Public bug reported:
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
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Philip Cox (philcox)
Status: In Progress
** Affects: linux (Ubuntu Jammy)
Importance: Undecided
Assignee: Philip Cox (philcox)
Status: In Progress
** Also affects: linux (Ubuntu Jammy)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Jammy)
Assignee: (unassigned) => Philip Cox (philcox)
** Changed in: linux (Ubuntu)
Status: New => In Progress
** Changed in: linux (Ubuntu Jammy)
Status: New => In Progress
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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:
In Progress
Status in linux source package in Jammy:
In Progress
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
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2053152/+subscriptions
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