Re: [RFC PATCH v3 8/9] hw/arm/virt-acpi-build: Generate PPTT table

[Andrew Jones]

On Sun, May 16, 2021 at 06:28:59PM +0800, Yanan Wang wrote:
> From: Andrew Jones <drjones@redhat.com>
> 
> Add the Processor Properties Topology Table (PPTT) to expose
> CPU topology information defined by users to ACPI guests.
> 
> Note, a DT-boot Linux guest with a non-flat CPU topology will
> see socket and core IDs being sequential integers starting
> from zero, which is different from ACPI-boot Linux guest,
> e.g. with -smp 4,sockets=2,cores=2,threads=1
> 
> a DT boot produces:
> 
>  cpu:  0 package_id:  0 core_id:  0
>  cpu:  1 package_id:  0 core_id:  1
>  cpu:  2 package_id:  1 core_id:  0
>  cpu:  3 package_id:  1 core_id:  1
> 
> an ACPI boot produces:
> 
>  cpu:  0 package_id: 36 core_id:  0
>  cpu:  1 package_id: 36 core_id:  1
>  cpu:  2 package_id: 96 core_id:  2
>  cpu:  3 package_id: 96 core_id:  3
> 
> This is due to several reasons:
> 
>  1) DT cpu nodes do not have an equivalent field to what the PPTT
>     ACPI Processor ID must be, i.e. something equal to the MADT CPU
>     UID or equal to the UID of an ACPI processor container. In both
>     ACPI cases those are platform dependant IDs assigned by the
>     vendor.
> 
>  2) While QEMU is the vendor for a guest, if the topology specifies
>     SMT (> 1 thread), then, with ACPI, it is impossible to assign a
>     core-id the same value as a package-id, thus it is not possible
>     to have package-id=0 and core-id=0. This is because package and
>     core containers must be in the same ACPI namespace and therefore
>     must have unique UIDs.
> 
>  3) ACPI processor containers are not mandatorily required for PPTT
>     tables to be used and, due to the limitations of which IDs are
>     selected described above in (2), they are not helpful for QEMU,
>     so we don't build them with this patch. In the absence of them,
>     Linux assigns its own unique IDs. The maintainers have chosen not
>     to use counters from zero, but rather ACPI table offsets, which
>     explains why the numbers are so much larger than with DT.
> 
>  4) When there is no SMT (threads=1) the core IDs for ACPI boot guests
>     match the logical CPU IDs, because these IDs must be equal to the
>     MADT CPU UID (as no processor containers are present), and QEMU
>     uses the logical CPU ID for these MADT IDs.
> 
> So in summary, with QEMU as vender for guest, we use sequential integers
> starting from zero for non-leaf nodes without valid ID flag, so that the
> guest will ignore them and use table offsets as the unique IDs. And we
> also use logical CPU IDs for leaf nodes to be consistent with MADT.
> 
> 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-acpi-build.c | 58 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 57 insertions(+), 1 deletion(-)

Why aren't we adding build_pptt to aml-build.c, like my original patch
does? I don't see anything Arm specific below, at least not if you passed
MachineState instead of VirtMachineState, like my original patch did.

> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 4d64aeb865..b03d57745a 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -435,6 +435,57 @@ build_srat(GArray *table_data, BIOSLinker *linker, 
> VirtMachineState *vms)
>                   vms->oem_table_id);
>  }
>  
> +/* ACPI 6.2: 5.2.29 Processor Properties Topology Table (PPTT) */
> +static void build_pptt(GArray *table_data, BIOSLinker *linker,
> +                       VirtMachineState *vms)
> +{
> +    MachineState *ms = MACHINE(vms);
> +    int pptt_start = table_data->len;
> +    int uid = 0, socket;
> +
> +    acpi_data_push(table_data, sizeof(AcpiTableHeader));
> +
> +    for (socket = 0; socket < ms->smp.sockets; socket++) {
> +        uint32_t socket_offset = table_data->len - pptt_start;
> +        int core;
> +
> +        build_processor_hierarchy_node(
> +            table_data,
> +            (1 << 0), /* ACPI 6.2 - Physical package */
> +            0, socket, NULL, 0);
> +
> +        for (core = 0; core < ms->smp.cores; core++) {
> +            uint32_t core_offset = table_data->len - pptt_start;
> +            int thread;
> +
> +            if (ms->smp.threads <= 1) {

We can't have threads < 1, so this condition should be == 1.

> +                build_processor_hierarchy_node(
> +                    table_data,
> +                    (1 << 1) | /* ACPI 6.2 - ACPI Processor ID valid */
> +                    (1 << 3),  /* ACPI 6.3 - Node is a Leaf */
> +                    socket_offset, uid++, NULL, 0);
> +            } else {
> +                build_processor_hierarchy_node(table_data, 0, socket_offset,
> +                                               core, NULL, 0);
> +
> +                for (thread = 0; thread < ms->smp.threads; thread++) {
> +                    build_processor_hierarchy_node(
> +                        table_data,
> +                        (1 << 1) | /* ACPI 6.2 - ACPI Processor ID valid */
> +                        (1 << 2) | /* ACPI 6.3 - Processor is a Thread */
> +                        (1 << 3),  /* ACPI 6.3 - Node is a Leaf */
> +                        core_offset, uid++, NULL, 0);
> +                }
> +            }
> +        }
> +    }
> +
> +    build_header(linker, table_data,
> +                 (void *)(table_data->data + pptt_start), "PPTT",
> +                 table_data->len - pptt_start, 2,
> +                 vms->oem_id, vms->oem_table_id);
> +}
> +
>  /* GTDT */
>  static void
>  build_gtdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
> @@ -719,13 +770,18 @@ void virt_acpi_build(VirtMachineState *vms, 
> AcpiBuildTables *tables)
>      dsdt = tables_blob->len;
>      build_dsdt(tables_blob, tables->linker, vms);
>  
> -    /* FADT MADT GTDT MCFG SPCR pointed to by RSDT */
> +    /* FADT MADT PPTT GTDT MCFG SPCR pointed to by RSDT */
>      acpi_add_table(table_offsets, tables_blob);
>      build_fadt_rev5(tables_blob, tables->linker, vms, dsdt);
>  
>      acpi_add_table(table_offsets, tables_blob);
>      build_madt(tables_blob, tables->linker, vms);
>  
> +    if (!vmc->no_cpu_topology) {
> +        acpi_add_table(table_offsets, tables_blob);
> +        build_pptt(tables_blob, tables->linker, vms);
> +    }
> +
>      acpi_add_table(table_offsets, tables_blob);
>      build_gtdt(tables_blob, tables->linker, vms);
>  
> -- 
> 2.19.1
>

Thanks,
drew