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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2012-03-06 18:54:26 +0100
committerIngo Molnar <mingo@elte.hu>2012-03-12 20:43:17 +0100
commit8e3fabfde445a872c8aec2296846badf24d7c8b4 (patch)
tree60f47d850adc39aff6de56ec82d7e1a13d93d4a8
parent3ccf3e8306156a28213adc720aba807e9a901ad5 (diff)
sched: Update yield() docs
Suggested-by: Joe Perches <joe@perches.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1331056466.11248.327.camel@twins Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/sched/core.c20
1 files changed, 18 insertions, 2 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8781cec7c3e6..47614a5cdd47 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4577,8 +4577,24 @@ EXPORT_SYMBOL(__cond_resched_softirq);
/**
* yield - yield the current processor to other threads.
*
- * This is a shortcut for kernel-space yielding - it marks the
- * thread runnable and calls sys_sched_yield().
+ * Do not ever use this function, there's a 99% chance you're doing it wrong.
+ *
+ * The scheduler is at all times free to pick the calling task as the most
+ * eligible task to run, if removing the yield() call from your code breaks
+ * it, its already broken.
+ *
+ * Typical broken usage is:
+ *
+ * while (!event)
+ * yield();
+ *
+ * where one assumes that yield() will let 'the other' process run that will
+ * make event true. If the current task is a SCHED_FIFO task that will never
+ * happen. Never use yield() as a progress guarantee!!
+ *
+ * If you want to use yield() to wait for something, use wait_event().
+ * If you want to use yield() to be 'nice' for others, use cond_resched().
+ * If you still want to use yield(), do not!
*/
void __sched yield(void)
{