linux-kernel - Re: [PATCH?] Livelock in pick_next_task_fair() / idle

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Message-ID: <1435824347.5351.18.camel@gmail.com>
Date:	Thu, 02 Jul 2015 10:05:47 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Rabin Vincent <rabin.vincent@...s.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH?] Livelock in pick_next_task_fair() / idle_balance()

On Thu, 2015-07-02 at 07:25 +0800, Yuyang Du wrote:

> That being said, it is also obvious to prevent the livelock from happening:
> idle pulling until the source rq's nr_running is 1, becuase otherwise we
> just avoid idleness by making another idleness.

Yeah, but that's just the symptom, not the disease.  Better for the idle
balance symptom may actually be to only pull one when idle balancing.
After all, the immediate goal is to find something better to do than
idle, not to achieve continual perfect (is the enemy of good) balance.

	-Mike

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