linux-kernel - Re: 4.3 group scheduling regression

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Message-ID: <20151013080648.GP3604@twins.programming.kicks-ass.net>
Date:	Tue, 13 Oct 2015 10:06:48 +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 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.
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