As described in
https://community.intel.com/t5/Blogs/Products-and-Solutions/HPC/Enabling-High-Bandwidth-Memory-for-HPC-and-AI-Applications-for/post/1335100,
for Intel Sapphire Rapids CPUs with HBM, it is possible to utilize the HBM as
cache (so called "2LM mode"). It works in the way to create N fake NUMA domains
in a size aligned the HBM so that HBM can act like direct-mapped L4 cache.
Since this is not really a "bug" (but is an officially proposed use case
from Intel), it's not likely to provide a test case. But from HPE's
testing of the test kernel from comment 2, there is improvement to
performance on a Sapphire Rapids CPU with HBM.
** Changed in: linux (Ubuntu Jammy)
Status: Incomplete => Confirmed
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https://bugs.launchpad.net/bugs/2008745
Title:
[SRU] Intel Sapphire Rapids HBM support needs CONFIG_NUMA_EMU
Status in linux package in Ubuntu:
Incomplete
Status in linux source package in Jammy:
Confirmed
Status in linux source package in Kinetic:
New
Status in linux source package in Lunar:
Incomplete
Bug description:
[Impact]
Currently Ubuntu kernel has this kernel config disabled.
But in some cases, Intel's Sapphire Rapids High Bandwith
Memory (SPR-HBM) needs this option.
Memory bandwidth has been a bottleneck of increasingly memory bound
workloads. Sapphire Rapids plus HBM is specifically targeted to
cater to these workloads, traditionally served using overprovisioning
of memory devices.
Please search the keyword "fake numa" in
https://community.intel.com/t5/Blogs/Products-and-
Solutions/HPC/Enabling-High-Bandwidth-Memory-for-HPC-and-AI-
Applications-for/post/1335100
[Fix]
Enable CONFIG_NUMA_EMU in our kernel config for 5.15 and later
[Test Plan]
[Where problems could occur]
The regression risk is low
[Other Info]
Jammy
https://code.launchpad.net/~mreed8855/ubuntu/+source/linux/+git/jammy/+ref/lp_2008745_config_numa_emu
Kinetic
https://code.launchpad.net/~mreed8855/ubuntu/+source/linux/+git/kinetic/+ref/lp_2008745_config_numa_emu_kinetic
Lunar
https://code.launchpad.net/~mreed8855/ubuntu/+source/linux/+git/lunar/+ref/config_numa_emu_lunar
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