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
Changed devel (main) task to fix-released since the proposed patch is upstream as of v6.5-rc1.