Re: [PATCH] mlx4: allow for 4K mtu configuration of IB ports

["Jim Schutt" <jaschut-4OHPYypu0djtX7QSmKvirg@public.gmane.org>]

Hi Or,

Or Gerlitz wrote:
> Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> Jim Schutt <jaschut-4OHPYypu0djtX7QSmKvirg@public.gmane.org> wrote:
>>> no good reason to insist that the VL usage is the same for both
>>> interswitch links, and switch-CA links. Do I need to change this?
> 
>> I don't think changing this is a high priority, since it's a pretty small
>> slice of the world, and QoS on the edge links probably is important
>> to an even smaller slice, but IMHO it would be better to give QoS to
>> HCAs that only support 4 VLs by using a different SL2VL table for links to CAs.
> 
> Jim,
> 
> AFAIK, the way opensm applies an SL-to-VL mapping specification (e.g
> dictated by the admin or maybe your routing engine) on a specific link
> is by modulation on the number of active VLs for that link - e.g say
> the ID mapping was required and there are two VLs for that link, so
> we'll have SL-to-VL of 0->0 1->1 2->0 3->1 and so on. So in that
> respect, I wasn't sure what's the change here for you.

Hmmm, can you tell me where such remapping happens?

What I know about so far is the code in sl2vl_update_table(),
which AFAICS truncates VL values in the SL2VL maps provided
by the routing engine to fit into the number of VLs supported
by a port.

Am I missing something else?

torus-2QoS will currently only use VL values 0 and 4 in the
SL2VL maps it generates for CA ports; i.e. any SL maps either
to VL 0 or VL 4, depending on QoS level.

So sl2vl_update_table() would truncate all those VL 4 values
to 0 in the case of ports that support fewer than 8 data VLs.

What I'm suggesting is that I need to make torus-2QoS generate
SL2VL maps that only reference VLs 0 or 1 for CA ports, in order
to allow it to support 2 QoS levels for CA ports that don't
support 8 data VLs.

-- Jim

> 
> Or.
> 
> 


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