[RFC PATCH][SeaBIOS] Add _PXM to CPU objects for NUMA hot-plug

[RFC PATCH][SeaBIOS] Add _PXM to CPU objects for NUMA hot-plug

[Vasilis Liaskovitis]

This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
this to work.

The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when
using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM.
The linux guest kernel parses the SRAT CPU entries at boot time and stores them
in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel
resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit
c4c60524). When the removed cpu is hot-added again, the linux kernel looks up
the hot-added cpu object's _PXM  value instead of somehow re-using the SRAT
entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If
the _PXM value is not found, the CPU is assumed to be on node 0, and it is
hot-plugged in the wrong NUMA node.

Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug
time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry?
Or maybe both ways are valid?

This issue may require a kernel fix alternatively or additionally to the seabios
fix: The kernel can save the originally parsed SRAT entry info somewhere before
it resets it at hot-remove time, and use that info on hot-plug time if the _PXM
value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug
works well against a BIOS with no CPU _PXM info.

Any comments / thoughts are welcome.
---
 src/fw/acpi.c        |    8 +++++++-
 src/fw/ssdt-proc.dsl |    2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/fw/acpi.c b/src/fw/acpi.c
index 8de24c9..85c04fd 100644
--- a/src/fw/acpi.c
+++ b/src/fw/acpi.c
@@ -23,6 +23,7 @@
 #include "src/fw/acpi-dsdt.hex"
 
 u32 acpi_pm1a_cnt VARFSEG;
+struct srat_processor_affinity *cpu;
 
 static void
 build_header(struct acpi_table_header *h, u32 sig, int len, u8 rev)
@@ -244,6 +245,7 @@ encodeLen(u8 *ssdt_ptr, int length, int bytes)
 #define PROC_OFFSET_CPUHEX (*ssdt_proc_name - *ssdt_proc_start + 2)
 #define PROC_OFFSET_CPUID1 (*ssdt_proc_name - *ssdt_proc_start + 4)
 #define PROC_OFFSET_CPUID2 (*ssdt_proc_id - *ssdt_proc_start)
+#define PROC_OFFSET_CPUPXM (*ssdt_proc_pxm - *ssdt_proc_start)
 #define PROC_SIZEOF (*ssdt_proc_end - *ssdt_proc_start)
 #define PROC_AML (ssdp_proc_aml + *ssdt_proc_start)
 
@@ -372,6 +374,7 @@ build_ssdt(void)
     *(ssdt_ptr++) = '_';
 
     // build Processor object for each processor
+    struct srat_processor_affinity *core = cpu;
     int i;
     for (i=0; i<acpi_cpus; i++) {
         memcpy(ssdt_ptr, PROC_AML, PROC_SIZEOF);
@@ -379,7 +382,9 @@ build_ssdt(void)
         ssdt_ptr[PROC_OFFSET_CPUHEX+1] = getHex(i);
         ssdt_ptr[PROC_OFFSET_CPUID1] = i;
         ssdt_ptr[PROC_OFFSET_CPUID2] = i;
+        ssdt_ptr[PROC_OFFSET_CPUPXM] = core->proximity_lo;
         ssdt_ptr += PROC_SIZEOF;
+        core++;
     }
 
     // build "Method(NTFY, 2) {If (LEqual(Arg0, 0x00)) {Notify(CP00, Arg1)} ...}"
@@ -497,6 +502,7 @@ build_srat(void)
     int i;
     u64 curnode;
 
+    cpu = core;
     for (i = 0; i < max_cpu; ++i) {
         core->type = SRAT_PROCESSOR;
         core->length = sizeof(*core);
@@ -620,10 +626,10 @@ acpi_setup(void)
 
     struct fadt_descriptor_rev1 *fadt = build_fadt(pci);
     ACPI_INIT_TABLE(fadt);
-    ACPI_INIT_TABLE(build_ssdt());
     ACPI_INIT_TABLE(build_madt());
     ACPI_INIT_TABLE(build_hpet());
     ACPI_INIT_TABLE(build_srat());
+    ACPI_INIT_TABLE(build_ssdt());
     if (pci->device == PCI_DEVICE_ID_INTEL_ICH9_LPC)
         ACPI_INIT_TABLE(build_mcfg_q35());
 
diff --git a/src/fw/ssdt-proc.dsl b/src/fw/ssdt-proc.dsl
index 407d61e..373cdd7 100644
--- a/src/fw/ssdt-proc.dsl
+++ b/src/fw/ssdt-proc.dsl
@@ -32,6 +32,8 @@ DefinitionBlock ("ssdt-proc.aml", "SSDT", 0x01, "BXPC", "BXSSDT", 0x1)
  * also updating the C code.
  */
         Name(_HID, "ACPI0007")
+        ACPI_EXTRACT_NAME_BYTE_CONST ssdt_proc_pxm
+        Name(_PXM, 0xBB)
         External(CPMA, MethodObj)
         External(CPST, MethodObj)
         External(CPEJ, MethodObj)
-- 
1.7.10.4

Re: [RFC PATCH][SeaBIOS] Add _PXM to CPU objects for NUMA hot-plug

[Vasilis Liaskovitis]

Any comment on this?

On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> this to work.
> 
> The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when
> using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM.
> The linux guest kernel parses the SRAT CPU entries at boot time and stores them
> in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel
> resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit
> c4c60524). When the removed cpu is hot-added again, the linux kernel looks up
> the hot-added cpu object's _PXM  value instead of somehow re-using the SRAT
> entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If
> the _PXM value is not found, the CPU is assumed to be on node 0, and it is
> hot-plugged in the wrong NUMA node.
> 
> Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug
> time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry?
> Or maybe both ways are valid?
> 
> This issue may require a kernel fix alternatively or additionally to the seabios
> fix: The kernel can save the originally parsed SRAT entry info somewhere before
> it resets it at hot-remove time, and use that info on hot-plug time if the _PXM
> value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug
> works well against a BIOS with no CPU _PXM info.
> 
> Any comments / thoughts are welcome.
> ---
>  src/fw/acpi.c        |    8 +++++++-
>  src/fw/ssdt-proc.dsl |    2 ++
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/src/fw/acpi.c b/src/fw/acpi.c
> index 8de24c9..85c04fd 100644
> --- a/src/fw/acpi.c
> +++ b/src/fw/acpi.c
> @@ -23,6 +23,7 @@
>  #include "src/fw/acpi-dsdt.hex"
>  
>  u32 acpi_pm1a_cnt VARFSEG;
> +struct srat_processor_affinity *cpu;
>  
>  static void
>  build_header(struct acpi_table_header *h, u32 sig, int len, u8 rev)
> @@ -244,6 +245,7 @@ encodeLen(u8 *ssdt_ptr, int length, int bytes)
>  #define PROC_OFFSET_CPUHEX (*ssdt_proc_name - *ssdt_proc_start + 2)
>  #define PROC_OFFSET_CPUID1 (*ssdt_proc_name - *ssdt_proc_start + 4)
>  #define PROC_OFFSET_CPUID2 (*ssdt_proc_id - *ssdt_proc_start)
> +#define PROC_OFFSET_CPUPXM (*ssdt_proc_pxm - *ssdt_proc_start)
>  #define PROC_SIZEOF (*ssdt_proc_end - *ssdt_proc_start)
>  #define PROC_AML (ssdp_proc_aml + *ssdt_proc_start)
>  
> @@ -372,6 +374,7 @@ build_ssdt(void)
>      *(ssdt_ptr++) = '_';
>  
>      // build Processor object for each processor
> +    struct srat_processor_affinity *core = cpu;
>      int i;
>      for (i=0; i<acpi_cpus; i++) {
>          memcpy(ssdt_ptr, PROC_AML, PROC_SIZEOF);
> @@ -379,7 +382,9 @@ build_ssdt(void)
>          ssdt_ptr[PROC_OFFSET_CPUHEX+1] = getHex(i);
>          ssdt_ptr[PROC_OFFSET_CPUID1] = i;
>          ssdt_ptr[PROC_OFFSET_CPUID2] = i;
> +        ssdt_ptr[PROC_OFFSET_CPUPXM] = core->proximity_lo;
>          ssdt_ptr += PROC_SIZEOF;
> +        core++;
>      }
>  
>      // build "Method(NTFY, 2) {If (LEqual(Arg0, 0x00)) {Notify(CP00, Arg1)} ...}"
> @@ -497,6 +502,7 @@ build_srat(void)
>      int i;
>      u64 curnode;
>  
> +    cpu = core;
>      for (i = 0; i < max_cpu; ++i) {
>          core->type = SRAT_PROCESSOR;
>          core->length = sizeof(*core);
> @@ -620,10 +626,10 @@ acpi_setup(void)
>  
>      struct fadt_descriptor_rev1 *fadt = build_fadt(pci);
>      ACPI_INIT_TABLE(fadt);
> -    ACPI_INIT_TABLE(build_ssdt());
>      ACPI_INIT_TABLE(build_madt());
>      ACPI_INIT_TABLE(build_hpet());
>      ACPI_INIT_TABLE(build_srat());
> +    ACPI_INIT_TABLE(build_ssdt());
>      if (pci->device == PCI_DEVICE_ID_INTEL_ICH9_LPC)
>          ACPI_INIT_TABLE(build_mcfg_q35());
>  
> diff --git a/src/fw/ssdt-proc.dsl b/src/fw/ssdt-proc.dsl
> index 407d61e..373cdd7 100644
> --- a/src/fw/ssdt-proc.dsl
> +++ b/src/fw/ssdt-proc.dsl
> @@ -32,6 +32,8 @@ DefinitionBlock ("ssdt-proc.aml", "SSDT", 0x01, "BXPC", "BXSSDT", 0x1)
>   * also updating the C code.
>   */
>          Name(_HID, "ACPI0007")
> +        ACPI_EXTRACT_NAME_BYTE_CONST ssdt_proc_pxm
> +        Name(_PXM, 0xBB)
>          External(CPMA, MethodObj)
>          External(CPST, MethodObj)
>          External(CPEJ, MethodObj)
> -- 
> 1.7.10.4
> 

Re: [RFC PATCH][SeaBIOS] Add _PXM to CPU objects for NUMA hot-plug

[Toshi Kani]

On Mon, 2013-11-04 at 11:51 +0100, Vasilis Liaskovitis wrote:
> Any comment on this?
> 
> On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> > this to work.
> > 
> > The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when
> > using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM.
> > The linux guest kernel parses the SRAT CPU entries at boot time and stores them
> > in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel
> > resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit
> > c4c60524). When the removed cpu is hot-added again, the linux kernel looks up
> > the hot-added cpu object's _PXM  value instead of somehow re-using the SRAT
> > entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If
> > the _PXM value is not found, the CPU is assumed to be on node 0, and it is
> > hot-plugged in the wrong NUMA node.
> > 
> > Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug
> > time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry?
> > Or maybe both ways are valid?

SRAT describes proximity values at boot-time.  During hotplug, the
kernel is supposed to obtain the current proximity value from _PXM
method.

> > This issue may require a kernel fix alternatively or additionally to the seabios
> > fix: The kernel can save the originally parsed SRAT entry info somewhere before
> > it resets it at hot-remove time, and use that info on hot-plug time if the _PXM
> > value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug
> > works well against a BIOS with no CPU _PXM info.

To support CPU hotplug, seabios needs to implement _PXM to CPU or its
parent device object when the system has multiple nodes.

Thanks,
-Toshi

Re: [RFC PATCH][SeaBIOS] Add _PXM to CPU objects for NUMA hot-plug

[Vasilis Liaskovitis]

Hi Toshi,

On Mon, Nov 04, 2013 at 01:26:14PM -0700, Toshi Kani wrote:
> On Mon, 2013-11-04 at 11:51 +0100, Vasilis Liaskovitis wrote:
> > Any comment on this?
> > 
> > On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> > > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> > > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> > > this to work.
> > > 
> > > The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when
> > > using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM.
> > > The linux guest kernel parses the SRAT CPU entries at boot time and stores them
> > > in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel
> > > resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit
> > > c4c60524). When the removed cpu is hot-added again, the linux kernel looks up
> > > the hot-added cpu object's _PXM  value instead of somehow re-using the SRAT
> > > entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If
> > > the _PXM value is not found, the CPU is assumed to be on node 0, and it is
> > > hot-plugged in the wrong NUMA node.
> > > 
> > > Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug
> > > time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry?
> > > Or maybe both ways are valid?
> 
> SRAT describes proximity values at boot-time.  During hotplug, the
> kernel is supposed to obtain the current proximity value from _PXM
> method.

thanks for the clarification.
> 
> > > This issue may require a kernel fix alternatively or additionally to the seabios
> > > fix: The kernel can save the originally parsed SRAT entry info somewhere before
> > > it resets it at hot-remove time, and use that info on hot-plug time if the _PXM
> > > value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug
> > > works well against a BIOS with no CPU _PXM info.
> 
> To support CPU hotplug, seabios needs to implement _PXM to CPU or its
> parent device object when the system has multiple nodes.

ok, so no linux kernel changes are needed. Only adding PXM to seabios CPUs
objects should be enough, which is what this RFC patch does. 

thanks,

- Vasilis
> 
> 
> 
> 

Re: [RFC PATCH] Add _PXM to CPU objects for NUMA hot-plug

[Kevin O'Connor]

On Mon, Nov 04, 2013 at 11:51:49AM +0100, Vasilis Liaskovitis wrote:
> Any comment on this?
> 
> On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> > this to work.

I think ACPI changes should be done at QEMU.  Going forward, QEMU will
pass the tables into SeaBIOS.

-Kevin

Re: [SeaBIOS] [RFC PATCH] Add _PXM to CPU objects for NUMA hot-plug

[Igor Mammedov]

On Tue, 5 Nov 2013 12:20:29 +0200
Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com> wrote:

> Hi Toshi,
> 
> On Mon, Nov 04, 2013 at 01:26:14PM -0700, Toshi Kani wrote:
> > On Mon, 2013-11-04 at 11:51 +0100, Vasilis Liaskovitis wrote:
> > > Any comment on this?
> > > 
> > > On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> > > > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> > > > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> > > > this to work.
> > > > 
> > > > The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when
> > > > using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM.
> > > > The linux guest kernel parses the SRAT CPU entries at boot time and stores them
> > > > in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel
> > > > resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit
> > > > c4c60524). When the removed cpu is hot-added again, the linux kernel looks up
> > > > the hot-added cpu object's _PXM  value instead of somehow re-using the SRAT
> > > > entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If
> > > > the _PXM value is not found, the CPU is assumed to be on node 0, and it is
> > > > hot-plugged in the wrong NUMA node.
> > > > 
> > > > Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug
> > > > time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry?
> > > > Or maybe both ways are valid?
> > 
> > SRAT describes proximity values at boot-time.  During hotplug, the
> > kernel is supposed to obtain the current proximity value from _PXM
> > method.
quoting ACPI spec 5.0 (5.2.16 System Resource Affinity Table (SRAT)):
"If the Local APIC ID / Local SAPIC ID / Local x2APIC 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."

so _PXM in not MUST have if there is entry for device in SRAT table and it seems Seabios
builds table with possible CPUs included, so kernel just don't use already present info.
Perhaps kernel should be fixed (i.e take affinity from SRAT table first and
override value with _PXM if present).

> 
> thanks for the clarification.
> > 
> > > > This issue may require a kernel fix alternatively or additionally to the seabios
> > > > fix: The kernel can save the originally parsed SRAT entry info somewhere before
> > > > it resets it at hot-remove time, and use that info on hot-plug time if the _PXM
> > > > value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug
> > > > works well against a BIOS with no CPU _PXM info.
> > 
> > To support CPU hotplug, seabios needs to implement _PXM to CPU or its
> > parent device object when the system has multiple nodes.
> 
> ok, so no linux kernel changes are needed. Only adding PXM to seabios CPUs
> objects should be enough, which is what this RFC patch does. 
> 
> thanks,
> 
> - Vasilis
> > 
> > 
> > 
> > 
> 
> _______________________________________________
> SeaBIOS mailing list
> SeaBIOS@seabios.org
> http://www.seabios.org/mailman/listinfo/seabios

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Re: [SeaBIOS] [RFC PATCH] Add _PXM to CPU objects for NUMA hot-plug

[Igor Mammedov]

On Tue, 5 Nov 2013 12:20:29 +0200
Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com> wrote:

[...]
> > > > This issue may require a kernel fix alternatively or additionally to the seabios
> > > > fix: The kernel can save the originally parsed SRAT entry info somewhere before
> > > > it resets it at hot-remove time, and use that info on hot-plug time if the _PXM
> > > > value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug
> > > > works well against a BIOS with no CPU _PXM info.
> > 
> > To support CPU hotplug, seabios needs to implement _PXM to CPU or its
> > parent device object when the system has multiple nodes.

BTW: may we should compare linux behavior with Windows's one. usually MS implements
ACPI spec more strictly.


> ok, so no linux kernel changes are needed. Only adding PXM to seabios CPUs
> objects should be enough, which is what this RFC patch does. 
> 
> thanks,
> 
> - Vasilis
> > 
> > 
> > 
> > 
> 
> _______________________________________________
> SeaBIOS mailing list
> SeaBIOS@seabios.org
> http://www.seabios.org/mailman/listinfo/seabios

Re: [SeaBIOS] [RFC PATCH] Add _PXM to CPU objects for NUMA hot-plug

[Toshi Kani]

On Wed, 2013-11-06 at 13:44 +0100, Igor Mammedov wrote:
> On Tue, 5 Nov 2013 12:20:29 +0200
> Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com> wrote:
> 
> > Hi Toshi,
> > 
> > On Mon, Nov 04, 2013 at 01:26:14PM -0700, Toshi Kani wrote:
> > > On Mon, 2013-11-04 at 11:51 +0100, Vasilis Liaskovitis wrote:
> > > > Any comment on this?
> > > > 
> > > > On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> > > > > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> > > > > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> > > > > this to work.
> > > > > 
> > > > > The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when
> > > > > using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM.
> > > > > The linux guest kernel parses the SRAT CPU entries at boot time and stores them
> > > > > in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel
> > > > > resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit
> > > > > c4c60524). When the removed cpu is hot-added again, the linux kernel looks up
> > > > > the hot-added cpu object's _PXM  value instead of somehow re-using the SRAT
> > > > > entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If
> > > > > the _PXM value is not found, the CPU is assumed to be on node 0, and it is
> > > > > hot-plugged in the wrong NUMA node.
> > > > > 
> > > > > Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug
> > > > > time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry?
> > > > > Or maybe both ways are valid?
> > > 
> > > SRAT describes proximity values at boot-time.  During hotplug, the
> > > kernel is supposed to obtain the current proximity value from _PXM
> > > method.
> quoting ACPI spec 5.0 (5.2.16 System Resource Affinity Table (SRAT)):
> "If the Local APIC ID / Local SAPIC ID / Local x2APIC 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."
> 
> so _PXM in not MUST have if there is entry for device in SRAT table and it seems Seabios
> builds table with possible CPUs included, so kernel just don't use already present info.
> Perhaps kernel should be fixed (i.e take affinity from SRAT table first and
> override value with _PXM if present).

I think the above statement is to emphasize the need of _PXM for
hotplug, but I will check the intention of the statement.  

Here is a quote from ACPI 5.0, which restates what I said before.
===            
17.2.1 System Resource Affinity Table Definition

This optional System Resource Affinity Table (SRAT) provides the boot
time description of the processor and memory ranges belonging to a
system locality. 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.
====

Thanks,
-Toshi



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Re: [RFC PATCH][SeaBIOS] Add _PXM to CPU objects for NUMA hot-plug

[Vasilis Liaskovitis]

Hi,

On Tue, Nov 05, 2013 at 09:52:39PM -0500, Kevin O'Connor wrote:
> On Mon, Nov 04, 2013 at 11:51:49AM +0100, Vasilis Liaskovitis wrote:
> > Any comment on this?
> > 
> > On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote:
> > > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived
> > > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for
> > > this to work.
> 
> I think ACPI changes should be done at QEMU.  Going forward, QEMU will
> pass the tables into SeaBIOS.

ok, I will resend a qemu-side patch.

thanks,

- Vasilis