Expose arm64 CPU topology to userspace
| Affects | Status | Importance | Assigned to | Milestone | |
|---|---|---|---|---|---|
| linux (Ubuntu) |
Fix Released
|
Undecided
|
dann frazier | ||
| Bionic |
Fix Released
|
Undecided
|
dann frazier | ||
Bug Description
[Impact]
Applications, particularly those in the HPC domain (e.g. openmpi), can be optimized for the processor and cache topology. However, the ARM CPU topology isn't correctly exposed to userspace. The kernel's scheduler also uses this information to optimize task placement.
[Fix]
The ACPI 6.2 specification introduced a Processor Properties Topology Table (PPTT). This is what ARM server vendors are using to expose their topology. The linux kernel needs support for parsing this table, and exposing the parsed topology to userspace.
[Test Case]
A HiSilicon D06 without the fix. Note that it thinks I'm on a 24-socket system with 4 cores each. I'm not. I'm on a 2 socket system w/ 48 cores each. An HPC app that optimized for this (bogus) topology would therefore suffer a performance penalty.
ubuntu@d06-1:~$ lscpu
Architecture: aarch64
Byte Order: Little Endian
CPU(s): 96
On-line CPU(s) list: 0-95
Thread(s) per core: 1
Core(s) per socket: 4
Socket(s): 24
NUMA node(s): 4
Vendor ID: 0x48
Model: 0
Stepping: 0x0
BogoMIPS: 200.00
NUMA node0 CPU(s): 0-23
NUMA node1 CPU(s): 24-47
NUMA node2 CPU(s): 48-71
NUMA node3 CPU(s): 72-95
Flags: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics cpuid asimdrdm dcpop
With the fix (and this is correct):
ubuntu@d06-1:~$ lscpu
Architecture: aarch64
Byte Order: Little Endian
CPU(s): 96
On-line CPU(s) list: 0-95
Thread(s) per core: 1
Core(s) per socket: 48
Socket(s): 2
NUMA node(s): 4
Vendor ID: 0x48
Model: 0
Stepping: 0x0
BogoMIPS: 200.00
L1d cache: 64K
L1i cache: 64K
L2 cache: 512K
L3 cache: 32768K
NUMA node0 CPU(s): 0-23
NUMA node1 CPU(s): 24-47
NUMA node2 CPU(s): 48-71
NUMA node3 CPU(s): 72-95
Flags: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics cpuid asimdrdm dcpop
[Regression Risk]
Here's a patch-by patch risk analysis of the changeset:
0001-ACPICA-
Just adds new #defines. No functional change.
0002-drivers-
Moves code down in a file. No functional change. (I double-checked that the moved code is the same).
0003-drivers-
The code this touches is all #ifdef CONFIG_OF, which only applies to the ARM & Power ports of Ubuntu. I've tested on arm64 and regression tested on ppc64el (POWER9). POWER booted fine, and there was no change to lscpu output.
0004-cacheinfo-
Renames a variable, and changes it's type from "struct device_node *" to "void *". No functional change.
0005-arm64-
Adds a new function (but doesn't use it yet).
0006-ACPI-
Adds new code that isn't called yet.
0007-UBUNTU-
Configures on the new code.
0008-ACPI-
Kconfig/Makefile bits for the new code.
0009-drivers-
Finally, we call the new code during initialization, so let's go back and look at that code. The first thing it does is to check for the presence of a PPTT table before proceeding, so the regression risk to systems *without* a PPTT table is negligible. The PPTT table was introduced in the ACPI 6.2 specification, which was released in May 2017. Regression risk should therefore be restricted to systems manufactured (or firmware updated) after that time that happened to include a PPTT table. I don't know of anyone other than ARM licensees doing this - but it's possible there are others. And, it's possible that there's a table out there that tickles a bug in the parsing code. Should that be the case, a hotfix would be to use an initrd to override/strip[*] the PPTT from the XSDT table until a suitable fix is put in place.
0010-arm64-
0011-arm64-
0012-arm64-
These patches only touch arm64 code. I explicitly tested on an arm64 server.
0013-ACPI-
Allows users to override the PPTT table. No change to default behavior.
0014-arm64-
Only touches arm64 code. I explicitly tested on an arm64 server.
[*] https:/
CVE References
| Ubuntu Kernel Bot (ubuntu-kernel-bot) wrote Missing required logs. | #1 |
| Changed in linux (Ubuntu): | |
| status: | New → Incomplete |
| Changed in linux (Ubuntu): | |
| status: | Incomplete → In Progress |
| assignee: | nobody → dann frazier (dannf) |
| description: | updated |
| description: | updated |
| Changed in linux (Ubuntu Bionic): | |
| assignee: | nobody → dann frazier (dannf) |
| description: | updated |
| Changed in linux (Ubuntu Bionic): | |
| status: | New → In Progress |
| description: | updated |
| description: | updated |
| description: | updated |
| description: | updated |
| Changed in linux (Ubuntu Bionic): | |
| status: | In Progress → Fix Committed |
| Brad Figg (brad-figg) wrote | #2 |
| tags: | added: verification-needed-bionic |
| dann frazier (dannf) wrote | #3 |
| tags: |
added: verification-done-bionic removed: verification-needed-bionic |
| Launchpad Janitor (janitor) wrote | #4 |
| Changed in linux (Ubuntu Bionic): | |
| status: | Fix Committed → Fix Released |
| Launchpad Janitor (janitor) wrote | #5 |
| Changed in linux (Ubuntu): | |
| status: | In Progress → Fix Released |
This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:
apport-collect 1770231
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.