[Openib-windows] Adding an environment variable for determining the initial CQ size

[Fabian Tillier]

Hi Tzachi,

On 7/12/06, Tzachi Dar <tzachid at mellanox.co.il> wrote:
>
> Hi Fab,
>
> The following patch does two things:
> 1) It adds a new environment variable (IBWSD_INITIAL_CQ_SIZE) that controls
> the number of QPs that will use the same CQ.

Is this worth doing?  Isn't the MTHCA driver going to have CQ resize
support soon?  I was under the impression that the existing code to
size the CQ to support 100 QPs was temporary until MTHCA was updated.
This change makes me think that resize CQ support is not going to
happen anytime soon.

> 2) It sets the default value from 100 to 500. We believe that this will
> allow the users to work on bigger Clusters while the increase in memory is
> negligible for a modern system.

Can you quantify the memory footprint of a CQ sized for 500 QPs, each
of which has 32 entries (so 16000 entries)?  What's the size of each
CQE?

Also, what is preventing the existing implementation from workign on
large clusters?  I don't understand what the problem we're trying to
solve is.

As to the patch itself, it would be better to rename initial_cq_size
to initial_qp_per_cq or something like that, since that's what's being
controlled here.  This applies to both the environment variable and
the internal global variable.

Thanks,

- Fab