linux-kernel - Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT

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Message-ID: <20150929110049.7b9de3eb@gandalf.local.home>
Date:	Tue, 29 Sep 2015 11:00:49 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	fweisbec@...il.com, oleg@...hat.com, umgwanakikbuti@...il.com,
	tglx@...utronix.de
Subject: Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT


[ Resend, with the Cc list back ]

On Tue, 29 Sep 2015 16:35:59 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Sep 29, 2015 at 10:37:29AM -0400, Steven Rostedt wrote:
> > On Tue, 29 Sep 2015 11:28:26 +0200
> > Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > As per commit d86ee4809d03 ("sched: optimize cond_resched()") we need
> > > PREEMPT_ACTIVE to avoid cond_resched() from working before the
> > > scheduler is setup.
> > > 
> > > However, keeping preemption disabled should do the same thing already,
> > > making the PREEMPT_ACTIVE part entirely redundant.
> > 
> > Thus PREEMPT_ACTIVE wasn't needed at that commit either, or was it?
> 
> Correct. We might have actually discussed that at that time but decided
> to be conservative -- but these be vague memories..

Hmm, I just looked closer and I'm wondering if this still works?

We have:

#ifdef CONFIG_PREEMPT_COUNT
#define PREEMPT_DISABLED	(1 + PREEMPT_ENABLED)
#else
#define PREEMPT_DISABLED	PREEMPT_ENABLED
#endif

Now if we just remove the PREEMPT_ACTIVE from the INIT_PREEMPT_COUNT,
when CONFIG_PREEMPT_COUNT is not set, wouldn't a _cond_resched() in
boot up schedule?

-- Steve
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