> >
> > In my network configuration this approach seems like I could potentially
> > save myself a few CPU cycles by not having to fill the Ethernet header
> each
> > time I want to transmit (so long as I know where it needs to go). Is
> > scatter-gather doable with RTNet?
> >
>
> At least it's mentioned here:
>
> <<http://www.rts.uni-hannover.de/rtnet/download/Dev04_API-Tutorial.pdf>>
>
> I use the same card, so can you post your findings to the list?
>
> Bernhard
I spent some time last night looking at this. It looks like RTNet
implements an iovec structure that is very similar to the one in the Linux
kernel. From what I've seen so far though it is only used on the receive
side. There is actually an example of it being used on the receive side:
rtnet/examples/xenomai/posix/rtt-[sender/responder].c. I haven't yet
determined if it is supported on the transmit side. Linux supports the
functions readv() and writev(); these functions don't exist in the RTNet
stack. I suspect calling the regular Linux readv() and writev() won't
work?? Or, isn't want I want?
Also, it looks as though the iovec in RTNet is only used for IP packets. In
my case I am trying to use it for Ethernet frames. I'm not sure what that
means for me.. To be honest, it seems in order to get any real benefit out
of scatter gather (for transmitting), I would think that functionality would
have to be some how supported by the NIC hardware/driver. Is this true?
Otherwise when the driver goes to transmit I would think it would have to
memcpy() the buffers into one contiguous buffer, then transmit. If thats
the case then I don't gain much in the way of performance.
Anyone have any thoughts on this that would help demystify some of scatter
gather and RTNet?
-Rob
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