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

[wangyanan (Y)]

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
>
> .