NACK: [SRU][jammy][PATCH 0/1] performance: mm/percpu-internal.h: Re-layout pcpu_chunk to mitigate false sharing

[Philip Cox]

On Wed, 2024-02-14 at 13:07 -0500, Philip Cox wrote:
> BugLink: https://bugs.launchpad.net/bugs/2053152
> 
> SRU Justification:
> 
> [Impact]
> Having 'base_addr' in the same cache line as 'free_bytes',
> 'chunk_md', and
> 'base_addr' causes a performance impact on x86_64 systems which can
> be
> observed while running UnixBench/Excel throughput.
> 
> [Fix]
>  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.
> 
> [Test Plan]
> I have tested this patch, as has Intel.  This patch has been
> upstreamed since 6.5 as well.
> 
> [Where problems could occur]
> The risk for regression is minimal as there should be no logic change
> to the code, and just
> a struct is being ordered differently.  This change has been
> upstreamed for a while with no issues.
> 
> -- 
> 
> 
> Yu Ma (1):
>   percpu-internal/pcpu_chunk: re-layout pcpu_chunk structure to
> reduce
>     false sharing
> 
>  mm/percpu-internal.h | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 

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