On Thu, 2016-01-14 at 15:30 +0100, Thomas Gleixner wrote:

On Thu, 14 Jan 2016, Mike Galbraith wrote:

quoted

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

quoted

quoted

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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

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behaved very badly.

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

I didn't have CONFIG_NO_HZ_FULL enabled, it was CONFIG_NO_HZ_IDLE.

	-Mike