linux-kernel - Re: [ANNOUNCE] 4.4-rc6-rt1

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Date:	Thu, 14 Jan 2016 15:17:44 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Clark Williams <williams@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [ANNOUNCE] 4.4-rc6-rt1

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

>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) {

Sebastian