[tip: sched/core] preempt/dynamic: Support dynamic preempt with preempt= boot option

["tip-bot2 for Peter Zijlstra (Intel)" <tip-bot2@linutronix.de>]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     4f8a0041162ab74ba5f89ee58f8aad59c4c85d22
Gitweb:        https://git.kernel.org/tip/4f8a0041162ab74ba5f89ee58f8aad59c4c85d22
Author:        Peter Zijlstra (Intel) <peterz@infradead.org>
AuthorDate:    Mon, 18 Jan 2021 15:12:23 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 05 Feb 2021 17:19:58 +01:00

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>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210118141223.123667-9-frederic@kernel.org
---
 kernel/sched/core.c | 67 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 66 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cd0c46f..0562992 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -12,6 +12,7 @@
 
 #include "sched.h"
 
+#include <linux/entry-common.h>
 #include <linux/nospec.h>
 
 #include <linux/kcov.h>
@@ -5314,9 +5315,73 @@ 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, (typeof(&__cond_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, (typeof(&__cond_resched)) __static_call_return0);
+		static_call_update(might_resched, (typeof(&__cond_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.