[ofa-general] Re: [PATCH] IB/IPoIB: Fix change mtu when switching to UD mode

[Eli Cohen]

On Mon, Jun 30, 2008 at 08:12:46PM -0700, Roland Dreier wrote:
>  > When changing from CM mode to UD mode, use the kernel function
>  > dev_set_mtu() instead of directly setting dev->mtu. This is necessary
>  > so any other subsystem that need to know about this will (this is done
>  > through the call to call_netdevice_notifiers().
> 
> What type of breakage do we get without this patch?
Nothing that I could see but it seems the right way to do it anyway.
Here's a short history I got to it. I sent you a few weeks ago a patch
that sets the MTU to the max supported by CM mode when moving to CM
mode (through the sysfs mode file, sorry I can't send  url now since
the openfabrics web server is down at the moment), for which you did
not response yet. I took that patch to ofed however.
Then, a week ago, I started getting complains from the mailing list on
drop of performance in CM mode. I noticed it happens when changing
from UD to CM mode but if I changed the MTU from the command line, I
did not experience this problem. Investigating a litte farther, I came
to this solution which fixed the CM problem too.
So I intend to send, later, the original patch again but with this
modification as well.

> Does the assignment
> of dev->mtu in ipoib_mcast_join_task() need the same conversion?
I think it does, though I haven't checked the effect of this yet.