perf_cpu_map__nr(9)

🌸 perf_cpu_map__nr 🌸

okay so bestie, welcome to perf_cpu_map__nr — the libperf function that tells you how many CPUs are in your map, but with one iconic little plot twist 💅

✨ SYNOPSIS ✨

LIBPERF_API unsigned int perf_cpu_map__nr (const struct perf_cpu_map
*cpus );

🦋 DESCRIPTION 🦋

Alright so here's the tea, and you're gonna want to sit down for this one 🫖

If the map is empty, this thing returns 1. Not 0. 1. And why?? Because perf_cpu_map__cpu returns a cpu of -1 for an invalid index — so an empty map literally ends up looking like it contains the "any CPU"/dummy value. It's giving "empty but make it look like it has one thing in it" 😭 no cap, that's the whole vibe.

Otherwise, the result is the number of CPUs in the map, plus one if the "any CPU"/dummy value is present. So like, count your CPUs, then check if the dummy value is crashing the party — if it is, add one 🎀

💜 ARGUMENTS 💜

• cpus — literally says -- undescribed -- in the source docs, so that's all we got, bestie 🙈 (it's a const struct perf_cpu_map *, iykyk)

👑 SEE ALSO 👑

Go check out the kernel file ./tools/lib/perf/include/perf/cpumap.h, plus these absolute main characters:

• struct perf_cpu(9)
• perf_cpu_map__new_any_cpu(9)
• perf_cpu_map__new_online_cpus(9)
• perf_cpu_map__new(9)
• perf_cpu_map__cpu(9)
• perf_cpu_map__has_any_cpu_or_is_empty(9)
• perf_cpu_map__is_any_cpu_or_is_empty(9)
• perf_cpu_map__is_empty(9)
• perf_cpu_map__min(9)
• perf_cpu_map__max(9)

and that's the whole page, periodt ✨ this lil masterpiece lives over at ./tools/lib/perf/include/perf, stamped October 2026, and it's officially perf_cpu_map__nr(9) — slay, bye bestie 💖🦋🌸