sched: Add /debug/sched_preempt

Add a debugfs file to muck about with the preempt mode at runtime.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/YAsGiUYf6NyaTplX@hirez.programming.kicks-ass.net

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c067176edc5919cee8f4b81ef1287fb2066c507..4a17bb5f28b0f359a4063da31a09d12ae35e63a5 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5363,37 +5363,154 @@ EXPORT_STATIC_CALL(preempt_schedule_notrace);
  *   preempt_schedule_notrace   <- preempt_schedule_notrace
  *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
  */
-static int __init setup_preempt_mode(char *str)
+
+enum {
+       preempt_dynamic_none = 0,
+       preempt_dynamic_voluntary,
+       preempt_dynamic_full,
+};
+
+static int preempt_dynamic_mode = preempt_dynamic_full;
+
+static int sched_dynamic_mode(const char *str)
 {
-       if (!strcmp(str, "none")) {
+       if (!strcmp(str, "none"))
+               return 0;
+
+       if (!strcmp(str, "voluntary"))
+               return 1;
+
+       if (!strcmp(str, "full"))
+               return 2;
+
+       return -1;
+}
+
+static void sched_dynamic_update(int mode)
+{
+       /*
+        * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
+        * the ZERO state, which is invalid.
+        */
+       static_call_update(cond_resched, __cond_resched);
+       static_call_update(might_resched, __cond_resched);
+       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);
+
+       switch (mode) {
+       case preempt_dynamic_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")) {
+               pr_info("Dynamic Preempt: none\n");
+               break;
+
+       case preempt_dynamic_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")) {
+               pr_info("Dynamic Preempt: voluntary\n");
+               break;
+
+       case preempt_dynamic_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);
+               pr_info("Dynamic Preempt: full\n");
+               break;
+       }
+
+       preempt_dynamic_mode = mode;
+}
+
+static int __init setup_preempt_mode(char *str)
+{
+       int mode = sched_dynamic_mode(str);
+       if (mode < 0) {
+               pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
                return 1;
        }
+
+       sched_dynamic_update(mode);
        return 0;
 }
 __setup("preempt=", setup_preempt_mode);
 
+#ifdef CONFIG_SCHED_DEBUG
+
+static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf,
+                                  size_t cnt, loff_t *ppos)
+{
+       char buf[16];
+       int mode;
+
+       if (cnt > 15)
+               cnt = 15;
+
+       if (copy_from_user(&buf, ubuf, cnt))
+               return -EFAULT;
+
+       buf[cnt] = 0;
+       mode = sched_dynamic_mode(strstrip(buf));
+       if (mode < 0)
+               return mode;
+
+       sched_dynamic_update(mode);
+
+       *ppos += cnt;
+
+       return cnt;
+}
+
+static int sched_dynamic_show(struct seq_file *m, void *v)
+{
+       static const char * preempt_modes[] = {
+               "none", "voluntary", "full"
+       };
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(preempt_modes); i++) {
+               if (preempt_dynamic_mode == i)
+                       seq_puts(m, "(");
+               seq_puts(m, preempt_modes[i]);
+               if (preempt_dynamic_mode == i)
+                       seq_puts(m, ")");
+
+               seq_puts(m, " ");
+       }
+
+       seq_puts(m, "\n");
+       return 0;
+}
+
+static int sched_dynamic_open(struct inode *inode, struct file *filp)
+{
+       return single_open(filp, sched_dynamic_show, NULL);
+}
+
+static const struct file_operations sched_dynamic_fops = {
+       .open           = sched_dynamic_open,
+       .write          = sched_dynamic_write,
+       .read           = seq_read,
+       .llseek         = seq_lseek,
+       .release        = single_release,
+};
+
+static __init int sched_init_debug_dynamic(void)
+{
+       debugfs_create_file("sched_preempt", 0644, NULL, NULL, &sched_dynamic_fops);
+       return 0;
+}
+late_initcall(sched_init_debug_dynamic);
+
+#endif /* CONFIG_SCHED_DEBUG */
 #endif /* CONFIG_PREEMPT_DYNAMIC */