[Bug 2053152] Re: performance: mm/percpu-internal.h: Re-layout pcpu_chunk to mitigate false sharing

This bug is awaiting verification that the linux-xilinx-
zynqmp/5.15.0-1029.33 kernel in -proposed solves the problem. Please
test the kernel and update this bug with the results. If the problem is
solved, change the tag 'verification-needed-jammy-linux-xilinx-zynqmp'
to 'verification-done-jammy-linux-xilinx-zynqmp'. If the problem still
exists, change the tag 'verification-needed-jammy-linux-xilinx-zynqmp'
to 'verification-failed-jammy-linux-xilinx-zynqmp'.


If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.


See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: kernel-spammed-jammy-linux-xilinx-zynqmp-v2 verification-needed-jammy-linux-xilinx-zynqmp

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https://bugs.launchpad.net/bugs/2053152

Title:
performance: mm/percpu-internal.h: Re-layout pcpu_chunk to mitigate
false sharing

Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Jammy:
Fix Released

Bug description:
This is a public version of https://bugs.launchpad.net/bugs/2034984

[Description]
When running UnixBench/Execl throughput case, false sharing is observed due to frequent read on base_addr and write on free_bytes, chunk_md.
UnixBench/Execl represents a class of workload where bash scripts are spawned frequently to do some short jobs. It will do system call on execl frequently, and execl will call mm_init to initialize mm_struct of the process. mm_init will call __percpu_counter_init for percpu_counters initialization. Then pcpu_alloc is called to read the base_addr of pcpu_chunk for memory allocation. Inside pcpu_alloc, it will call pcpu_alloc_area to allocate memory from a specified chunk. This function will update "free_bytes" and "chunk_md" to record the rest free bytes and other meta data for this chunk. Correspondingly, pcpu_free_area will also update these 2 members when free memory.

In current pcpu_chunk layout, `base_addr' is in the same cache line
with `free_bytes' and `chunk_md', and `base_addr' is at the last 8
bytes. This patch moves `bound_map' up to `base_addr', to let
`base_addr' locate in a new cacheline.

[Hardware Information]
Architecture:
Intel / AMD (x86_64)
Platform(s):
Platform-Independent
Date HW is expected at Canonical:

Component(s):
Performance and Scalability

[Software Information]
Target Version:
23.10
Target Kernel:
6.5
Commit IDs:
3a6358c0dbe6 percpu-internal/pcpu_chunk: re-layout pcpu_chunk structure to reduce false sharing
External Links:

[Business Justification]

[Testing guidance]

[External ID]
OSVE-5160


The following requested patch has been applied upstream for v6.5-rc1:

- 3a6358c0dbe6 percpu-internal/pcpu_chunk: re-layout pcpu_chunk
structure to reduce false sharing

https://github.com/torvalds/linux/commit/3a6358c0dbe6a286a4f4504ba392a6039a9fbd12

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