Re: [PATCH 2.6.6-rc3-mm1] Add maxthinktime to sysfs

[Nick Piggin <nickpiggin@yahoo.com.au>]

FabF wrote:
> On Sat, 2004-05-01 at 00:42, Andrew Morton wrote:

>>Badari, did you find any need to vary this in the AS tuning work which you
>>were doing?  (What happened to that, btw?)
>>
>>If we're going to expose this tunable to users it needs to be documented in
>>as-iosched.txt
> 
> 
> I'm an absolute beginner Andrew ... Maybe someone more experienced could do that ?
> 

No no, writing end user documentation is much easier than writing
kernel code!

But either way you needn't worry about it because this isn't something
that you would want to tweak from userspace really. If you find it
useful to do some tuning then I guess it can go in -mm.

> PS:Attached the patch v2.
> 
> Best regards,
> Fabian
> 
> 
> ------------------------------------------------------------------------
> 
> ffbench 11 - Fabian Frederick 04/2004 - asio - maxthinktime - 10 clients
> 5	100	300
> ---------------------
> 5.37	21.26	16.28
> 11.71	23.10	20.14
> 15.22	21.05	20.20
> 13.85	18.03	17.55
> 11.58	16.39	16.86
...

maxthinktime of 5 is below the default antic_expire of 6. This
basically turns off the thinktime heuristic, so it isn't really
surprising that it runs like crap.

The *minimum* maxthinktime you should be playing with is probably
about double the antic_expire value.

Raising the value will make the heuristic a bit more restrictive
which could be a good idea. I think OSDL's STP has a couple of
database tests where the anticipatory scheduler has a small
regression (dbt2, dbt3). They might be helpful to you.