[TriLUG] Kernel slowdown

[Tanner Lovelace]

On Tue, 2002-01-01 at 22:09, Scott wrote:
> These quick and dirty tests seem to point to several possible reasons 
> for a slow down: 1) The stock RedHat kernel has several patches in it 
> that are streamlined specifically for the RedHat distro (if so, what 
> are they) 

Just about every distribution (i.e. I don't know any who don't) 
significantly patch their kernels.  Yesterday, I just had an interesting
time compiling a mandrake kernel with all the mandrake patches, 
and updating from 2.4.16 (with those patches!) *and* adding
the preemption patch.  The mandrake kernel I was using (straight
from the mandrake cooker (similar to redhat rawhide) applies
109 patches to the kernel.  It was applying everything from
the 2.4.17rc1 patch, to patches for XFS and JFS filesystems, to
updated drivers, etc...  Just to compare, while writing this
e-mail I downloaded the latest kernel from Redhat's Rawhide.
Redhat, in the 2.4.16 kernel applies 111 patches (including
the aforementioned 2.4.17rc1 patch).  

I've heard lots of people say the first thing they do after
an installation is compile a new kernel.  Well, it doesn't
seem like that's all that good an idea anymore.  If your distribution
assumes the kernel contains something that has been added
(i.e. I use the XFS filesystem which is not in the stock
kernel) and the new kernel you compile by hand doesn't have it,
the results can be disastrous.  I would suggest that this
is indeed the most likely answer to your question.

> 2) I've compiled in something to both the 2.4.17 kernels that 
> really slows down my machine (if so, what could that be) 3) It's the 
> fact that I'm using a strictly monolithic kernel while 2.4.7-10 is 
> modular (I thought modules slowed things down, not the other way 
> around) 4) 2.4.17 sucks (it's Linux, how could that be?)
[...]
> So here comes the question section: 1) Has anyone else noticed this? 2) 
> What could cause it?  3) How could I fix it?  4) What is the airspeed 
> velocity of an unladened swallow?
> 
1. No, but I tend to use the stock kernels, or at least add my
   patches directly to them rather than starting from scratch.
2. See explanation above.
3. Modify the redhat kernel .spec file.  Note that the default
   kernel .spec file compiles several different kernels.  It
   does, however, give you several macros that let you determine  
   exactly which kernels get compiled.  So, if you only need
   a uni-processor kernel, it will just compile it and not
   also compile an smp kernel, an bigmem kernel, a uml kernel,
   etc...
4. African or European?   (Aaahhhhh!!!!! :-D)

What are some other people's views on this?  Who uses stock 
kernels and who compiles their own?  If you compile your
own, what distribution do you use and have you noticed any
problems?  Hmm... this sounds like it would make an interesting
survey...

Tanner
-- 
Tanner Lovelace | lovelace at wayfarer.org | http://wtl.wayfarer.org/
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