the attached patch fixes the scheduler's sync-wakeup code to be consistent
on UP as well.
Right now there's a behavioral difference between an UP kernel and an SMP
kernel running on a UP box: sync wakeups (which are only activated on SMP)
can cause a wakeup of a higher prio task, without preemption. On UP
kernels this does not happen. This difference in wakeup behavior is bad.
This patch activates sync wakeups on UP as well - in the cases sync
wakeups are done the waker knows that it will schedule away soon, so this
'delay preemption' decision is correct on UP as well.
The patch compiles & boots fine on both UP and SMP.
Ingo
--- linux/include/linux/wait.h.orig
+++ linux/include/linux/wait.h
@@ -111,15 +111,12 @@ extern void FASTCALL(__wake_up_sync(wait
#define wake_up(x) __wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1)
#define wake_up_nr(x, nr) __wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, nr)
#define wake_up_all(x) __wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 0)
+#define wake_up_all_sync(x) __wake_up_sync((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 0)
#define wake_up_interruptible(x) __wake_up((x),TASK_INTERRUPTIBLE, 1)
#define wake_up_interruptible_nr(x, nr) __wake_up((x),TASK_INTERRUPTIBLE, nr)
#define wake_up_interruptible_all(x) __wake_up((x),TASK_INTERRUPTIBLE, 0)
#define wake_up_locked(x) __wake_up_locked((x), TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE)
-#ifdef CONFIG_SMP
#define wake_up_interruptible_sync(x) __wake_up_sync((x),TASK_INTERRUPTIBLE, 1)
-#else
-#define wake_up_interruptible_sync(x) __wake_up((x),TASK_INTERRUPTIBLE, 1)
-#endif
#define __wait_event(wq, condition) \
do { \
--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -1414,8 +1414,6 @@ void __wake_up_locked(wait_queue_head_t
__wake_up_common(q, mode, 1, 0);
}
-#ifdef CONFIG_SMP
-
/**
* __wake_up - sync- wake up threads blocked on a waitqueue.
* @q: the waitqueue
@@ -1426,6 +1424,8 @@ void __wake_up_locked(wait_queue_head_t
* away soon, so while the target thread will be woken up, it will not
* be migrated to another CPU - ie. the two threads are 'synchronized'
* with each other. This can prevent needless bouncing between CPUs.
+ *
+ * On UP it can prevent extra preemption.
*/
void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
@@ -1442,8 +1442,6 @@ void __wake_up_sync(wait_queue_head_t *q
spin_unlock_irqrestore(&q->lock, flags);
}
-#endif
-
void complete(struct completion *x)
{
unsigned long flags;
-
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This archive was generated by hypermail 2b29 : Fri May 23 2003 - 22:00:33 EST