Messages in this thread | | | Subject | Re: DMA transfers in 2.5.67 | From | (Måns Rullgård) | Date | 16 Apr 2003 00:09:00 +0200 |
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Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
> > 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/
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