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sys/kern/sched_shim.c

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/*
* Copyright 2026 The FreeBSD Foundation
*
* SPDX-License-Identifier: BSD-2-Clause
*
* This software was developed by Konstantin Belousov <kib@FreeBSD.org>
* under sponsorship from the FreeBSD Foundation.
*/
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/proc.h>
#include <sys/runq.h>
#include <sys/sbuf.h>
#include <sys/sched.h>
#include <sys/sysctl.h>
#include <machine/ifunc.h>
const struct sched_instance *active_sched;
#ifndef __DO_NOT_HAVE_SYS_IFUNCS
#define __DEFINE_SHIM(__m, __r, __n, __p, __a) \
DEFINE_IFUNC(, __r, __n, __p) \
{ \
return (active_sched->__m); \
}
#else
#define __DEFINE_SHIM(__m, __r, __n, __p, __a) \
__r \
__n __p \
{ \
return (active_sched->__m __a); \
}
#endif
#define DEFINE_SHIM0(__m, __r, __n) \
__DEFINE_SHIM(__m, __r, __n, (void), ())
#define DEFINE_SHIM1(__m, __r, __n, __t1, __a1) \
__DEFINE_SHIM(__m, __r, __n, (__t1 __a1), (__a1))
#define DEFINE_SHIM2(__m, __r, __n, __t1, __a1, __t2, __a2) \
__DEFINE_SHIM(__m, __r, __n, (__t1 __a1, __t2 __a2), (__a1, __a2))
DEFINE_SHIM0(load, int, sched_load)
DEFINE_SHIM0(rr_interval, int, sched_rr_interval)
DEFINE_SHIM0(runnable, bool, sched_runnable)
DEFINE_SHIM2(exit, void, sched_exit, struct proc *, p,
struct thread *, childtd)
DEFINE_SHIM2(fork, void, sched_fork, struct thread *, td,
struct thread *, childtd)
DEFINE_SHIM1(fork_exit, void, sched_fork_exit, struct thread *, td)
DEFINE_SHIM2(class, void, sched_class, struct thread *, td, int, class)
DEFINE_SHIM2(nice, void, sched_nice, struct proc *, p, int, nice)
DEFINE_SHIM0(ap_entry, void, sched_ap_entry)
DEFINE_SHIM2(exit_thread, void, sched_exit_thread, struct thread *, td,
struct thread *, child)
DEFINE_SHIM1(estcpu, u_int, sched_estcpu, struct thread *, td)
DEFINE_SHIM2(fork_thread, void, sched_fork_thread, struct thread *, td,
struct thread *, child)
DEFINE_SHIM2(ithread_prio, void, sched_ithread_prio, struct thread *, td,
u_char, prio)
DEFINE_SHIM2(lend_prio, void, sched_lend_prio, struct thread *, td,
u_char, prio)
DEFINE_SHIM2(lend_user_prio, void, sched_lend_user_prio, struct thread *, td,
u_char, pri)
DEFINE_SHIM2(lend_user_prio_cond, void, sched_lend_user_prio_cond,
struct thread *, td, u_char, pri)
DEFINE_SHIM1(pctcpu, fixpt_t, sched_pctcpu, struct thread *, td)
DEFINE_SHIM2(prio, void, sched_prio, struct thread *, td, u_char, prio)
DEFINE_SHIM2(sleep, void, sched_sleep, struct thread *, td, int, prio)
DEFINE_SHIM2(sswitch, void, sched_switch, struct thread *, td, int, flags)
DEFINE_SHIM1(throw, void, sched_throw, struct thread *, td)
DEFINE_SHIM2(unlend_prio, void, sched_unlend_prio, struct thread *, td,
u_char, prio)
DEFINE_SHIM2(user_prio, void, sched_user_prio, struct thread *, td,
u_char, prio)
DEFINE_SHIM1(userret_slowpath, void, sched_userret_slowpath,
struct thread *, td)
DEFINE_SHIM2(add, void, sched_add, struct thread *, td, int, flags)
DEFINE_SHIM0(choose, struct thread *, sched_choose)
DEFINE_SHIM2(clock, void, sched_clock, struct thread *, td, int, cnt)
DEFINE_SHIM1(idletd, void, sched_idletd, void *, dummy)
DEFINE_SHIM1(preempt, void, sched_preempt, struct thread *, td)
DEFINE_SHIM1(relinquish, void, sched_relinquish, struct thread *, td)
DEFINE_SHIM1(rem, void, sched_rem, struct thread *, td)
DEFINE_SHIM2(wakeup, void, sched_wakeup, struct thread *, td, int, srqflags)
DEFINE_SHIM2(bind, void, sched_bind, struct thread *, td, int, cpu)
DEFINE_SHIM1(unbind, void, sched_unbind, struct thread *, td)
DEFINE_SHIM1(is_bound, int, sched_is_bound, struct thread *, td)
DEFINE_SHIM1(affinity, void, sched_affinity, struct thread *, td)
DEFINE_SHIM0(sizeof_proc, int, sched_sizeof_proc)
DEFINE_SHIM0(sizeof_thread, int, sched_sizeof_thread)
DEFINE_SHIM1(tdname, char *, sched_tdname, struct thread *, td)
DEFINE_SHIM1(clear_tdname, void, sched_clear_tdname, struct thread *, td)
DEFINE_SHIM0(do_timer_accounting, bool, sched_do_timer_accounting)
DEFINE_SHIM1(find_l2_neighbor, int, sched_find_l2_neighbor, int, cpu)
DEFINE_SHIM0(init_ap, void, schedinit_ap)
static char sched_name[32] = "ULE";
SET_DECLARE(sched_instance_set, struct sched_selection);
void
sched_instance_select(void)
{
struct sched_selection *s, **ss;
int i;
TUNABLE_STR_FETCH("kern.sched.name", sched_name, sizeof(sched_name));
SET_FOREACH(ss, sched_instance_set) {
s = *ss;
for (i = 0; s->name[i] == sched_name[i]; i++) {
if (s->name[i] == '\0') {
active_sched = s->instance;
return;
}
}
}
/*
* No scheduler matching the configuration was found. If
* there is any scheduler compiled in, at all, use the first
* scheduler from the linker set.
*/
if (SET_BEGIN(sched_instance_set) < SET_LIMIT(sched_instance_set)) {
s = *SET_BEGIN(sched_instance_set);
active_sched = s->instance;
for (i = 0;; i++) {
sched_name[i] = s->name[i];
if (s->name[i] == '\0')
break;
}
}
}
void
schedinit(void)
{
if (active_sched == NULL)
panic("Cannot find scheduler %s", sched_name);
active_sched->init();
}
static void
sched_setup(void *dummy)
{
active_sched->setup();
}
SYSINIT(sched_setup, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, sched_setup, NULL);
static void
sched_initticks(void *dummy)
{
active_sched->initticks();
}
SYSINIT(sched_initticks, SI_SUB_CLOCKS, SI_ORDER_THIRD, sched_initticks,
NULL);
static void
sched_schedcpu(void)
{
active_sched->schedcpu();
}
SYSINIT(schedcpu, SI_SUB_LAST, SI_ORDER_FIRST, sched_schedcpu, NULL);
SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RD | CTLFLAG_MPSAFE, 0,
"Scheduler");
SYSCTL_STRING(_kern_sched, OID_AUTO, name, CTLFLAG_RD, sched_name, 0,
"Scheduler name");
static int
sysctl_kern_sched_available(SYSCTL_HANDLER_ARGS)
{
struct sched_selection *s, **ss;
struct sbuf *sb, sm;
int error;
bool first;
sb = sbuf_new_for_sysctl(&sm, NULL, 0, req);
if (sb == NULL)
return (ENOMEM);
first = true;
SET_FOREACH(ss, sched_instance_set) {
s = *ss;
if (first)
first = false;
else
sbuf_cat(sb, ",");
sbuf_cat(sb, s->name);
}
error = sbuf_finish(sb);
sbuf_delete(sb);
return (error);
}
SYSCTL_PROC(_kern_sched, OID_AUTO, available,
CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
NULL, 0, sysctl_kern_sched_available, "A",
"List of available schedulers");
fixpt_t ccpu;
SYSCTL_UINT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0,
"Decay factor used for updating %CPU");
olceUnsubmitted
Done
Inline Actions

I'd use kern.sched.name here, to match the kern.sched.name knob (see herald comment).

olce: I'd use `kern.sched.name` here, to match the `kern.sched.name` knob (see herald comment).
olceUnsubmitted
Done
Inline Actions

There's the problem here that 4BSD is not the default when it is the only one compiled-in.

Could you change the logic so that, if there's only one scheduler, it is automatically selected?

Additionally, if an explicit scheduler has been passed and is not available, then what about printing a warning and continuing running with some arbitrary one?

olce: There's the problem here that 4BSD is not the default when it is the only one compiled-in.
jrtc27Unsubmitted
Done
Inline Actions
void
- sched_unlend_prio(struct thread *td, u_char prio()
+ sched_unlend_prio(struct thread *td, u_char prio)
{
active_sched->unlend_prio(td, prio);
jrtc27:
jrtc27Unsubmitted
Done
Inline Actions
void
- sched_user_prio(struct thread *td, u_char prio))
+ sched_user_prio(struct thread *td, u_char prio)
{
active_sched->user_prio(td, prio);
jrtc27:
jrtc27Unsubmitted
Done
Inline Actions
s = *ss;
- match = true;
- for (i = 0; s->name[i] != 0 && sched_name[i] != 0;
- i++) {
- if (s->name[i] != sched_name[i]) {
- match = false;
- break;
- }
- }
- if (match) {
- active_sched = s->instance;
- return;
+ for (i = 0; s->name[i] == sched_name[i]; ++i) {
+ if (s->name[i] == '\0') {
+ active_sched = s->instance;
+ return;
+ }
}
}
/*

This currently matches if one is a prefix of the other, since the loop terminates as soon as you hit the terminator of one string and treats it as a match. This is one way of writing a fixed version (I believe), based on lib/libc/string/strcmp.c's structure.

jrtc27: This currently matches if one is a prefix of the other, since the loop terminates as soon as…