On 2 March 2016 at 05:50, David Gwynne <[email protected]> wrote: > the max_link hdr is basically how much space to reserve before an > ip packet for link headers, eg, ethernet. > > 16 bytes was a good choice when everything was just ip inside > ethernet, but now we deal with a bunch of encapsulations which blow > that out of the water. 16 bytes isnt even enough if we have to > inject a vlan tag ourselves. > > im suggesting 64 because it will comfortably allow you to encap an > ethernet header inside of an ip protocol. i think it is even enough > to accomodate vxlan overhead. > > the caveat to this is that it changes the watermark for what is the > smallest packet that can go into an mbuf. currently the space in > an mbuf with headers is about 184 bytes. with a max_linkhdr of 16 > that would allow a 168 byte ip packet. after this you can put a 120 > byte packet in. > > however, most ip packets are either small (think keystrokes over > ssh, ACKs, or dns lookups) or full sized (always greater than MHLEN > anyway). this change therefore has minimal impact on the majority > of traffic, except to make prepending encap headers a lot cheaper. > > ok? >
I'm fine with the change, but why are you replicating the XXX comment? Why is it there? Is it a wrong place to put it?
