On Mon, Apr 21, 2008 at 01:16:23AM -0700, David Miller wrote:

What's being discussed is having the top of the transmit call path
getting a socket "buffer" pointer, that it can feed back into the
packet input path directly.  Loopback would return buffer pointers
from ->hard_start_xmit() instead of passing them netif_rx().  The top
of the transmit call path, upon getting a non-NULL buffer returned,
would pass it to netif_receive_skb().

Yes this will definitely reduce the per-packet cost.  The other
low-hanging fruit is to raise the loopback MTU to just below 64K.
I belive the current value is a legacy from the days when we didn't
support skb page frags so everything had to be physically contiguous.

Longer term we could look at generating packets > 64K on lo, for
IPv6 anyway.

Cheers,
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