Hi again,

Roman Zippel wrote:

quoted

On another interesting note: The raw devices I'm writing to are Fibre
Channel drives controlled by a Qlogic 2200 adapter (in 2.2.14 I'm using
the Qlogic driver). When writing large sequential blocks to a single
drive, I reached 8MB/s when the memory was mapped to the high reserved
region, while CPU utilization was down to about 5%. When the mapping was
to PCI space, I was able to write at only 4MB/s, and CPU utilization was
up to 60%!

The data is copied from a buffer to the pci device. DMA transfers going
directly to pci space is impossible without (small) changes to 2.2. 2.4
has the theoretic possibility to do it and checks already for that, but
how it should be done practically I'd like to know too.

Okay - if you're right, then this explains the poor performance I'm
seeing for PCI-PCI raw I/O on 2.2.14... Raw I/O is senseless if bounce
buffers are used. Still, raw I/O (the kiobuf stuff) seems to be quite
broken on 2.4.0t3...

-Mark
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