HOWTONOT: upgrade memory

vermaden

vermaden

I add this little 'story' here as a warning, that may be helpful for performance troubleshooting.

Some time ago I bought used MINI ITX motherboard with Intel T8100 CPU and 965GM chipset, it came along with used 2 x 512MB RAM 667MHz DDR2. I already had 2 x 2GB RAM 800Mhz DDR2 from my older box, so the first thing I did after assembling all the parts was upgrade the amount of RAM.

The system worked well, 50+ days of uptime until power loss from time to time, it has ZFS mirror on 2 x 2TB drives. But I 'found' some strange performance problems.

So I started to look for the cause of the problem.

First I thought its slow because I have 80% filled ZFS, but after upgrade to 8.2-STABLE and various performance improvements it should not be a problem.

Then I thought that CPU may be overheating ... but it wasnt.

My 2TB disks are LOW POWER Seagate's so I thought that maybe their random access time is so low that its because of that, nope.

I also thought that it may be because of maybe broken 8GB CompactFlash card that is used for hte base system, nope.

At that point I did not had any clues what to check more.

But I thought, maybe I will also check memory ...

I found some nice simple memory allocation benchmark called ebizzy (nor in ports) and run # ebizzy -s 4096 to check the speed, compared with memory allocation speed on somparable laptop ... and VIOLA! Thats the problem.

I have just 'degraded' memory from 4GB 800MHz to 1GB 667Mhz and now allocations in ebizzy raised from 11462 records/s into whooping 2347823 recors/s :)

Also ffmpeg performance improved from 0.2 FPS into ... 40 FPS

Its because 965GM chipset maximum frequency is 667 MHz.

You have been warned ]:->
 
@OH

Thanks for input, but isnt 'uncacheable bug' related to the graphics driver? I ask because I do not even have x11 installed on that box.

I will try to put single 2GB stick into the box, that could confirm the bug theory.
 
Back in the day you could stick a PC133 DIMM in a PC100 machine without any issues. With todays multi-megahertz frequencies this doesn't seem to work reliably anymore. Best thing is to stick modules with the same frequency as the slot can handle. Faster memory in slower slots just doesn't work like it used to. Mixing memory speeds was (and still is) never a good idea.
 
@OH

Thanks mate, I will probably stick to 1-2GB on that box then, at least until I get something different, but that would have to wait until FreeBSD Foundation project on KMS/GEM integration finishes so I could get Core i3 2100T + MINIITX motherboard for example.
 
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