Re: [PATCH v3] perf cpumap: Reduce cpu size from int to int16_t

[James Clark]

On 10/02/2025 7:12 pm, Ian Rogers wrote:
> Fewer than 32k logical CPUs are currently supported by perf. A cpumap
> is indexed by an integer (see perf_cpu_map__cpu) yielding a perf_cpu
> that wraps a 4-byte int for the logical CPU - the wrapping is done
> deliberately to avoid confusing a logical CPU with an index into a
> cpumap. Using a 4-byte int within the perf_cpu is larger than required
> so this patch reduces it to the 2-byte int16_t. For a cpumap
> containing 16 entries this will reduce the array size from 64 to 32
> bytes. For very large servers with lots of logical CPUs the size
> savings will be greater.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
> v3. Add bounds checks as suggested by Leo Yan <leo.yan@xxxxxxx>.
> v2. Rebase and tweak commit message add Reviewed-by: Tim Chen
>      <tim.c.chen@xxxxxxxxxxxxxxx>.
> ---
>   tools/lib/perf/cpumap.c              |  8 ++--
>   tools/lib/perf/include/perf/cpumap.h |  3 +-
>   tools/perf/util/cpumap.c             | 68 +++++++++++++++++++---------
>   tools/perf/util/env.c                |  2 +-
>   4 files changed, 54 insertions(+), 27 deletions(-)

Reviewed-by: James Clark <james.clark@xxxxxxxxxx>