linux-kernel - Re: 4.3 group scheduling regression

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Message-ID: <20151013081023.GO11639@twins.programming.kicks-ass.net>
Date:	Tue, 13 Oct 2015 10:10:23 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: 4.3 group scheduling regression

On Tue, Oct 13, 2015 at 10:06:48AM +0200, Peter Zijlstra wrote:
> On Tue, Oct 13, 2015 at 03:55:17AM +0800, Yuyang Du wrote:
> 
> > I think maybe the real disease is the tg->load_avg is not updated in time.
> > I.e., it is after migrate, the source cfs_rq does not decrease its contribution
> > to the parent's tg->load_avg fast enough.
> 
> No, using the load_avg for shares calculation seems wrong; that would
> mean we'd first have to ramp up the avg before you react.
> 
> You want to react quickly to actual load changes, esp. going up.
> 
> We use the avg to guess the global group load, since that's the best
> compromise we have, but locally it doesn't make sense to use the avg if
> we have the actual values.

That is, can you send the original patch with a Changelog etc.. so that
I can press 'A' :-)
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