Tuesday, November 22, 2005

Of DMA and southbridges....

After getting a new motherboard, Linux seemed to be running fine except that I kept getting this message on boot up:
VP_IDE: Unknown VIA SouthBridge, contact Vojtech Pavlik < vojtech@ucw.cz >

Later on, I realized that my CPU was being used every time I read/wrote anything to Disk. This CPU usage was very evident when I decided to burn a CD. It took up nearly 60% of my CPU time! Considering that this used to be about 5% on my older CPU,it is a 15 times increase over the previous value. This led me to believe that somehow the kernel has disabled the DMA, and all the reads/writes are being routed through the CPU.

I was wondering whether DMA is controlled by the north or south bridge of the computer, and I tried asking a few of my friends, but they were as clueless as me. I immediately opened my crappy text-book to see if they had any clues, but there were none :-( However, I did notice that the ATA/SATA connections go into the Southbridge(SB), and the SB is not directly connected to the CPU, but is to the NB. Wow! This made me believe that DMA is controlled by the SB. To confirm, a quick search on google revealed the following:


Which proved that I was right!

So much for that ;-)
Now it only remains to get a new kernel:d

1 comment:

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