[ofa-general] Re: [PATCH RFC] rds: add iwarp support

[Olaf Kirch]

On Tuesday 08 July 2008 12:29:38 Or Gerlitz wrote:
> Olaf Kirch wrote:
> > As Or already noted, it would be preferable to have IB and iWARP share as much as possible.
> > I understand there probably needs to be a different transport class for iWARP, but I would
> > like iWARP to be some kind of "we do everything like IB except these two little bits" transport.  
>
> Just to clarify, the new "fastreg as work requests" API is NOT iWARP 
> specific, but rather comply in 95% to both IB and iWARP specs. 

Yes, that much I understand. For that reason, the rds_ib_device
has two new flags: is_iwarp (local end point is iwarp device), and
use_fastreg (device supports the fastreg interface, so create a mr_pool
that uses fastreg instead of fmrs)

> Currently, support for these verbs has been posted only for the Chelsio 
> driver (to be merged in 2.6.27-rc1), but Mellanox has made a comment 
> over the list that support for the mlx4 is planned.
> 
> So the distinction is between devices that
> 
> 1. don't support any sort of fastreg
> 2. support the proprietary fmr verbs
> 3. support the standard fastreg as work request verbs
> 
> my understanding is that RDS does not support type one ones, and its a 
> question whether maintainance wise, you want to support type two ones.

Indeed, choice #1 isn't supported. The patch I posted will pick fastreg whenever
the device advertises it. I would have preferred to do it the other way round,
because the fmr code is pretty well tested by now. Unfortunately, there
doesn't seem to be a capability bit that says "I support the fmr interface",
and I didn't really want to start peeking at the function pointers.

> Other then that fastreg issue, and assuming the credit management issue 
> is solved (is it?) is there any difference between IB to iWARP which you 
> see as relevant to RDS v3 (p2p + rdma)?

Yes. credit management is there in 1.4, and on by default.

I have to say I have no clue what other differences between ib and iwarp
may be relevant. I can't think of any, but that's probably just my
lack of imagination.

> The 5% difference are things supported by iWARP but not by IB such as 
> read-with-invalidate, etc

Yeah. Let's get it working first, then

> 
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Olaf Kirch  |  --- o --- Nous sommes du soleil we love when we play
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