linux-kernel - Re: [PATCH] sched: balance_cpu to consider other cpus in its group as target of (pinned) task migration

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Date:	Mon, 04 Jun 2012 14:47:43 +0200
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Prashanth Nageshappa <prashanth@...ux.vnet.ibm.com>,
	mingo@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	roland@...nel.org, Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: balance_cpu to consider other cpus in its group
 as target of (pinned) task migration

On Mon, 2012-06-04 at 13:53 +0200, Peter Zijlstra wrote: 
> On Mon, 2012-06-04 at 11:25 +0200, Mike Galbraith wrote:
> > Isn't this poking the wrong spot?
> 
> Yes and no, the use-case is definitely so-so.. However, even if a FIFO
> task were to only consume 95% of time, we might still want to balance
> things differently, and I don't think we do the sane thing there either.

You need a good reason to run RT, and being able to starve others to
death ain't it, so I don't see a good reason to care about the 95% case
enough to fiddle with load balancing to accommodate the oddball case.

Agreed it is a hole, but it's one dug by root.  If you need so much CPU
that you can and will starve SCHED_OTHER to death, you need isolation
from SCHED_OTHER, lest they do evil things to your deadline, just as
much as they desperately need protection from your evil CPU usage ;-)

-Mike

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