Unlike other controllers which have more advanced jumbo support,
these controllers have one send ring, one standard receive producer
ring and one receive return ring. In order to receive jumbo frames
on the controllers, driver now will increase Rx buffer size to 9k.
Two Rx modes are supported on these controllers and I chose
standard Rx BDs over extended Rx BDs. The extended Rx BD mode
allows up to 4 segmentations for each Rx BDs such that kernel does
not have to allocate large buffer of contiguous memory for
receiving. The extended Rx BD mode is already used on controllers
that have separate jumbo receive ring. However, using extended Rx
BDs on BCM5714/BCM5715/BCM5780 reduces the number of Rx BDs to 256
entries which in turn may reduce the performance. Also UMA backed
page allocator for jumbo frame returns contiguous memory so using
extended Rx BD has no advantage on FreeBSD unless highly customized
local allocator implemented in driver is used.
To use jumbo buffers in standard receive ring, Rx buffer allocation
handler was changed to allocate MJUM9BYTES sized mbuf.
PR: kern/155192
Tested by: Vijay Singh <vijju.singh <> gmail dot com>
Submitted by: mjacob (initial version)
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