linux-kernel - Re: [RFC][PATCH 0/8] sched,idle: need resched polling rework

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Date:	Tue, 3 Jun 2014 20:28:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, nicolas.pitre@...aro.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/8] sched,idle: need resched polling rework

On Tue, Jun 03, 2014 at 07:00:18PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 03, 2014 at 09:52:22AM -0700, Andy Lutomirski wrote:
> > > So you could cheat and set it in pick_next_task_idle() and clear in
> > > put_prev_task_idle(), that way the entire idle loop, when running has it
> > > set.
> > >
> > 
> > Isn't that a little late for sched_ttwu_pending?  I guess it could be
> > okay, but I'm hesitant to muck around with the scheduler innards that
> > much.  I don't see anything that'll break, though.
> 
> Yeah, only later did I see you clear much earlier, which makes sense.

Could we clear it from set_nr_and_not_polling()/set_nr_if_polling()?
That's the only two functions that'll kick a cpu out of its polling
loop, and we're already writing to the word anyhow.
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