Re: [Qemu-devel] [PATCH 3/4] acpi: provide _PXM method for CPU devices if QEMU is started numa enabled

[Marcel Apfelbaum <marcel@redhat.com>]

On 06/30/2016 04:01 PM, Igor Mammedov wrote:
> On Thu, 30 Jun 2016 15:48:54 +0300
> Marcel Apfelbaum <marcel@redhat.com> wrote:
>
>> On 06/30/2016 03:23 PM, Igor Mammedov wrote:
>>> fixes long standing issue where Linux kernel would assing
>>> hotplugged CPU to 1st numa node as it discards proximity
>>> for hotplugged CPUs after SRAT is parsed.
>>>
>>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
>>> ---
>>>    hw/acpi/cpu.c | 9 +++++++++
>>>    1 file changed, 9 insertions(+)
>>>
>>> diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
>>> index c13b65c..d9cf3ee 100644
>>> --- a/hw/acpi/cpu.c
>>> +++ b/hw/acpi/cpu.c
>>> @@ -4,6 +4,7 @@
>>>    #include "qapi/error.h"
>>>    #include "qapi-event.h"
>>>    #include "trace.h"
>>> +#include "sysemu/numa.h"
>>>
>>>    #define ACPI_CPU_HOTPLUG_REG_LEN 12
>>>    #define ACPI_CPU_SELECTOR_OFFSET_WR 0
>>> @@ -503,6 +504,7 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
>>>
>>>            /* build Processor object for each processor */
>>>            for (i = 0; i < arch_ids->len; i++) {
>>> +            int j;
>>>                Aml *dev;
>>>                Aml *uid = aml_int(i);
>>>                GArray *madt_buf = g_array_new(0, 1, 1);
>>> @@ -546,6 +548,13 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
>>>                              aml_arg(1), aml_arg(2))
>>>                );
>>>                aml_append(dev, method);
>>> +
>>> +            for (j = 0; j < nb_numa_nodes; j++) {
>>> +                if (test_bit(i, numa_info[j].node_cpu)) {
>>> +                    aml_append(dev, aml_name_decl("_PXM", aml_int(j)));
>>> +                }
>>> +            }
>>> +
>>>                aml_append(cpus_dev, dev);
>>>            }
>>>        }
>>>
>>
>> I would add, at least in the commit message, a pointer to the ACPI spec:
>>
>> ACPI 5.0 (6.2.13)
>> -----------------
>> If the Local APIC ID / Local SAPIC ID / Local x2APIC ID of a dynamically added processor is not
>> present in the System Resource Affinity Table (SRAT), a _PXM object must exist for the
>> processor’s device or one of its ancestors in the ACPI Namespace.
>>
>>
>> I suppose we don't have the APIC id in SRAT for all possible CPUs, so it OK.
> we have entries for possible CPUs in SRAT and commit says that Linux discards it,
> hence we need to add _PXM to CPU objects. So broken linux handling would put
> hotplugged CPUs into corrected nodes.
>

OK, so the commit message was misleading: "Fixes" :)
Just flip "Fix" with "Workaround for... "

> To fix it on linux side, ACPI part probably would need to be refactored to store
> parsed tables info somewhere else, so it would be available past boot time
> (not a small undertaking) I'd say.

Maybe we should at least report it to the right mailing list.

> While fixing it on QEMU side is easy and works well even for currently released
> kernels.
>

I have nothing against this approach.

Thanks,
Marcel

>
>>
>>
>> Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
> Thanks!
>
>>
>> Thanks,
>> Marcel
>