[PATCH] sched: add above_background_load() function

Add an above_background_load() function which can be used by other
subsystems to detect if there is anything besides niced tasks running.

Place it in sched.h to allow it to be compiled out if not used.

Unused for now, but it is a useful hint to the IO scheduler and to
swap-prefetch.
Signed-off-by: Con Kolivas <kernel@kolivas.org>
Cc: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -786,6 +786,22 @@ extern int partition_sched_domains(cpumask_t *partition1,
 
 #endif	/* CONFIG_SMP */
 
+/*
+ * A runqueue laden with a single nice 0 task scores a weighted_cpuload of
+ * SCHED_LOAD_SCALE. This function returns 1 if any cpu is laden with a
+ * task of nice 0 or enough lower priority tasks to bring up the
+ * weighted_cpuload
+ */
+static inline int above_background_load(void)
+{
+	unsigned long cpu;
+
+	for_each_online_cpu(cpu) {
+		if (weighted_cpuload(cpu) >= SCHED_LOAD_SCALE)
+			return 1;
+	}
+	return 0;
+}
 
 struct io_context;			/* See blkdev.h */
 struct cpuset;