>IOAT DMA offloading works for TCP only. It does not support UDP. >Only large buffers are offloaded to DMA engine (> 4kB). >DCA is a different feature that supports endpoint device to >memory writes and it works regardless of transfer size.
Maciej, It seems to me that with the 5400 chipset, the original I/OAT hardware interface has gone away. The 'ioatdma.ko' device driver depends on 'dca.ko', so it likely is a situation where the I/OAT API is still presented to the kernel but the underlying mechanism is DCA. The 4KB size can be adjusted downward with the 'net.ipv4.tcp_dma_copybreak' 'sysctl' parameter--I've set it to zero bytes. I've seen some Kernel.org messages which indicate that UPD will eventually be supported. The real point of my question is how effective the new DCA mechanism will be at mitigating CPU for small packets. Of course the device-to-memory aspect of DCA looks promising, but I'm starting to wonder if it really makes any significant difference. David ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ E1000-devel mailing list E1000-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/e1000-devel
