linux-kernel - Re: [NOHZ] Remove scheduler_tick_max

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Date:	Tue, 11 Nov 2014 16:36:55 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Tejun Heo <tj@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@....qualcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [NOHZ] Remove scheduler_tick_max_deferment

On Tue, Nov 11, 2014 at 08:58:35AM -0600, Christoph Lameter wrote:
> On Mon, 10 Nov 2014, Frederic Weisbecker wrote:
> 
> > Ok, I confess we moved part of that housekeeping to the syscall/exception/interrupt
> > entry path. We did that for cputime accounting and RCU. And it's possible to
> > even do that for timekeeping. But then the kernel entrypoint is going to be extremely
> > costly. It's worth CPU 0 as a sacrificial lamb.
> 
> Well we can redirect to the scheduler setting the task flag and handle
> costly stuff there if necessary?

"there" here is the syscall/exception/interrupt entry path. And like I said, updating
timekeeping from these places is overkill (although we do it in interrupt entry on
dynticks-idle, but we don't have timekeeping when all system is idle).
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