Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT
Date	2015-09-29 17:20 +0200
Message-ID	<qe4Rc-1Nk-35@gated-at.bofh.it> (permalink)
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On Tue, Sep 29, 2015 at 11:00:49AM -0400, Steven Rostedt wrote:
> 
> [ Resend, with the Cc list back ]

You seem to have a hard time with these buttons today ;-)

> 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?

Good point, PREEMPT_COUNT isn't required for voluntary preemption; when
I tested the voluntary build nothing bad happened, but that could have
been luck of course.

So what we can do is use an unconditional 1 for INIT_PREEMPT_COUNT, such
that the init task will have a raised preempt_count() during boot, even
on !PREEMPT_COUNT kernels.

But that means we cannot use INIT_PREEMPT_COUNT for
init_task_preempt_count() and such like, as I wanted to. I'll make
FORK_PREEMPT_COUNT for that instead.
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[RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT Peter Zijlstra <peterz@infradead.org> - 2015-09-29 11:50 +0200
  [tip:sched/core] sched/core: Simplify INIT_PREEMPT_COUNT tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2015-09-29 12:40 +0200
  Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT Frederic Weisbecker <fweisbec@gmail.com> - 2015-09-29 15:30 +0200
  Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT Steven Rostedt <rostedt@goodmis.org> - 2015-09-29 16:50 +0200
    Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT Peter Zijlstra <peterz@infradead.org> - 2015-09-29 17:00 +0200
  Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT Steven Rostedt <rostedt@goodmis.org> - 2015-09-29 17:10 +0200
    Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT Peter Zijlstra <peterz@infradead.org> - 2015-09-29 17:20 +0200

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