Re: [PATCH perf-tools-next] perf list: Avoid repeated strlen when escaping JSON strings

[sashiko-bot@kernel.org]

> The %S conversion in fix_escape_fprintf() calls strlen(s) in the loop
> condition while escaping each character. GCC 14.2.0 retains this call
> inside the loop in a normal DEBUG=0 (-O3) perf build, repeatedly scanning
> the whole string.
> 
> Test the current character for NUL instead. This processes the same bytes
> without rescanning the string. Escaping and buffer growth are unchanged.
> 
> Full-command wall-clock measurements on an Apple M5 Pro host running an
> aarch64 Linux container with GCC 14.2.0 and glibc 2.41 gave these medians:
> 
>   perf list --json metrics       Before (ms)  After (ms)
>   Default catalog                    0.5969      0.5855
>   PERF_CPUID=0x00000000410fd830        0.7818      0.7033
> 
> [ ... ]
> Codex assisted with identifying the redundant scan, preparing the change,
> and running the comparisons.
> 
> Assisted-by: LLM
> Signed-off-by: Qerogram <qerogram@naver.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260910123839.72285-1-qerogram@naver.com?part=1