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Re: [RFC PATCH v2 2/6] hw/arm/virt: DT: Add cpu-map
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [RFC PATCH v2 2/6] hw/arm/virt: DT: Add cpu-map |
Date: |
Tue, 27 Apr 2021 14:36:54 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 |
On 4/27/21 12:04 PM, Andrew Jones wrote:
> On Tue, Apr 27, 2021 at 11:47:17AM +0200, Philippe Mathieu-Daudé wrote:
>> Hi Yanan, Drew,
>>
>> On 4/13/21 10:07 AM, Yanan Wang wrote:
>>> From: Andrew Jones <drjones@redhat.com>
>>>
>>> Support device tree CPU topology descriptions.
>>>
>>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
>>> ---
>>> hw/arm/virt.c | 41 ++++++++++++++++++++++++++++++++++++++++-
>>> include/hw/arm/virt.h | 1 +
>>> 2 files changed, 41 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>>> index 9f01d9041b..f4ae60ded9 100644
>>> --- a/hw/arm/virt.c
>>> +++ b/hw/arm/virt.c
>>> @@ -352,10 +352,11 @@ 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
>>> @@ -408,8 +409,45 @@ 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(ms->fdt, nodename, "phandle",
>>> + qemu_fdt_alloc_phandle(ms->fdt));
>>> + }
>>> +
>>> g_free(nodename);
>>> }
>>> +
>>> + if (ms->smp.cpus > 1 && !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
>>> + * in the system: socket/cluster/core/thread.
>>> + */
>>> + qemu_fdt_add_subnode(ms->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",
>>> + "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)
>>> @@ -2769,6 +2807,7 @@ 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;
>>
>> Bare with me because "machine versioning" is something new to me, I was
>> expecting it to be only related to migrated fields.
>> Why do we need to care about not adding the FDT node in older machines?
>> Shouldn't the guest skip unknown FDT nodes?
>
> It probably should, the question is whether it would. Also, the nodes may
> not be unknown, so the guest will read the information and set up its
> topology as instructed. That topology may not be the same as what was
> getting used by default without the topology description. It's possible
> that a user's application has a dependency on the topology and if that
> topology gets changed under its feat it'll behave differently.
[*]
I see.
> In short, machine versioning isn't just about vmstate, it's also about
> keeping a machine type looking the same to the guest.
Yes, TIL.
> Now, it's possible that we're being overly cautious here, but this compat
> variable doesn't complicate code too much. So I think I'd prefer to use it
> than not.
No problem. Could you or Yanan add your first paragraph ([*], reworded
in the commit description? I don't think a comment in the code is
useful, but having it in the commit is helpful IMO.
Thanks,
Phil.
- Re: [RFC PATCH v2 3/6] hw/arm/virt-acpi-build: Distinguish possible and present cpus, (continued)
[RFC PATCH v2 2/6] hw/arm/virt: DT: Add cpu-map, Yanan Wang, 2021/04/13
[RFC PATCH v2 4/6] hw/acpi/aml-build: Add processor hierarchy node structure, Yanan Wang, 2021/04/13
[RFC PATCH v2 6/6] hw/arm/virt: Replace smp_parse with one that prefers cores, Yanan Wang, 2021/04/13