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Date: Thu, 14 Jan 2016 15:17:44 +0100
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Clark Williams <williams@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [ANNOUNCE] 4.4-rc6-rt1
Message-ID: <20160114141744.GB17776@linutronix.de>
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* 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