Changing MTU on cxgbe

[Navdeep Parhar]

On Fri, May 27, 2016 at 12:23:02AM -0700, K. Macy wrote:
> On Thursday, May 26, 2016, Navdeep Parhar <nparhar at gmail.com> wrote:
> 
> > On Fri, May 27, 2016 at 12:57:34AM -0400, Garrett Wollman wrote:
> > > In article <
> > CAJpsHY4vF5Ky6GuAusLOOROgiQuyD2CcRmVxu8x3cArQRZxcbg at mail.gmail.com
> > <javascript:;>> you write:
> > >
> > > ># ifconfig -m cxgbe0
> > > >cxgbe0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST>
> > >
> > > ># ifconfig cxgbe0 mtu 9000
> > > >ifconfig: ioctl SIOCSIFMTU (set mtu): Invalid argument
> > >
> > > I believe this device, like many others, does not allow the MTU (or
> > > actually the MRU) to be changed once the receive ring has been set up
> >
> > This is not correct.  You can change the MTU of a cxgbe/cxl interface at
> > any time (whether it's up or down, passing traffic or idle, etc.).
> 
> 
> For some reason the stack needs init to be called when the MTU is changed
> for it to actually change the size of the packets passed to the driver. At
> least cxgb does not do that. I'm not at my computer right now, but cxgbe
> may be the same. If that's the case just up / down the interface. It _will_
> take effect without that if it's passed at module load.

The problem that was reported was that the ioctl that sets the MTU
failed, not that the ioctl succeeded but the MTU change did not take
effect.

Regards,
Navdeep