Subject: Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags
To: Tom Talpey <tom@talpey.com>, "'Christoph Hellwig'" <hch@infradead.org>
References: <559BFE03.4020709@dev.mellanox.co.il>
 <20150707213628.GA5661@obsidianresearch.com>
 <559CD174.4040901@dev.mellanox.co.il>
 <20150708190842.GB11740@obsidianresearch.com> <559D983D.6000804@talpey.com>
 <20150708233604.GA20765@obsidianresearch.com>
 <559E54AB.2010905@dev.mellanox.co.il>
 <20150709170142.GA21921@obsidianresearch.com>
 <20150711102538.GB14741@infradead.org> <55A4134C.2040301@talpey.com>
 <20150714073756.GB7630@infradead.org> <55A4D4C6.6040907@dev.mellanox.co.il>
 <55A4FCB2.8090909@talpey.com>
Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        Steve Wise <swise@opengridcomputing.com>, dledford@redhat.com,
        sagig@mellanox.com, ogerlitz@mellanox.com, roid@mellanox.com,
        linux-rdma@vger.kernel.org, eli@mellanox.com,
        target-devel@vger.kernel.org, linux-nfs@vger.kernel.org,
        trond.myklebust@primarydata.com, bfields@fieldses.org,
        Oren Duer <oren@mellanox.com>
From: Sagi Grimberg <sagig@dev.mellanox.co.il>
Message-ID: <55A50D51.7030808@dev.mellanox.co.il>
Date: Tue, 14 Jul 2015 16:23:29 +0300
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Sender: linux-nfs-owner@vger.kernel.org

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.