linux-kernel - Re: [PATCH] sched: Transform resched_task() into resched

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Date:	Sun, 29 Jun 2014 12:54:57 +0200
From:	Andreas Mohr <andi@...as.de>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	Andreas Mohr <andi@...as.de>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, mingo@...hat.com
Subject: Re: [PATCH] sched: Transform resched_task() into resched_curr()

On Sun, Jun 29, 2014 at 12:59:41PM +0400, Kirill Tkhai wrote:
> On 29.06.2014 12:36, Andreas Mohr wrote:
> > I just noticed that there is a part touching rq->idle,
> > and ISTR that idle task handling is "special"
> > (after all that's the power management side of things).
> > Specifically, rq->curr and rq->idle are distinct rq members
> > (since they are distinct tasks AFAIK!),
> > so there might now be some issues with task state tracking here
> > (unless this cleanup happens to unify handling here anyway).
> 
> Are you worrying about check_preempt_curr_idle()? I've looked
> at check_preempt_curr() and found, we never call this function
> in current scheduler logic.

Yeah - I should have included that hunk verbatim, sorry.

> It's called only if just enqueued task is of the same class as
> rq's current, but we can't have two idle class tasks enqueued
> on the same rq. So, it's just a stub. We can do not worry
> about this.

That seems to be the case indeed in current implementation.

Removing specific references from these sched_class parts
(here: idle_task.c, rq->idle) where possible seems to be a good direction,
since AFAIUI sched_class things are supposed to encode *behaviour*,
where containing too many specific-member references is best avoided.

I'd fathom that for the sched_curr() handler
I'm still somewhat in favour of an extra non-inline wrapper though;
it's just good minimal-dependency implementation.
But more frequent topic partners might have more valuable input
on this patch :)

Thanks,

Andreas
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