[conspire] DMA for SATA? -was: SATA HD transfers slow?
Luke S Crawford
lsc at prgmr.com
Mon Jul 26 01:38:59 PDT 2010
Mark S Bilk <mark at cosmicpenguin.com> writes:
> But every SATA transfer is still using up one of my two CPU cores.
> See the attached jpg of the KDE4 System Monitor, also downloadable
> here: http://cosmicpenguin.com/tmp/SysMon.jpg
> The wide peak is the transfer, and the narrow ones about every
> second are Firefox.
Is the red line IOWAIT?
> Here are copies of the CPU line from "top". The numbers add up
> to 100%, so the measurements for both cores are being added
> together. The transfer is using 30-45% wa (wait?) and 4 or 8%
> system (for disk-disk or disk-/dev/null). Added and multiplied
> by 2 these equal about 100% of one of the cores. Each transfer
> is a 700+MB file. I used a new one each time so it wouldn't be
> in disk cache.
IOwait doesn't mean you are using pio... look in dmesg. Iowait just
means "the cpu would have been running, but instead it was waiting for
I/O to complete" - so if you have a slow disk, you will get lots of
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