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. > > > >> 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. > > Don't forget that not all drivers in the tree set the TSO limits before > if_attach(), so possibly the subtraction of one TSO fragment needs to go > into ip_output() .... > I don't really care where it gets subtracted, so long as it is subtracted at least by default, so all the drivers that don't subtract it get fixed.
However, I might argue that tcp_output() is the correct place, since tcp_output() is where the tcp/ip header mbuf is prepended to the list. The subtraction is just taking into account the mbuf that tcp_output() will be adding to the head of the list and it should count that in the "while()" loop. rick > --HPS > > _______________________________________________ > freebsd-...@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" > _______________________________________________ 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"
