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Re: [Qemu-devel] [PATCH 3/4] acpi: provide _PXM method for CPU devices i

From: Marcel Apfelbaum
Subject: Re: [Qemu-devel] [PATCH 3/4] acpi: provide _PXM method for CPU devices if QEMU is started numa enabled
Date: Thu, 30 Jun 2016 16:11:44 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0

On 06/30/2016 04:01 PM, Igor Mammedov wrote:
On Thu, 30 Jun 2016 15:48:54 +0300
Marcel Apfelbaum <address@hidden> 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 <address@hidden>
   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"

@@ -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 
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

I have nothing against this approach.


Reviewed-by: Marcel Apfelbaum <address@hidden>


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