linux-kernel - Re: [PATCH] sched/fair: Do not decay new task load on first enqueue

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Date:   Wed, 19 Oct 2016 11:53:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Matt Fleming <matt@...eblueprint.co.uk>,
        Wanpeng Li <kernellwp@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Yuyang Du <yuyang.du@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH] sched/fair: Do not decay new task load on first enqueue

On Wed, Oct 19, 2016 at 08:38:12AM +0200, Vincent Guittot wrote:
> > It might make sense to have helper functions to evaluate those
> 
> The main issue is the number of parameters used in these conditions
> that makes helper function not really more readable.

Fair enough I suppose..

> > conditions, because currently there's two instances of each, once in the
> > branch selection and then again (but inverted, we miss the == case fwiw)
> 
> not sure to catch the comment about inverted and miss the == case

Oh, you're right. Which proves my point on this not being entirely
readable :/

Initially I thought the things were of the form:

	else if (ineq) {
	}

	...

	if (... || !ineq || ...)


Which would get you things like: a<b, !a<b := a>b, and leave a==b
undefined. But if I put them along side one another like:


+		} else if (min_runnable_load > (runnable_load + imbalance)) {

+	                  (min_runnable_load > (this_runnable_load + imbalance)) ||


+		} else if ((runnable_load < (min_runnable_load + imbalance)) &&
+				(100*min_avg_load > sd->imbalance_pct*avg_load)) {

+	             ((this_runnable_load < (min_runnable_load + imbalance)) &&
+			        (100*min_avg_load > sd->imbalance_pct*this_avg_load)))

We can see this is not in fact the case.

Blergh, I also cannot see a pretty way to increase readability here,
because while they have the same general shape, there's this small
variation with this_*.

A well..