Hans Petter Selasky wrote: > On 09/13/14 22:35, Hans Petter Selasky wrote: > > > > I see the default set to (65536 - 4). I don't know why you > > subtracted 4 > > but I would have expected the max ethernet header length to be > > subtracted > > here? > > You mean to say that the default should be > > 65535 - ethernet header - vlan header ? > Almost. It is actually: 65536 - ethernet header - vlan header (or the min of IP_MAXPACKET vs 32*MCLBYTES - ethernet header - vlan header if you want to cover your butt for the case where the value of MCLBYTES is changed) IP_MAXPACKET (65535) comes from the fact that some devices use the iplen field of the ip header in the TSO segment for its length, I think? (Some do not and can support TSO segments greater than IP_MAXPACKET in length, but again, the default shouldn't assume this nor should it assume the device does the vlan header in hardware --> "- vlan header" to be safe for default.)
This is because there are lots of broken drivers (basically any one that has a limit of 32 transmit segments) and this at least makes them work correctly. Unfortunately they still do a lot of m_defrag() calls for this case, but with a patch like yours, the drivers may eventually get patched to use the max_frags setting and then avoid the need to do m_defrag() calls. rick > --HPS > > _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"