[openib-general] Re: [PATCH 1 of 3] core: static rate encoding changesupport

[Michael S. Tsirkin]

Quoting r. Roland Dreier <rdreier at cisco.com>:
> Subject: Re: [openib-general] Re: [PATCH 1 of 3] core: static rate encoding changesupport
> 
>     Waleri> Michael, Roland, There can be a situation where the
>     Waleri> link/port speed gets changed for example from 12x to 4x...
>     Waleri> Does OpenIb/IPoIB take care about this new configuration,
>     Waleri> i.e. does stack reconfigure all qps by sending modify_qp
>     Waleri> with the new link speed to inform hca about the change or
>     Waleri> should hca take care about reconfiguring the qps?
> 
> No, this is a problem.  IPoIB should be OK because you can't change
> port speeds without bringing the port down first, and that will
> trigger a flush of all IPoIB path information.  But an RC QP can stay
> connected even if the port goes down temporarily, and it would
> continue to use the old static rate information.
> 
> But I don't think this is very likely in practice.

There's no reason to special-case the local port rate change.

Think about remote port rate change, or a link along the path changing, and you
will understand that you can't solve the problem at the verbs layer whatever you
do - its up ULPs to communicate with the SA and figure out that its a good idea
to change the port link rate.

-- 
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies