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.
Currently the implementation of PPTT generation complies with ACPI
specification 5.2.29 (Revision 6.3). The 6.3 spec can be found at:
https://uefi.org/sites/default/files/resources/ACPI_6_3_May16.pdf
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Co-developed-by: Yanan Wang <wangyanan55@huawei.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20211020142125.7516-6-wangyanan55@huawei.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Andrew Jones
099f2df2e6