How to create a new Linux kernel scheduler
Looking through the scheduler source code (2.6.34, kernel/sched.c), I can see how the "pluggable" schedulers are used, and I believe I understand the interface to be implemented. What I don't understand yet is how to get my code built into the kernel. At the very least, pointers to other sites would be appreciated.
Right now, I'm grepping for SCHED_FIFO, SCHED_RR, and SCHED_NORMAL in the kernel source tree, so really I'm looking for a more insightful way to look at it :-)
EDIT: As some background, I'm very familiar with the FreeBSD scheduler (and the FreeBSD kernel in general), so I'm not looking for pointers on how to do process/thread level scheduling. I'm looking for a way to add my own scheduler alongside the normal linux schedulers (similar to SCHED_FIFO).
EDIT #2: The BFS pointer below is a good start, but it still rips CFS out of the kernel. sched.c now looks like:
#ifdef CONFIG_SCHED_BFS
#include "sched_bfs.c"
#else
// original sched.c
#endif // CONFIG_SCHED_BFS
I'd love to see an answer or a pointer on how to do this a little better (ie, keep CFS, at least for right now).
EDIT #3: I've answered my own question below, as I think I've figured it out.
Answer
I've figured out the answer to my question, so I thought I'd add it here. Below is the patch that will add a new scheduler to the 2.6.34 vanilla kernel. Right now, I've only compiled the kernel. I fully expect running a system with this EXACT patch will cause it to crash -- so use at your own risk :-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2b7b81d..a2a2b21 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -37,6 +37,7 @@
#define SCHED_RR 2
#define SCHED_BATCH 3
/* SCHED_ISO: reserved but not implemented yet */
+#define SCHED_NEW 4 /* Stealing from SCHED_ISO */
#define SCHED_IDLE 5
/* Can be ORed in to make sure the process is reverted back to SCHED_NORMAL on fork */
#define SCHED_RESET_ON_FORK 0x40000000
diff --git a/init/Kconfig b/init/Kconfig
index eb77e8c..0055d26 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -23,6 +23,11 @@ config CONSTRUCTORS
menu "General setup"
+config SCHED_NEW
+ bool "NEW cpu scheduler"
+ ---help---
+ Brand new scheduler
+
config EXPERIMENTAL
bool "Prompt for development and/or incomplete code/drivers"
---help---
diff --git a/kernel/sched.c b/kernel/sched.c
index 3c2a54f..588960d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1931,6 +1931,7 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep)
#include "sched_idletask.c"
#include "sched_fair.c"
+#include "sched_new.c"
#include "sched_rt.c"
#ifdef CONFIG_SCHED_DEBUG
# include "sched_debug.c"
diff --git a/kernel/sched_new.c b/kernel/sched_new.c
new file mode 100644
index 0000000..c2e269e
--- /dev/null
+++ b/kernel/sched_new.c
@@ -0,0 +1,140 @@
+#ifdef CONFIG_SCHED_NEW
+
+/*
+ * Starting with a simple, 1 runq per cpu scheduler. Don't care
+ * about fairness for right now. Just get it up and running to
+ * verify that we have the interface correct
+ */
+
+static void
+enqueue_task_new(struct rq *rq, struct task_struct *p, int wakeup, bool head)
+{
+}
+
+static void dequeue_task_new(struct rq *rq, struct task_struct *p, int sleep)
+{
+}
+
+static void yield_task_new(struct rq *rq)
+{
+}
+
+static void check_preempt_curr_new(struct rq *rq, struct task_struct *p, int flags)
+{
+}
+
+static struct task_struct *pick_next_task_new(struct rq *rq)
+{
+}
+
+static void put_prev_task_new(struct rq *rq, struct task_struct *p)
+{
+}
+
+#ifdef CONFIG_SMP
+static int select_task_rq_new(struct task_struct *p, int sd_flag, int flags)
+{
+}
+static void pre_schedule_new(struct rq *rq, struct task_struct *prev)
+{
+}
+
+static void post_schedule_new(struct rq *rq)
+{
+}
+
+static void task_woken_new(struct rq *rq, struct task_struct *p)
+{
+}
+
+static void task_waking_new(struct rq *this_rq, struct task_struct *task)
+{
+}
+static void set_cpus_allowed_new(struct task_struct *p,
+ const struct cpumask *new_mask)
+{
+}
+/* Assumes rq->lock is held */
+static void rq_online_new(struct rq *rq)
+{
+}
+
+/* Assumes rq->lock is held */
+static void rq_offline_new(struct rq *rq)
+{
+}
+#endif /* COMFIG_SMP */
+
+static void set_curr_task_new(struct rq *rq)
+{
+}
+
+
+static void task_tick_new(struct rq *rq, struct task_struct *p, int queued)
+{
+}
+
+static void task_fork_new(struct task_struct *p)
+{
+}
+static void switched_from_new(struct rq *rq, struct task_struct *p,
+ int running)
+{
+}
+static void switched_to_new(struct rq *this_rq, struct task_struct *task,
+ int running)
+{
+}
+static void prio_changed_new(struct rq *rq, struct task_struct *p,
+ int oldprio, int running)
+{
+}
+static unsigned int get_rr_interval_new(struct rq *rq, struct task_struct *task)
+{
+}
+
+
+
+static const struct sched_class new_sched_class = {
+ .next = &fair_sched_class,
+ .enqueue_task = enqueue_task_new,
+ .dequeue_task = dequeue_task_new,
+ .yield_task = yield_task_new,
+
+ .check_preempt_curr = check_preempt_curr_new,
+
+ .pick_next_task = pick_next_task_new,
+ .put_prev_task = put_prev_task_new,
+
+#ifdef CONFIG_SMP
+ .select_task_rq = select_task_rq_new,
+
+ .pre_schedule = pre_schedule_new,
+ .post_schedule = post_schedule_new,
+
+ .task_waking = task_waking_new,
+ .task_woken = task_woken_new,
+
+ .set_cpus_allowed = set_cpus_allowed_new,
+
+ .rq_online = rq_online_new,
+ .rq_offline = rq_offline_new,
+#endif
+
+ .set_curr_task = set_curr_task_new,
+ .task_tick = task_tick_new,
+ .task_fork = task_fork_new,
+
+ .switched_from = switched_from_new,
+ .switched_to = switched_to_new,
+
+ .prio_changed = prio_changed_new,
+
+ .get_rr_interval = get_rr_interval_new,
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ .moved_group = NULL
+#endif
+};
+
+#endif /* CONFIG_SCHED_NEW */
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index b5b920a..aaf4beb 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1731,7 +1731,11 @@ static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
}
static const struct sched_class rt_sched_class = {
+#ifdef CONFIG_SCHED_NEW
+ .next = &new_sched_class,
+#else
.next = &fair_sched_class,
+#endif /* CONFIG_SCHED_NEW */
.enqueue_task = enqueue_task_rt,
.dequeue_task = dequeue_task_rt,
.yield_task = yield_task_rt,