[ofa-general] Re: device attributes

[Roland Dreier]

 > Should the device attributes (for instance max_send_wr) be the max
 > supported by the HW or the max supported by the OS or something else?

I think they should be what the consumer can expect to work -- ie the
upper limits on the current system, whether those limits are imposed by
the HW, driver, or whatever.

 > For instance:  Chelsio's HW can handle very large work queues, but
 > since Linux limits the size of contiguous dma coherent memory
 > allocations, the actual limits are much smaller.  Which should I be
 > using for the device attributes?

The smaller limit I think.

 > Also, the chelsio device uses a single work queue to implement the SQ
 > and RQ abstractions.  So the max SQ depth depends on the RQ depth and
 > vice versa.  This leads to device max attributes that aren't that
 > useful.

Not nice... I guess you could return half of the work queue depth for
each max since that is guaranteed to work?

 > I'm wondering what application writes should glean from these attributes...

I think the limits are pointless unless they give something that an
application can actually request.  Some of the limits are pretty
useless, eg max # of CQs, since another app may have already used up all
the CQs.

 - R.