.\" $OpenBSD: cpu_xcall.9,v 1.2 2025/07/13 19:36:42 schwarze Exp $
.\"
.\" Copyright (c) 2025 David Gwynne <dlg@openbsd.org>
.\" All rights reserved.
.\"
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.Dd $Mdocdate: July 13 2025 $
.Dt CPU_XCALL 9
.Os
.Sh NAME
.Nm cpu_xcall_set ,
.Nm cpu_xcall ,
.Nm cpu_xcall_sync ,
.Nm XCALL_INITIALIZER
.Nd CPU crosscall API
.Sh SYNOPSIS
.In sys/xcall.h
.Ft void
.Fn cpu_xcall_set "struct xcall *xc" "void (*func)(void *)" "void *arg"
.Ft void
.Fn cpu_xcall "struct cpu_info *ci" "struct xcall *xc"
.Ft void
.Fo cpu_xcall_sync
.Fa "struct cpu_info *ci"
.Fa "void (*func)(void *)"
.Fa "void *arg"
.Fa "const char *wmesg"
.Fc
.Fn XCALL_INITIALIZER "void (*func)(void *)" "void *arg"
.Sh DESCRIPTION
The
CPU crosscall API
supports the dispatch of function execution to a specific CPU
in the kernel.
The functions are run in a software interrupt context at
.Dv IPL_SOFTCLOCK .
.Pp
The
.Fn cpu_xcall_set
function prepares the xcall structure
.Fa xc
to call the function
.Fa func
with argument
.Fa arg
via future calls to
.Fn cpu_xcall .
.Pp
.Fn cpu_xcall
dispatches a call to a function with an argument represented by
.Fa xc
on the CPU specified by the
.Fa ci
cpu_info structure.
The same
.Fa xc
may be scheduled for execution on multiple CPUs concurrently.
.Pp
.Fn cpu_xcall_sync
dispatches a call to the function
.Fa func
with argument
.Fa arg
on the CPU specified by the
.Fa ci
cpu_info structure, and waits for that function to complete.
.Fn cpu_xcall_sync
may sleep waiting for the call to
.Fa func
to complete with
.Fa wmesg
as the wait message.
.Pp
.Fn XCALL_INITIALIZER
initialises a
.Vt xcall
structure to call the function
.Fa func
with argument
.Fa arg
via future calls to
.Fn cpu_xcall .
.Sh CONTEXT
.Fn cpu_xcall_set
and
.Fn cpu_xcall
can be called from process context or from interrupt context.
.Pp
.Fn cpu_xcall_sync
can be called from process context.
.Sh SEE ALSO
.Xr spl 9 ,
.Xr tsleep 9
.Sh HISTORY
The
.Nm
functions first appeared in
.Ox 7.8 .
.Sh AUTHORS
The
.Nm
functions were written by
.An David Gwynne Aq Mt dlg@openbsd.org .