Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT
From: Peter Zijlstra
Date: Tue Sep 29 2015 - 11:10:41 EST
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)
> #define PREEMPT_DISABLED PREEMPT_ENABLED
> 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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