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

On Mon, Mar 18, 2013 at 3:01 AM, Tom Evans <tevans.uk_at_googlemail.com> wrote:

> 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
>

I think , all of the answers to your questions may be found in the above
referenced thread messages :

 Every possible combination has been tried , and identified that the
problem is different memory chip sizes for FreeBSD ( v9.0 , v9.1 , v10.0 )
( GhostBSD , PC-BSD , v9.0 , v9.1 ) :

Channel A : Slot 1 : 2 GB
                  Slot 2 : 1 GB


Channel B : Slot 1 : 2 GB
                  Slot 2 : 1 GB


All of the memory chips : Kingston HyperX , same  clock frequency .
Memory placement kind is correct .

There is NO any hardware defect .

Linux is insensitive to such different memory chip sizes ( I am using
Fedora , CentOS , Mandriva , Mageia , OpenSUSE , Arch Linux , Puppy Linux ,
and some others ... )

Thank you very much .

Mehmet Erol Sanliturk