linux-kernel - Re: [PATCH 1/4] sched: Don't account tickless CPU load on tick

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Date:	Tue, 2 Feb 2016 09:50:41 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 1/4] sched: Don't account tickless CPU load on tick

On Mon, Feb 01, 2016 at 11:34:33AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 01, 2016 at 07:05:13PM +0900, Byungchul Park wrote:
> > On Fri, Jan 29, 2016 at 10:50:16AM +0100, Peter Zijlstra wrote:
> > > On Thu, Jan 28, 2016 at 05:01:26PM +0100, Frederic Weisbecker wrote:
> > > > So lets check all the things we call on scheduler_tick():
> > > > 
> > > > _ sched_clock_tick(): maybe it doesn't need to be called when idle. I'm not sure.
> > > >   Some code in idle (timers, irqs, ...) might need to call sched_clock().
> > > 
> > > Only needed if you've got a shady TSC.
> > 
> > Yeh.. IMO, this can be done without the tick handling during nohz, with the
> > patch I am attaching. Could you check the patch? Or we have to handle it
> > remotely, too. (for a crazy TSC)
> 
> I think NOHZ_FULL already requires the TSC not to be wrecked.

What about the regular NOHZ? Or does not any code in idle call a kind of
sched_lock_cpu() at all?