nohz: Introduce arch_needs_cpu
Allow the architecture to request a normal jiffy tick when the system
goes idle and tick_nohz_stop_sched_tick is called . On s390 the hook is
used to prevent the system going fully idle if there has been an
interrupt other than a clock comparator interrupt since the last wakeup.
On s390 the HiperSockets response time for 1 connection ping-pong goes
down from 42 to 34 microseconds. The CPU cost decreases by 27%.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
LKML-Reference: <20090929122533.402715150@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 0482229..8dc0821 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -98,6 +98,9 @@
extern struct tick_sched *tick_get_tick_sched(int cpu);
extern void tick_check_idle(int cpu);
extern int tick_oneshot_mode_active(void);
+# ifndef arch_needs_cpu
+# define arch_needs_cpu(cpu) (0)
+# endif
# else
static inline void tick_clock_notify(void) { }
static inline int tick_check_oneshot_change(int allow_nohz) { return 0; }