linux-kernel - Re: [PATCH 7/8] sched: non-zero lag renice

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Message-ID: <49020A2A.5070809@nortel.com>
Date:	Fri, 24 Oct 2008 11:47:22 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, efault@....de,
	vatsa@...ibm.com
Subject: Re: [PATCH 7/8] sched: non-zero lag renice

Peter Zijlstra wrote:

 > Then renicing, esp when lowering nice value (getting heavier), its possible
 > to get into a starvation scenario. If you got too much runtime as a very
 > light task, you get shot way far too the right, which means you'll have to
 > wait for a long time in order to run again.
 >
 > If during that wait you get reniced down, fairness would suggest you get run
 > earlier, because you deserve more time.
 >
 > This can be solved by scaling the vruntime so that we keep the real-time
 > lag invariant.

If we've already been shot way out to the right, presumably that would give us 
a large real-time lag.  If we renice to a lower nice level, wouldn't we want 
to reduce the real-time lag rather than make it constant?

Chris
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