Re: The Kernel (fwd)

[George Bonser <grep@oriole.sbay.org>]

On 25 Jan 1998 jfm2@club-internet.fr wrote:

> 1) Bogomips have nothing to do with our problem: we are speaking of
> memory usage.  That is related with _SWAPPING_.  By reducing kernel
> size you will make your machine faster when short of memory because
> you will have lesser swapping.

I doubt it ... how much swapping do think is going on anyway? Besides, if
we take out 200K or even 500k (I seriously doubt it would be that high but
for the sake of the discussion ... ok).  Look at your system ... how much
do you have swapped out now.  What processes are they?  Chances are those
are getty processes on unused VT's that have been swapped out.  The fact
is that on a system of >32MB, there is just not a whole lot of swapping
going on and once you start a really big program running, that 500k is not
going to make any difference because you are probably short more than that
anyhow.

Look at it this way.  Removing those drivers gives exactly the same
performance boost of adding 2 256k simms. (Provided that you can get 500k
out of there but I doubt it).  How much performance gain do you get from
adding 1/2Meg of RAM?  If you have 4MEG, you probably get a lot.  If you
have 32MEG, you will probably never notice it.

That is what I am getting at.  If you can document a significant
performance boost, that would be worth considering. I am just skeptical of
ACTUAL performance boost gained from this as opposed to problems.

Have you asked the Debian kernel maintainer why those were left in there
... nevermind, I will do it.  For all I know, they MIGHT have tried this
but run into problems. 

There is a THEORETICAL performance boost IF you are constantly thrashing
things in and out of swap that are smaller than 500k in size. Once you
start swapping more than this in and out of RAM (A 4MB news history file
for example) that 1/2MEG is meaningless.

> 2) Adding RAM or reducing the kernel size will have ZERO effect if all
> your processes fitted in memory.

Correct, so until you get to the point of swapping, there is no
performance gain.  You DO gain performance in the range between the time
you start swapping up until you reach a point where you are swapping out
>500k. At that point performance is again identical to the non-stripped
kernel.

8MB SIMMS are $12 here.  For $24 you get a 32 times performance boost than
stripping the SCSI drivers out of the kernel.

> 
> 3) Bogomips is NOT a speed test, it is a CALIBRATION test.  Its goal
> is to allow some drivers to measure time when precision is critical.

RIght, it is a timed countdown loop. What I was getting at is that UNTIL
you start swapping there is no performance increase.  What I have said
here is that you DO gain performance as long as you are swapping out <1/2
Meg. Once you go more than that, the performance gain again evaporates. 



George Bonser 
If NT is the answer, you didn't understand the question. (NOTE: Stolen sig)
http://www.debian.org
Debian/GNU Linux ... the maintainable operating system.