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

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Date:	Thu, 14 Jan 2016 15:29:11 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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

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

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

	-Mike