> > It's an Alpha with 768 MB. Is it the pci_alloc_* functions you are
> > referring to? I don't think they are used currently. How much memory
> > can these allocate? I need chunks of up to 1 MB, not necessarily
> > phycically continuous.
> >
> > What do those functions do that normal memory allocation does not?
> > Apart from setting up sg mappings, that is.
>
> A normal memory allocation might not be visible from the device, however
> pci_map_sg() deals with such things. What I really meant was are you
> using the pci_ DMA functionality
Those functions are not used at the moment, but I could change that.
The question remains why DMA transfers are so slow. The memory is
clearly visible from the bus.
Btw, I just noticed that hard disk throughput is much lower with 2.5
than 2.4. With 2.4.21-pre5 I get ~40 MB/s, but with 2.5.67 the speed
drops to 25-30 MB/s. Everything according to hdparm. Is it possible
that DMA is generally slow for some reason?
-- Måns Rullgård mru@users.sf.net - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/