Date: Tue, 14 Apr 2015 13:19:04 +0300
From: Azat Khuzhin <a3at.mail@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linux Kernel ML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: load average always more then 1 on idle system with dyntick
 (just after boot)
Message-ID: <20150414101904.GG25394@azat>
References: <20150331195248.GA3582@azat>
 <20150414095424.GJ5029@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150414095424.GJ5029@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1463
Lines: 37

On Tue, Apr 14, 2015 at 11:54:24AM +0200, Peter Zijlstra wrote:
> On Tue, Mar 31, 2015 at 10:52:48PM +0300, Azat Khuzhin wrote:
> > Hi all,
> > 
> > On one of machines [SUPERMICRO], after installing fresh kernel
> > (v4.0-rc5-25-g90a5a89), I noticed that loadavg always greater then 1.
> > 
> > I do a lot of digging and finally have more information on this issue:
> > CONFIG_NO_HZ_IDLE=y  # loadavg always > 1
> > CONFIG_HZ_PERIODIC=y # loadavg < 1
> > 
> > After this I tried to disable "nohz" at boot, to determine whether it is
> > statically added code under #ifdef during compilation or not, so I added
> > "nohz=off" to cmdline, and it helps!
> > 
> > Also if you enable preemption loadavg is also < 1:
> > CONFIG_PREEMPT_VOLUNTARY=y
> 
> So you need CONFIG_PREEMPT=n and CONFIG_NO_HZ_IDLE=y for this to happen?

Yep, CONFIG_PREEMPT_NONE=y and CONFIG_NO_HZ_IDLE=y

> That's somewhat odd (and uncommon I think, most everybody has at least
> VOLUNTARY enabled these days).

This is not a big problem for me, I could enable VOLUNTARY, but I don't
think that it will be useful for my workload. But I could be wrong.

> I'll try to look over the code to see if I can find a preempt relation,
> weird that.

Thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/