Re: [Qemu-devel] [RFC PATCH v2] i386: Add _PXM ACPI method to CPU objects

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 27 Nov 2013 14:02:43 +0100
Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com> wrote:

> This patch adds a _PXM method to ACPI CPU objects for the pc machine. The _PXM
> value is derived from the passed in guest info, same way as CPU SRAT entries.
> 
> Currently, CPU SRAT entries are only enabled for cpus that are already present
> in the system. The SRAT entries for hotpluggable processors are disabled (flags
> bit 0 set to 0 in hw/i385/acpi-build.c:build_srat). Section 5.2.16.1 of ACPI
> spec mentions "If the Local APIC ID of a dynamically added processor is not
> present in the SRAT, a _PXM object must exist for the processor’s device or one
> of its ancestors in the ACPI Namespace." Since SRAT entries are not available
> for the hot-pluggable processors, a _PXM method must exist for them. Otherwise,
> the CPU is hot-added in the wrong NUMA node (default node 0).
> 
> Even if CPU SRAT entries are enabled, _PXM method is what the linux kernel
> consults on hot-add time. Section 17.2.1 of ACPI spec mentions " OSPM will
> consume the SRAT only at boot time. OSPM should use _PXM for any devices that
> are hot-added into the system after boot up." To be more precise if SRAT
> information is available to the guest kernel, it is used.  However, parsed SRAT
> info is reset and lost after hot-remove operations, see kernel commit c4c60524.
> This means that on a hot-unplug / hot-replug scenario, and without a _PXM
> method, the kernel may put a CPU on different nodes because SRAT info has been
> reset by a previous hot-remove operation.
> 
> The above hot-remove/hot-add scenario has been tested on master, plus cpu-del
> patches from:
> https://lists.gnu.org/archive/html/qemu-devel/2013-10/msg01085.html
> With the curret _PXM patch, hot-added CPUs are always placed into the correct
> NUMA node, regardless of kernel behaviour.
> 
> v1->v2:
>    Make method return a DWORD integer
>    Tested on qemu master + cpu-del patches
> 
> Signed-off-by: Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>
> Reviewed-by: Thilo Fromm <t-lo@thilo-fromm.de>
Patch looks good,
Please add patch to update hw/i386/ssdt-proc.hex.generated for hosts without iasl
for completness

> 
> ---
>  hw/i386/acpi-build.c  |    5 +++++
>  hw/i386/ssdt-proc.dsl |    5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index d089e1e..3c11ddc 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -603,6 +603,7 @@ static inline char acpi_get_hex(uint32_t val)
>  #define ACPI_PROC_OFFSET_CPUHEX (*ssdt_proc_name - *ssdt_proc_start + 2)
>  #define ACPI_PROC_OFFSET_CPUID1 (*ssdt_proc_name - *ssdt_proc_start + 4)
>  #define ACPI_PROC_OFFSET_CPUID2 (*ssdt_proc_id - *ssdt_proc_start)
> +#define ACPI_PROC_OFFSET_CPUPXM (*ssdt_proc_pxm - *ssdt_proc_start)
>  #define ACPI_PROC_SIZEOF (*ssdt_proc_end - *ssdt_proc_start)
>  #define ACPI_PROC_AML (ssdp_proc_aml + *ssdt_proc_start)
>  
> @@ -724,6 +725,10 @@ build_ssdt(GArray *table_data, GArray *linker,
>              proc[ACPI_PROC_OFFSET_CPUHEX+1] = acpi_get_hex(i);
>              proc[ACPI_PROC_OFFSET_CPUID1] = i;
>              proc[ACPI_PROC_OFFSET_CPUID2] = i;
> +            proc[ACPI_PROC_OFFSET_CPUPXM] = guest_info->node_cpu[i];
> +            proc[ACPI_PROC_OFFSET_CPUPXM + 1] = 0;
> +            proc[ACPI_PROC_OFFSET_CPUPXM + 2] = 0;
> +            proc[ACPI_PROC_OFFSET_CPUPXM + 3] = 0;
>          }
>  
>          /* build this code:
> diff --git a/hw/i386/ssdt-proc.dsl b/hw/i386/ssdt-proc.dsl
> index 8229bfd..8d4c5bf 100644
> --- a/hw/i386/ssdt-proc.dsl
> +++ b/hw/i386/ssdt-proc.dsl
> @@ -47,6 +47,8 @@ DefinitionBlock ("ssdt-proc.aml", "SSDT", 0x01, "BXPC", "BXSSDT", 0x1)
>   * also updating the C code.
>   */
>          Name(_HID, "ACPI0007")
> +        ACPI_EXTRACT_NAME_DWORD_CONST ssdt_proc_pxm
> +        Name(PXM, 0xAAAAAAAA)
>          External(CPMA, MethodObj)
>          External(CPST, MethodObj)
>          External(CPEJ, MethodObj)
> @@ -59,5 +61,8 @@ DefinitionBlock ("ssdt-proc.aml", "SSDT", 0x01, "BXPC", "BXSSDT", 0x1)
>          Method(_EJ0, 1, NotSerialized) {
>              CPEJ(ID, Arg0)
>          }
> +        Method(_PXM, 0) {
> +            Return (PXM)
> +        }
>      }
>  }