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

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Message-ID: <CALCETrVGGSv51NxMXaD-=9ukkYLTT7DrLTscgA0pa0+PkUYw3Q@mail.gmail.com>
Date:	Tue, 3 Jun 2014 11:44:10 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>
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 3, 2014 at 11:28 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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.

I'd be nervous about this.  I think it could break if
cpuidle_idle_call decides not to idle for any reason, and there is
plenty of complicated code in there.

I'm currently working on some patches that might make this clearer.
Give me a bit.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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