What the Secret Sauce for Using Jumbo 9K Mbufs?

[M. Warner Losh]

In message: <22C21BFBEB52B340A1F422CB0D88F5872E0C at snoopy.randomparity.com>
            "David Christensen" <dave at randomparity.com> writes:
: I was hoping to add Jumbo frame support in my Ethernet driver 
: by using m_getjcl() to allocate MJUM9BYTES sized mbufs to my
: receive ring but I'm getting the error EFBIG when I try to map
: the mbuf into device memory with bus_dmamap_load_mbuf().  The
: implementation is very similar to what's done in the myri10ge
: driver so I'm not sure what's needed.  I tried adding 
: kern.ipc.nmbjumbo9=1024 to my /etc/sysctl.conf but that didn't
: make a difference either.  What am I missing?  If I do get it
: working, how far back in time can I back port the driver using
: 9K mbufs?
: 
: I'm developing on FreeBSD 7.0-CURRENT with an amd64 system.

Have you made sure that the dma map specifies a large enough maximum
segment size?

Warner