CPU_XCALL(9)

💅 CPU_XCALL(9) — Kernel Developer's Manual, bestie ✨

✨ NAME ✨

cpu_xcall_set, cpu_xcall, cpu_xcall_sync, XCALL_INITIALIZER — CPU crosscall API 💖

🦋 SYNOPSIS 🦋

#include <sys/xcall.h>

void
cpu_xcall_set(struct xcall *xc, void (*func)(void *), void *arg);

void
cpu_xcall(struct cpu_info *ci, struct xcall *xc);

void
cpu_xcall_sync(struct cpu_info *ci, void (*func)(void *), void *arg,
    const char *wmesg);

XCALL_INITIALIZER(void (*func)(void *), void *arg);

💖 DESCRIPTION 💖

okay so the CPU crosscall API supports the dispatch of function execution to a specific CPU in the kernel. That's the whole plot, and it slays. ✨ The functions are run in a software interrupt context at IPL_SOFTCLOCK.

Here's the function-by-function tea:

• cpu_xcall_set() — prepares the xcall structure xc to call the function func with argument arg via future calls to cpu_xcall(). It's giving "set it up now, fire it later" energy. 🎀
• cpu_xcall() — dispatches a call to a function with an argument represented by xc on the CPU specified by the ci cpu_info structure. The same xc may be scheduled for execution on multiple CPUs concurrently. No cap. 🔥
• cpu_xcall_sync() — dispatches a call to the function func with argument arg on the CPU specified by the ci cpu_info structure, and waits for that function to complete. It may sleep waiting for the call to func to complete with wmesg as the wait message. 😴
• XCALL_INITIALIZER() — initialises a xcall structure to call the function func with argument arg via future calls to cpu_xcall(). Iconic initializer behaviour, honestly. 💅

🌈 CONTEXT 🌈

• cpu_xcall_set() and cpu_xcall() can be called from process context or from interrupt context.
• cpu_xcall_sync() can be called from process context.

So yes bestie, context matters — that's the vibe check. 🫶

👑 SEE ALSO 👑

• spl(9)
• tsleep(9)

🎀 HISTORY 🎀

The cpu_xcall_set functions first appeared in OpenBSD 7.8. 🎉

💜 AUTHORS 💜

The cpu_xcall_set functions were written by David Gwynne <dlg@openbsd.org>. 🫶

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This page is from Debian, dated July 13, 2025, and it's titled CPU_XCALL(9) — mwah 💋✨