linux-kernel - Re: [PATCH 1/7] sched/fair: use reweight

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Message-ID: <20170731104538.2a7n3ovhyegryvy6@hirez.programming.kicks-ass.net>
Date:   Mon, 31 Jul 2017 12:45:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        umgwanakikbuti@...il.com, tj@...nel.org, kernel-team@...com,
        Josef Bacik <jbacik@...com>
Subject: Re: [PATCH 1/7] sched/fair: use reweight_entity to reweight tasks

On Fri, Jul 14, 2017 at 01:20:58PM +0000, Josef Bacik wrote:
> From: Josef Bacik <jbacik@...com>
> 
> reweight_task only accounts for the load average change in the cfs_rq, but
> doesn't account for the runnable_average change in the cfs_rq.  We need to do
> everything reweight_entity does, and then we just set our inv_weight
> appropriately.

The difference is in the calling convention. If you look at the
callsite:

	set_user_nice()
	  set_load_weight()
	    reweight_task()

You'll see that ->on_rq will always be false. That said, I think you're
right in that we're missing a se->runnable_weight update, because while
__update_load_avg*() doesn't use it (and will in fact (re)set it), there
are other users that could come before that.