On Wed, Aug 19, 2015 at 09:51:44AM +0200, Hans Petter Selasky wrote: > On 08/19/15 09:42, Yonghyeon PYUN wrote: > >On Wed, Aug 19, 2015 at 09:00:52AM +0200, Hans Petter Selasky wrote: > >>On 08/18/15 23:54, Rick Macklem wrote: > >>>Ouch! Yes, I now see that the code that counts the # of mbufs is before > >>>the > >>>code that adds the tcp/ip header mbuf. > >>> > >>>In my opinion, this should be fixed by setting if_hw_tsomaxsegcount to > >>>whatever > >>>the driver provides - 1. It is not the driver's responsibility to know if > >>>a tcp/ip > >>>header mbuf will be added and is a lot less confusing that expecting the > >>>driver > >>>author to know to subtract one. (I had mistakenly thought that > >>>tcp_output() had > >>>added the tc/ip header mbuf before the loop that counts mbufs in the > >>>list. > >>>Btw, > >>>this tcp/ip header mbuf also has leading space for the MAC layer header.) > >>> > >> > >>Hi Rick, > >> > >>Your question is good. With the Mellanox hardware we have separate > >>so-called inline data space for the TCP/IP headers, so if the TCP stack > >>subtracts something, then we would need to add something to the limit, > >>because then the scatter gather list is only used for the data part. > >> > > > >I think all drivers in tree don't subtract 1 for > >if_hw_tsomaxsegcount. Probably touching Mellanox driver would be > >simpler than fixing all other drivers in tree. > > Hi, > > If you change the behaviour don't forget to update and/or add comments > describing it. Maybe the amount of subtraction could be defined by some > macro? Then drivers which inline the headers can subtract it? >
I'm also ok with your suggestion. > Your suggestion is fine by me. > > The initial TSO limits were tried to be preserved, and I believe that > TSO limits never accounted for IP/TCP/ETHERNET/VLAN headers! > I guess FreeBSD used to follow MS LSOv1 specification with minor exception in pseudo checksum computation. If I recall correctly the specification says upper stack can generate up to IP_MAXPACKET sized packet. Other L2 headers like ethernet/vlan header size is not included in the packet and it's drivers responsibility to allocate additional DMA buffers/segments for L2 headers. > > > >>Maybe it can be controlled by some kind of flag, if all the three TSO > >>limits should include the TCP/IP/ethernet headers too. I'm pretty sure > >>we want both versions. > >> > > > >Hmm, I'm afraid it's already complex. Drivers have to tell almost > >the same information to both bus_dma(9) and network stack. > > You're right it's complicated. Not sure if bus_dma can provide an API > for this though. > > --HPS _______________________________________________ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"