,

On 2021/5/17 14:41, Andrew Jones wrote:
> On Sun, May 16, 2021 at 06:28:54PM +0800, Yanan Wang wrote:
>> From: Andrew Jones <drjones@redhat.com>
>>
>> Support device tree CPU topology descriptions.
>>
>> In accordance with the Devicetree Specification, the Linux Doc
>> "arm/cpus.yaml" requires that cpus and cpu nodes in the DT are
>> present. And we meet the requirement by creating /cpus/cpu@*
>> nodes for members within ms->smp.cpus.
>>
>> Correspondingly, we should also create subnodes in cpu-map for
>> the present cpus, each of which relates to an unique cpu node.
>>
>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>> Co-developed-by: Yanan Wang <wangyanan55@huawei.com>
>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
>> ---
>>   hw/arm/virt.c | 41 ++++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 40 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index c07841e3a4..e5dcdebdbc 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -349,10 +349,11 @@ 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
> Rather than aligning the top line with the lower lines, we could remove
> the extra space from the lower lines. Or, leave the formatting as it was,
> by putting 'See' where 'From' was, like I did in my original patch.
I think I prefer removing the extra space from the lower lines, which is
the right thing to do.
>>        *  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
>> @@ -405,8 +406,46 @@ static void fdt_add_cpu_nodes(const VirtMachineState *vms)
>>                   ms->possible_cpus->cpus[cs->cpu_index].props.node_id);
>>           }
>>   
>> +        if (!vmc->no_cpu_topology) {
>> +            qemu_fdt_setprop_cell(ms->fdt, nodename, "phandle",
>> +                                  qemu_fdt_alloc_phandle(ms->fdt));
>> +        }
>> +
>>           g_free(nodename);
>>       }
>> +
>> +    if (!vmc->no_cpu_topology) {
>> +        /*
>> +         * See Linux Documentation/devicetree/bindings/cpu/cpu-topology.txt
>> +         * In a SMP system, the hierarchy of CPUs is defined through four
>> +         * entities that are used to describe the layout of physical CPUs
> s/entities/levels/
Above comment was completely from Linux Doc cpu-topology.txt. See [1].
I think entities may be more reasonable than levels here, since there can be
multiple levels of clusters in cpu-map which makes the total not four.

[1] 
https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/cpu/cpu-topology.txt
>> +         * in the system: socket/cluster/core/thread.
> The comment says there are four levels including 'cluster', but there's no
> 'cluster' below.
According to Doc [1] (line 114), a socket node's child nodes must be
*one or more* cluster nodes which means cluster is mandatory to be
socket's child in DT.

So I think maybe we should just keep the comment as-is, and change
the map-path from /cpus/cpu-map/socket*/cores*/threads* to
/cpus/cpu-map/socket*/cluster0/cores*/threads* in this patch?

Thanks,
Yanan
>> +         */
>> +        qemu_fdt_add_subnode(ms->fdt, "/cpus/cpu-map");
>> +
>> +        for (cpu = 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",
>> +                    "socket", cpu / (ms->smp.cores * ms->smp.threads),
>> +                    "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",
>> +                    "socket", cpu / ms->smp.cores,
>> +                    "core", cpu % ms->smp.cores);
>> +            }
>> +            qemu_fdt_add_path(ms->fdt, map_path);
>> +            qemu_fdt_setprop_phandle(ms->fdt, map_path, "cpu", cpu_path);
>> +
>> +            g_free(map_path);
>> +            g_free(cpu_path);
>> +        }
>> +    }
>>   }
>>   
>>   static void fdt_add_its_gic_node(VirtMachineState *vms)
>> -- 
>> 2.19.1
>>
> Thanks,
> drew
>
> .