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Subject[tip: sched/core] preempt/dynamic: Support dynamic preempt with preempt= boot option
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 0e79823f55de3cff95894fbb40440b17910e7378
Gitweb: https://git.kernel.org/tip/0e79823f55de3cff95894fbb40440b17910e7378
Author: Peter Zijlstra (Intel) <peterz@infradead.org>
AuthorDate: Mon, 18 Jan 2021 15:12:23 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 09 Feb 2021 16:30:58 +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 | 68 +++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cd0c46f..220393d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5314,9 +5314,75 @@ DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
EXPORT_STATIC_CALL(preempt_schedule_notrace);
#endif

-
#endif /* CONFIG_PREEMPTION */

+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+#include <linux/entry-common.h>
+
+/*
+ * 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.
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