On Tue, 2013-05-14 at 09:32 +0100, David Laight wrote: > > The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > > (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no > > need for this optimisation any more. > > Hmmm.... even on x86 there will be a measurable cost > in misaligned accesses - at least for some workloads. When they cross cache-line boundaries, yes. Maybe napi_get_frags() should be adding the 2 byte offset on all architectures, as the skbs it allocates are never RX DMA buffers. > If the DMA is able to write to a mis-aligned buffer and > still perform aligned burst transfers mid-frame then > 4n+2 aligning the rx buffer should be a win even on x86. I don't think so. > Note to hardware engineers: add an option to write two > bytes of junk before the rx data :-) There is some hardware with that option. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
