Re: [RFC v3 1/6] Track the active utilisation

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC v3 1/6] Track the active utilisation
Date	2016-11-18 15:30 +0100
Message-ID	<sESkX-8jW-53@gated-at.bofh.it> (permalink)
References	<svO6S-ak-7@gated-at.bofh.it> <svO6S-ak-23@gated-at.bofh.it> <sw63L-3ER-11@gated-at.bofh.it> <sw6dr-3Ia-17@gated-at.bofh.it> <swaqJ-6ln-21@gated-at.bofh.it>
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On Tue, Oct 25, 2016 at 09:58:11AM -0400, Steven Rostedt wrote:

> I agree with Daniel, especially since I don't usually trust the
> compiler. And the added variable is more of a distraction as it doesn't
> seem to have any real purpose.

I don't think there's anything here to trust the compiler on. Either
it inlines or it doesn't, it should generate 'correct' code either way.

If it doesn't inline, its a dumb compiler and it will make these dumb
decisions throughout the tree and your kernel will be slow, not my
problem really ;-)

That said, I agree that the single line thing is actually easier to
read.

That said; there's something to be said for:

	u64 running_bw;

static void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
	u64 old = dl_rq->running_bw;

	dl_rq->running_bw += dl_se->dl_bw;
	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
}

static void sub_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
	u64 old = dl_rq->running_bw;

	dl_rq->running_bw -= dl_se->dl_bw;
	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
}

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Re: [RFC v3 1/6] Track the active utilisation Peter Zijlstra <peterz@infradead.org> - 2016-11-18 15:30 +0100
  Re: [RFC v3 1/6] Track the active utilisation luca abeni <luca.abeni@unitn.it> - 2016-11-18 16:20 +0100
    Re: [RFC v3 1/6] Track the active utilisation Peter Zijlstra <peterz@infradead.org> - 2016-11-18 16:30 +0100
  Re: [RFC v3 1/6] Track the active utilisation Steven Rostedt <rostedt@goodmis.org> - 2016-11-18 17:50 +0100

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