linux-kernel - Re: [PATCH] nohz1: Documentation

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Date:	Mon, 25 Mar 2013 14:31:32 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rob Landley <rob@...dley.net>, linux-kernel@...r.kernel.org,
	josh@...htriplett.org, zhong@...ux.vnet.ibm.com,
	khilman@...aro.org, geoff@...radead.org, tglx@...utronix.de
Subject: Re: [PATCH] nohz1: Documentation

On Fri, 22 Mar 2013, Paul E. McKenney wrote:

> On Fri, Mar 22, 2013 at 02:38:58PM +0000, Christoph Lameter wrote:
> > On Thu, 21 Mar 2013, Paul E. McKenney wrote:
> >
> > > So, how long of busy periods are you contemplating for your SCHED_FIFO
> > > threads?  Is it possible to tune/adjust the offending per-CPU ktheads
> > > to wake up less frequently than that time?
> >
> > Test programs right now run 10 seconds. 30 seconds would definitely be
> > enough for the worst case.
>
> OK, that might be doable for some workloads.  What happens when you
> try tuning the 2-second wakeup interval to (say) 45 seconds?

The vm kernel threads do no useful work if no system calls are being done.
If there is no kernel action then they can be deferred indefinitely.

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