Network instability with jumbo frames on a G5

[Julio Merino]

Hi all,

I'm trying to enable jumbo frames on my PowerMac G5 but I'm running into
trouble. As soon as I type "ifconfig bge0 mtu 9000", the kernel prints this:

[zone: mbuf_jumbo_9k] kern.ipc.nmbjumbo9 limit reached

and the ifconfig command gets stuck. This obviously shouldn't be happening
on a default configuration (right?).

If I then bump kern.ipc.nmbjumbo9 (to ~40k, which is a bit bigger than the
default ~32k), then the ifconfig command gets unstuck and the network
becomes responsive again... to some extent. But whichever connection
triggers a jumbo frame gets stuck: for example, managing the machine over
SSH is impossible as any command that prints a lot of output quickly will
cause the connection to stall and die.

I've also tried with a smaller jumbo frame (4072) and observed the same
issues.

This is on a machine with 10GB of RAM and this adapter:

bge0: <Broadcom BCM5714 B3, ASIC rev. 0x008003> mem
0xfa530000-0xfa53ffff,0xfa520000-0xfa52ffff irq 66 at device 4.0
numa-domain 0 on pci3
bge0: CHIP ID 0x00008003; ASIC REV 0x08; CHIP REV 0x80; PCI-X 33 MHz

I'm now wondering if this could be related to the problems I was observing
with USB drives as reported here:
https://docs.freebsd.org/cgi/getmsg.cgi?fetch=0+0+archive/2021/freebsd-ppc/20210404.freebsd-ppc.
That said, the machine has been very stable otherwise...

Any ideas?

Thanks

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