amd_get_boo...io_numerator(9)

✨ amd_get_boost_ratio_numerator 💅

okay so real talk, this is a page straight out of the Kernel API Manual and it's literally about one tiny function that does one tiny math thing. his name is amd_get_boost_ratio_numerator (iconic, i know, the manpage header truncates him to amd_get_boo...io_numerator(9) like a contact saved with too many emoji 💀). stay with me bestie, it's short and it slays.

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🌸 SYNOPSIS 🌸

int amd_get_boost_ratio_numerator (unsigned int cpu , u64 *numerator );

that's it. two args, one int coming back at you. she's lowkey minimal.

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🎀 ARGUMENTS 🎀

• cpu — which CPU you want the numerator for. like, this one specifically. 🫶
• numerator — the output variable where the numerator goes. it's a pointer, so yeah, you're writing through it. no cap.

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🦋 DESCRIPTION 🦋

so the whole vibe of this function is: figure out which numerator to use for calculating the boost ratio on a CPU. that's the mission. ngl it's giving "small function, big responsibility."

here's the tea on how she picks it though 👑

• on systems that support preferred cores, the numerator is a hardcoded value. cute, simple, done.
• on other systems, it's the highest performance register value. she went and looked it up herself. main character energy.

and then there's this little scenario that matters, okay, listen: if you're booting the system with amd-pstate enabled but preferred cores disabled, the function still returns the correct boost numerator so it matches what the hardware can actually do — even if the preferred cores scheduling hints aren't enabled. so like… the hints are off but the math is still right? yes bestie. that's the whole point. 💖

fr fr this is one of those "the details matter" situations — the value you get back is meant to reflect the hardware, not just whether the scheduling hints got switched on.

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⭐ RETURN ⭐

• 0 when it's a success 🎉
• a negative error code otherwise 😭 (you know the drill)

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🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/kernel/acpi/cppc.c
• amd_detect_prefcore(9)

like, go read those if you want the full lore. iykyk.

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and that's the whole page!! 🍓 this gem lives under ./arch/x86/kernel/acpi and the docs are dated October 2026 — so mark your calendar, screenshot it, send it to the group chat, and remember: numerators are temporary, but reading the manpage is forever 💜🧚‍♀️✨