Date: Tue, 29 Apr 2008 09:17:17 -0700 From: Sam Leffler <sam@freebsd.org> To: Yehonatan Yossef <yoniy@mellanox.co.il> Cc: Tom Judge <tom@tomjudge.com>, freebsd-net@freebsd.org, Liran Liss <liranl@mellanox.co.il>, freebsd-questions@freebsd.org, Mr Y <yonyossef.lists@gmail.com> Subject: Re: OS throws away large packets Message-ID: <48174A0D.1090302@freebsd.org> In-Reply-To: <6C2C79E72C305246B504CBA17B5500C903E6C3B1@mtlexch01.mtl.com> References: <6C2C79E72C305246B504CBA17B5500C903E6C3B1@mtlexch01.mtl.com>
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Yehonatan Yossef wrote: > > > >> -----Original Message----- >> From: Tom Judge [mailto:tom@tomjudge.com] >> Sent: Monday, April 28, 2008 8:21 PM >> To: Mr Y >> Cc: freebsd-questions@freebsd.org; freebsd-net@freebsd.org >> Subject: Re: OS throws away large packets >> >> Mr Y wrote: >> >>> Hi all, >>> >>> I'm trying to implement Large Recieve Offload for an >>> >> Ethernet driver >> >>> on FreeBSD 6.3, but all my >MTU packets are being thrown by the OS. >>> I'm using mbuf chains in this imlpementation, each mbuf is >>> >> a cluster >> >>> of MCLBYTES bytes. They are linked by the m_next pointer. >>> The first packet being thrown away is 2945 bytes long. >>> >> Wireshark shows >> >>> the packet that is being passed to the OS is correct. >>> >>> Do I need to set some OS parameter to make it recieve mbuf chains? >>> >>> Please help. >>> >>> >> Hi Yony, >> >> I seem to remember some discussion about this list last year >> see the following threads: >> >> >> > http://lists.freebsd.org/pipermail/freebsd-net/2007-September/015250.htm > l > > http://lists.freebsd.org/pipermail/freebsd-net/2007-September/015350.htm > l > > >From my limited reading of these threads just now and possibly bad > memory. It would seem that the MRU to MTU relationship is defined in > the nic driver rather than > >> enforced further up the stack or at least that seamed to be the case >> > with the bce driver. > >> Hope this is helpful, >> >> Tom >> > > Hi Tom, > > >From what I understand these threads are referring to the bce hardware > configuration (bus configuration) and driver mbuf allocation size. Am I > correct? > In my case I'm not trying to receive packets >MTU from the HW, but to > chain mbuf clusters, each is MCLBYTES long, and pass the mbuf chain to > the OS. > Since tcpdump (analyzed by wireshark) catches the packets above the > driver and reports a good packet (and 2945 bytes long), I assume my > driver functionality is ok. From what I know tcpdump is supposed to > immitate the way the stack sees the packet, yet it is discarded. > My logic says there is an OS parameter handled by the driver (at net > device init time for example) that will set the OS to receive large mbuf > chains, or a kernel tcp parameter. Is the tcp stack submitted to the mtu > somehow? > > I don't see where you've identified what version of the os you're working with. There's a check in the 802.3 input path on earlier systems to discard frames >mtu. This was removed not too long ago with LRO in mind; check the history of sys/net/if_ethersubr.c. Sam
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