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Re: [PATCH v8 5/8] hw/acpi/aml-build: Add PPTT table


From: wangyanan (Y)
Subject: Re: [PATCH v8 5/8] hw/acpi/aml-build: Add PPTT table
Date: Wed, 20 Oct 2021 20:53:00 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0


On 2021/10/20 20:43, Eric Auger wrote:
Hi,
On 10/20/21 2:27 PM, wangyanan (Y) wrote:
Hi Eric,

On 2021/10/20 19:11, Eric Auger wrote:
Hi Yanan,
On 10/20/21 11:51 AM, wangyanan (Y) wrote:
Hi Eric,

On 2021/10/20 16:02, Eric Auger wrote:
Hi,

On 10/14/21 3:22 PM, Yanan Wang wrote:
From: Andrew Jones <drjones@redhat.com>

Add the Processor Properties Topology Table (PPTT) used to
describe CPU topology information 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 the vendor for the guests, we simply
use sequential integers starting from zero for the non-leaf nodes
but with ID-valid flag unset, so that guest will ignore them and
use table offsets as unique container IDs. And we use logical CPU
IDs for the leaf nodes with the ID-valid flag set, which will 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>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
---
    hw/acpi/aml-build.c         | 60
+++++++++++++++++++++++++++++++++++++
    include/hw/acpi/aml-build.h |  3 ++
    2 files changed, 63 insertions(+)

diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
index b7b9db6888..0d50e88e9d 100644
--- a/hw/acpi/aml-build.c
+++ b/hw/acpi/aml-build.c
@@ -1990,6 +1990,66 @@ void build_processor_hierarchy_node(GArray
*tbl, uint32_t flags,
        }
    }
    +/* ACPI 6.2: 5.2.29 Processor Properties Topology Table (PPTT) */
+void build_pptt(GArray *table_data, BIOSLinker *linker, MachineState
*ms,
+                const char *oem_id, const char *oem_table_id)
+{
+    int pptt_start = table_data->len;
+    int uid = 0;
+    int socket;
+    AcpiTable table = { .sig = "PPTT", .rev = 2,
+                        .oem_id = oem_id, .oem_table_id =
oem_table_id };
Table 5-149 of 6.2 spec (6.2 May 2017) tells the rev shall be 1. Or is
it an erratum somewhere I did miss?
Yes, the revision in 6.2 spec is 1. And it's 2 in spec 6.3.
So just to be sure, should I use the oldest revision ?
If you need (and use) features (such as flags) introduced in 6.3 then
you should say the code complies with 6.3 and update the above comment.
The comment /* ACPI 6.2: 5.2.29 Processor Properties Topology Table
(PPTT) */
tried to explain the first spec version where PPTT is introduced is 6.2.
But it may
adds some confusion. I think it's better to replace it with:
/*
  * ACPI spec 5.2.29 Processor Properties Topology Table (PPTT)
  * (Revision 6.2 or later)
  */

just like our build_slit().
That's not my understanding. I think we usually point to the latest spec
revision you comply with, ie. in that case 6.3 chapter ...
Ok, I get it. Would
/*
 * ACPI spec, Revision 6.3
 * 5.2.29 Processor Properties Topology Table (PPTT)
 */
be ok ?

Thanks,
Yanan
Thanks

Eric
I would also add the spec version in the commit msg.
+
+    acpi_table_begin(&table, table_data);
+
+    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,
+            /*
+             * ACPI 6.2 - Physical package
+             * represents the boundary of a physical package
+             */
+            (1 << 0),
+            0, socket, NULL, 0);
I see we set an ACPI process ID but in the meantime the ACPI processor
ID valid flag is not set. I am not sure I fully catch the meaning of
this latter but just to double check if this is done on purpose.
Yes, it's on purpose.
Maybe
wort a general comment as this also happens below.
The ID of the container node is invalid and ID of the leaf node is
valid.
The commit message by Andrew has explained why (reason 3). I think
it may be clear enough to explain there why we don't need a valid ID
for the container node.
+
+        for (core = 0; core < ms->smp.cores; core++) {
+            uint32_t core_offset = table_data->len - pptt_start;
+            int thread;
+
+            if (ms->smp.threads > 1) {
+                build_processor_hierarchy_node(
+                    table_data,
+                    /*
+                     * ACPI 6.2 - Physical package
+                     * doesn't represent the boundary of a physical
package
+                     */
+                    (0 << 0),
would rather say (0 << 0) /* not a physical package */ and same
elsewhere
Ok, thanks.
+                    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 */
So the references look globaly confusing to me. Either it complies to
6.2 or to 6.3. Looks ir rather complies with 6.3. To me, this needs to
be clarified.
ACPI 6.2 in the comment means the flag is introduced in the spec
since 6.2.
The same, ACPI 6.3 means the flag is introduced since 6.3. Maybe I
should
just drop all the version-prefix in the comment ?
Yes I think you can drop those comments and just upgrade the global
compliance with 6.3

I will drop the prefix and keep the rest. And add a generic comment on
top of build_pptt() as I replied above.

Thanks,
Yanan
I would also add the reference it complies to in the
commit msg.
Ok, sure.

Thanks,
Yanan
.
+                        (1 << 3),  /* ACPI 6.3 - Node is a Leaf */
+                        core_offset, uid++, NULL, 0);
+                }
+            } else {
+                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);
+            }
+        }
+    }
+
+    acpi_table_end(linker, &table);
+}
+
    /* build rev1/rev3/rev5.1 FADT */
    void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData
*f,
                    const char *oem_id, const char *oem_table_id)
diff --git a/include/hw/acpi/aml-build.h b/include/hw/acpi/aml-build.h
index 2c457c8f17..b92706388c 100644
--- a/include/hw/acpi/aml-build.h
+++ b/include/hw/acpi/aml-build.h
@@ -493,6 +493,9 @@ void build_processor_hierarchy_node(GArray *tbl,
uint32_t flags,
                                        uint32_t parent, uint32_t id,
                                        uint32_t *priv_rsrc, uint32_t
priv_num);
    +void build_pptt(GArray *table_data, BIOSLinker *linker,
MachineState *ms,
+                const char *oem_id, const char *oem_table_id);
+
    void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData
*f,
                    const char *oem_id, const char *oem_table_id);
Thanks

Eric

.
.
.




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