netmap custom RSS and custom packet info

[Luigi Rizzo]

On Mon, Jun 29, 2015 at 5:17 PM, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:

> Working with netmap and modern hardware I am lacking some features:
>
> a) some spare space before packet (64/128/192/256 bytes) for
> application data. For example: application do some pre-analysig
> packet, filled structure in this space and routed packet (via NETMAP
> pipe) to other thread. Received thread got packet and linked
> inforamtion about this packet for processing w/o additional overhead.
>

​spare space in front of the packet is something we have
been considering for a different purpose, namely better
support for encapsulation/decapsulation and things like
vhost-net header.

​Note though that the annotation is transferred for free
only in the case of pipes or ports sharing the same memory
region; vale ports would have to explicitly copy the
extra​ bytes which is (moderately) expensive.

A quick and dirty way to support what you want is the following:
- in the kernel code, modify NMB(), PNMB() and the offset between
  the netmap_ring and the first buffer to add the extra space
  you want in front of the packet. You can possibly make this
  offset a sysctl-controlled value

- in netmap_vale.c, make a small change to the code that copies
  buffers so that it includes also the space before the actual packet.

That should be all.



> b) custom RSS. Modern NIC have RSS poorly interoperable with packet
> analysing: packets from same flow, but different direction placed in
> different queue, PPPoE encapsulated packets placed in queue 0,
> different tunneling don't recognised and etc. May be NETMAP can be
> used custom RSS hashing from loadable kernel module, provideng by
> user? Function frm this module can be packet analysing, tunnel
> removing, custom RSS hashnig with direction-independly maner, filled
> some structure prepended to buffer (see above) and pass this
> information to application.
>

​RSS is completely orthogonal to​

​ netmap and I strongly
suggest to keep it this way, using either use the NIC-specific
tools to control RSS or some generic mechanism
(on linux there is ethtool, and we should implement something
similar also on freebsd).

​cheers
luigi
​


> This is possible? This is useful not only to me?
>
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