preempt/dynamic: Support dynamic preempt with preempt= boot option

Support the preempt= boot option and patch the static call sites
accordingly.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
[remove the mad scientist experiments]
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

kernel/sched/core.c

@@ -12,6 +12,7 @@
 
 #include "sched.h"
 
+#include <linux/entry-common.h>
 #include <linux/nospec.h>
 
 #include <linux/kcov.h>
@@ -4772,9 +4773,73 @@ DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func());
 EXPORT_STATIC_CALL(preempt_schedule_notrace);
 #endif
 
-
 #endif /* CONFIG_PREEMPTION */
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+/*
+ * SC:cond_resched
+ * SC:might_resched
+ * SC:preempt_schedule
+ * SC:preempt_schedule_notrace
+ * SC:irqentry_exit_cond_resched
+ *
+ *
+ * NONE:
+ *   cond_resched               <- __cond_resched
+ *   might_resched              <- RET0
+ *   preempt_schedule           <- NOP
+ *   preempt_schedule_notrace   <- NOP
+ *   irqentry_exit_cond_resched <- NOP
+ *
+ * VOLUNTARY:
+ *   cond_resched               <- __cond_resched
+ *   might_resched              <- __cond_resched
+ *   preempt_schedule           <- NOP
+ *   preempt_schedule_notrace   <- NOP
+ *   irqentry_exit_cond_resched <- NOP
+ *
+ * FULL:
+ *   cond_resched               <- RET0
+ *   might_resched              <- RET0
+ *   preempt_schedule           <- preempt_schedule
+ *   preempt_schedule_notrace   <- preempt_schedule_notrace
+ *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
+ */
+static int __init setup_preempt_mode(char *str)
+{
+	if (!strcmp(str, "none")) {
+		static_call_update(cond_resched, __cond_resched);
+		static_call_update(might_resched, __static_call_return0);
+		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
+		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
+		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
+		pr_info("Dynamic Preempt: %s\n", str);
+	} else if (!strcmp(str, "voluntary")) {
+		static_call_update(cond_resched, __cond_resched);
+		static_call_update(might_resched, __cond_resched);
+		static_call_update(preempt_schedule, (typeof(&preempt_schedule)) NULL);
+		static_call_update(preempt_schedule_notrace, (typeof(&preempt_schedule_notrace)) NULL);
+		static_call_update(irqentry_exit_cond_resched, (typeof(&irqentry_exit_cond_resched)) NULL);
+		pr_info("Dynamic Preempt: %s\n", str);
+	} else if (!strcmp(str, "full")) {
+		static_call_update(cond_resched, __static_call_return0);
+		static_call_update(might_resched, __static_call_return0);
+		static_call_update(preempt_schedule, __preempt_schedule_func());
+		static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func());
+		static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+		pr_info("Dynamic Preempt: %s\n", str);
+	} else {
+		pr_warn("Dynamic Preempt: Unsupported preempt mode %s, default to full\n", str);
+		return 1;
+	}
+	return 0;
+}
+__setup("preempt=", setup_preempt_mode);
+
+#endif /* CONFIG_PREEMPT_DYNAMIC */
+
+
 /*
  * This is the entry point to schedule() from kernel preemption
  * off of irq context.