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SubjectRe: [PATCH 0/2] pdflush fix and enhancement
please CC me on replies, I am not subscribed to LKML.

----- Original Message ----
> From: Andi Kleen <>
> To: Peter W. Morreale <>
> Cc: Andi Kleen <>;
> Sent: Wednesday, December 31, 2008 3:46:09 AM
> Subject: Re: [PATCH 0/2] pdflush fix and enhancement


> > I actually think the question is: Why not allow the admin to control
> > this? Since it seems like this is a matter of policy based on machine
> > configuration.
> The kernel should know the current machine config and most
> admins don't really want to do very fine grained configuration;
> they expect the system to perform well out of the box. That is
> why it is adventageous to try to come up with good auto tuning.

Independent of the patch in question, the problem with this seems to me that [some/many of] the kernel developers [seem to] try to get it right for 100% of all thinkable use-cases. But this fails to take into account that:

- you cannot think of every single use-case. And not only because predicting furure use-cases is difficult
- getting it right for every case very often creates complexity that leads to subtle problems tha are hard to analyse and fix
- it may waste developer ressources
- and, think about it, do we really want the kernel to be smarter than ourselves ? :-)

You are right that the kernel should work out of the box most of the times. And it usually is pretty good at that. But there are corner-cases where more flexibility for the admins is desirable - if only to debug a problem without doing deep code hacking. So we should be careful adding tuning-knobs, but we should also admit that sometimes they are useful.

Happy New Year

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