linux-kernel - Re: [RFC][PATCH 00/18] Increase resolution of load weights

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Date:	Thu, 21 Apr 2011 18:40:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nikhil Rao <ncrao@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 00/18] Increase resolution of load weights

On Wed, 2011-04-20 at 13:51 -0700, Nikhil Rao wrote:
> 
> I would like to get some feedback on the direction of this patchset. Please let
> me know if there are alternative ways of doing this, and I'll be happy to
> explore them as well.
> 
> The patchset applies cleanly to v2.6.39-rc4. It compiles for i386 and boots on
> x86_64. Beyond the basic checks, it has not been well tested yet.
> 
> Major TODOs:
> - Detect overflow in update shares calculations (time * load), and set load_avg
>   to maximum possible value (~0ULL).
> - tg->task_weight uses an atomic which needs to be updates to 64-bit on 32-bit
>   machines. Might need to add a lock to protect this instead of atomic ops.
> - Check wake-affine math and effective load calculations for overflows.
> - Needs more testing and need to ensure fairness/balancing is not broken.

The code looks fairly ok and I can't fault the TODOs ;-)

I guess getting some measurements on the performance penalty on 32bit
would be nice -- if only to know about how bad it is.

And while its not perfect by a long stretch (we can still blow the whole
lot by creating a deep enough hierarchy) it should be much better.. the
only advantage of going with a full on wrapper solution would be that
plugging in an arbitrary precision type would be simple ;-)

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