Re: PCI DMA to small buffers on cache-incoherent arch

From: Benjamin Herrenschmidt (benh@kernel.crashing.org)
Date: Tue Jun 11 2002 - 12:33:47 EST


>Remember please that specifically the DMA mapping APIs encourage use
>of consistent memory for small data objects. It is specifically
>because non-consistent DMA accesses to small bits are going to be very
>slow (ie. the PCI controller is going to prefetch further cache lines
>for no reason, for example). The non-consistent end of the APIs is
>meant for long contiguous buffers, not small chunks.
>
>This is one of the reasons I want to fix this by making people use
>either consistent memory or PCI pools (which is consistent memory
>too).

Please don't limit the API design to PCI ;)

There are more and more embedded CPUs out there with their own
bunch of on-chip devices that are neither consistent nor PCI based,
their drivers will have the exact same problem to deal with though.

Ben.

-
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/



This archive was generated by hypermail 2b29 : Sat Jun 15 2002 - 22:00:25 EST