[nSLUG] performance and schedulers

Donald Teed donald.teed at gmail.com
Wed Jun 22 09:12:32 ADT 2005

I have reached my own conclusions:

1. Alan Cox says the IDE drivers are a mess. This man is one of
the original core Linux developers. I hear him, and I see the
performance numbers of me and many other user on the 'net.
I'm sticking with 2.4 kernel for the time being. If you are using
SCSI, this might not apply.

2. Everyone has been getting 2.6 kernels with all of the IO Schedulers
built into the kernel. You just have not been able to deselect them
or see the schedulers from the menuconfig option to the kernel's make
(until 2.6.12 or thereabouts). The only way you can actually use
a scheduler other than the default anticipatory one is to set 
the elevator= kernel option in your lilo or grub config.

3. The 2.6 kernel isn't necessarily the best performer for you.
Take a look at this benchmarking article:
An analogy might describe this: 2.6 kernel is like a car that
will still do at least 10 mph in a traffic jam, while 2.4 is stopped,
but the 2.6 kernel tops out at 60 mph, while 2.4 can do 80
(in the case of IDE drives anyway).

On 6/22/05, Jim Haliburton <jim at on-site.ns.ca> wrote:
> Good Day all:
> I have read the various items on schedulers and performance and have 
> several
> questions.
> 1) With a careful test of each of the various schedulers and their tunable
> paramters, how much performance gain could one expect? Are we talking 10. 
> 15
> or 30% change?
> 2) Would a selection of higher performance components in the system give 
> you a
> quicker and cheaper performance gain? In other words is it more productive 
> to
> just go buy a bigger box? I am more hardware oriented and find that well
> matched components often give much better performance gain, than hours 
> spent
> tweaking the OS. Thoughts??
> 3) What do you do when the app(s) running on the box or the storage needs 
> of
> the app changes? Do you have to go through the tweaking process all over
> again?
> 4) Are there guidelines to use if application characteristics are known?
> 5) Are there any automatic tuning apps that can run in the background and
> monitor the various loads and then recommend a recomplie with different
> options? I know there used to be such a tool for SCO that if left running 
> for
> a week or so would recommend changes. In one case the performance gain was
> truly dramatic.
> Regards
> Jim H
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> nSLUG at nslug.ns.ca
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