Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags

Sagi Grimberg
2015-07-14T13:23:29Z

On 7/14/2015 3:12 PM, Tom Talpey wrote:
> On 7/14/2015 5:22 AM, Sagi Grimberg wrote:
>> On 7/14/2015 10:37 AM, 'Christoph Hellwig' wrote:
>>> On Mon, Jul 13, 2015 at 03:36:44PM -0400, Tom Talpey wrote:
>>>> On 7/11/2015 6:25 AM, 'Christoph Hellwig' wrote:
>>>>> I think what we need to support for now is FRMR as the primary target,
>>>>> and FMR as a secondar[y].
>>>>
>>>> FMR is a *very* bad choice, for several reasons.
>>>>
>>>> 1) It's not supported by very many devices, in fact it might even
>>>> be thought to be obsolete.
>>>
>>> It's support by the Mellanox adapters,
>>
>> *Older* Mellanox adapters. mlx5 (and future drivers I assume) will
>> no longer support FMRs.
>
> Right, but drop the word "will". Mlx5 (the current ConnectX-4) doesn't
> support FMR. It's only supported by mlx4 and mthca drivers.
>
>>> Based on looking at the consumers and the above table I think FMR
>>> are still the better fallback for devices that don't support FR,
>>
>> It's better if you want it fast.
>
> Do you guys think FMR is actually "fast"? Because it's not. Measure it.
> It might have been marginally faster than other schemes in like, 2007,
> and only when the mempool was there to leave the registrations open.
> Don't go back there.

I agree, I meant the pool API which has obvious problems...

Sagi.