On Thu, 14 Jan 2016, Mike Galbraith wrote:

On Thu, 2016-01-14 at 15:17 +0100, Sebastian Andrzej Siewior wrote:

quoted

* Sebastian Andrzej Siewior | 2016-01-13 18:58:45 [+0100]:

quoted

This is due to NO_HZ as far as I can tell. My AMD A10 in idle mode
has
0.7% utilisation of ksoftirqd/ with CONFIG_HZ_PERIODIC and with
CONFIG_NO_HZ_FULL it shows about 25% on all CPU threads.

This should fixed it:

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c

@@ -1453,7 +1453,7 @@ u64 get_next_timer_interrupt(unsigned long

basej, u64 basem)
 	 * the base lock to check when the next timer is pending and
so
 	 * we assume the next jiffy.
 	 */
-	return basej;
+	return basem + TICK_NSEC;
 #endif
 	spin_lock(&base->lock);
 	if (base->active_timers) {

That's what I had done to stop the screaming interrupt, but box still
behaved very badly.

If you turn off CONFIG_NO_HZ_FULL and switch to NO_HZ_IDLE is it still bad?

Thanks,

	tglx