arch_in_rcu_eqs(9)

💅 arch_in_rcu_eqs(9) — the Kernel API Manual, bestie edition 🎀

okay so welcome to arch_in_rcu_eqs(9), a page from the Kernel API Manual ✨ and honestly? it's giving "small function, huge responsibility" energy. it's a little arch-specific vibe check for RCU extended quiescent states, and we're gonna get into it 🫶

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🌸 NAME 🌸

arch_in_rcu_eqs — an architecture-specific check for RCU extended quiescent states, no cap 💅

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✨ SYNOPSIS ✨

bool arch_in_rcu_eqs (void );

literally just that. one function, zero drama 🦋

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🎀 ARGUMENTS 🎀

• void — no arguments, bestie. nothing goes in. it's a clean slate, main character energy only 👑

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⭐ RETURN ⭐

• true if the CPU is potentially in an RCU EQS
• false otherwise

that's it, that's the whole return contract 🍓

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💖 DESCRIPTION 💖

so here's the tea ☕ — architectures only need to define this if threads other than the idle thread may have an interruptible EQS. this does not need to handle idle threads. got it? good, write that down 📝

and the way that over-estimating is completely fine?? yesss — it's safe to over-estimate, it just costs you redundant RCU management work. so like, being a little extra is allowed here, you just pay for it in vibes (and CPU cycles) 🔥

it's invoked from irqentry_enter — that's the call site, iykyk 💫

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👑 SEE ALSO 👑

the kernel file that lives here: ./include/linux/irq-entry-common.h 📂

and the whole friend group, because this function is never alone:

• arch_enter_from_user_mode(9)
• enter_from_user_mode(9)
• arch_exit_to_user_mode_work(9)
• arch_exit_to_user_mode_prepare(9)
• arch_exit_to_user_mode(9)
• arch_do_signal_or_restart(9)
• __exit_to_user_mode_prepare(9)
• syscall_exit_to_user_mode_prepare(9)
• irqentry_exit_to_user_mode_prepare(9)
• exit_to_user_mode(9)
• irqentry_enter_from_user_mode(9)
• irqentry_exit_to_user_mode(9)
• struct irqentry_state(9)
• irqentry_enter_from_kernel_mode(9)
• irqentry_exit_to_kernel_mode_preempt(9)
• irqentry_exit_to_kernel_mode_after_preempt(9)
• irqentry_exit_to_kernel_mode(9)
• irqentry_enter(9)
• irqentry_exit(9)
• irqentry_nmi_enter(9)
• irqentry_nmi_exit(9)

like, the entire irqentry cinematic universe 🌈💀 go read them, they ate 💅

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ngl bestie, if you're touching this one you're already deep in arch + irqentry territory — so like, respect, and also please be careful 🧚💜

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and that's the page!! source lives in ./include/linux and the timestamp on this bad boy is October 2026 — go off, you're officially educated on RCU EQS now 🔥👑✨