Re: FreeBSD is very slow when Memory chip sizes are imbalanced in slots

On Sun, Mar 17, 2013 at 8:26 PM, Mehmet Erol Sanliturk
<m.e.sanliturk_at_gmail.com> wrote:
> Dear All ,
>
> Previously , in the following message , I have mentioned effect of memory
> chip placement on execution speed :
>
> http://lists.freebsd.org/pipermail/freebsd-current/2012-February/031836.html
> Effect of Processor and Memory on KDE4 execution
> speed<http://lists.freebsd.org/pipermail/freebsd-current/2012-February/031836.html>

These seems to be more than different memory slot allocation between
those two boxes.

Can you reproduce this on the one labelled 'FAST' by assigning memory
in the same manner as it is assigned in the one labelled 'SLOW'?

>
>
> The above thread did not produce any usable result .
>
> The problem is persisting over 9.1 and 10.0 current .
>
> My opinion is that , it is NOT related to KDE only .
>
> After X is started , any desktop is behaving very slowly .
> This is also visible in PC-BSD and GhostBSD .

This is very nebulous. What is 'very slowly'? Is there a test you can
run that is independent of X, KDE, etc that demonstrates this?

One thing that KDE does require (iirc - from about 5 years ago,
probably wrong now) is that since KDE is C++, it spends a lot of time
loading executables/libraries into memory and prelinking them. If you
have dramatically lowered your RAM bandwidth, then this stage could
take a lot longer.

One thing that could cause memory bandwidth to lower is by installing
mismatched modules. The BIOS will set all RAM up at the same speed,
the lowest that all of the installed RAM supports. If you fill the RAM
slots with mismatched modules of different sizes, it may also not
enable dual channel memory, further reducing the RAM bandwidth.

Because of this, I think it is a jump to go from "My computer runs
slow when I put these bits of RAM in" to "FreeBSD always runs slow
when there is mismatched RAM".

If you find out what is slow on FreeBSD - eg RAM bandwidth -  you can
then test the same thing in Linux. If Linux shows the same slowdown
from fast to slow, then I'm sorry, that's a hardware defect. If, on
the other hand, Linux is just as fast in both configurations, then I'm
sure a lot of people would be interested as to why.

Cheers

Tom