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

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Message-ID: <20130321185908.GG3637@linux.vnet.ibm.com>
Date:	Thu, 21 Mar 2013 11:59:08 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	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 Thu, Mar 21, 2013 at 02:44:22PM -0400, Steven Rostedt wrote:
> On Thu, 2013-03-21 at 10:15 -0700, Paul E. McKenney wrote:
> 
> > > The OS always has some sched other tasks around that become runnable after
> > > a while (like for example the vm statistics update, or the notorious slab
> > > scanning). As long as SCHED_FIFO is active and there is no process in the
> > > same scheduling class then tick needs to be off. Also wish that this would
> > > work with SCHED_OTHER if there is only a single task with a certain renice
> > > value (-10?) and the rest is runnable at lower priorities. Maybe in that
> > > case stop the tick for a longer period and then give the lower priority
> > > tasks a chance to run but then switch off the tick again.
> > 
> > These sound to me like good future enhancements.
> 
> Exactly. Please, this is a complex enough change to something that is
> critical to the entire system (similar to RCU itself). Lets take baby
> steps here and get it right each step of the way.
> 
> For now, no, if more than one process is scheduled on the CPU, we fall
> out of dynamic tick mode. In the future, we can add SCHED_FIFO task
> scheduled in to trigger it. But lets conquer that after we successfully
> conquer the current changes.

What Steve said!!!

							Thanx, Paul

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