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Date:   Tue, 6 Apr 2021 14:30:34 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Jason Gunthorpe <jgg@nvidia.com>
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Subject: Re: [PATCH rdma-next 01/10] RDMA: Add access flags to
 ib_alloc_mr() and ib_mr_pool_init()
Message-ID: <20210406123034.GA28930@lst.de>
References: <20210405052404.213889-1-leon@kernel.org> <20210405052404.213889-2-leon@kernel.org> <c21edd64-396c-4c7c-86f8-79045321a528@acm.org> <YGvwUI022t/rJy5U@unreal> <20210406052717.GA4835@lst.de> <YGv4niuc31WnqpEJ@unreal> <20210406121312.GK7405@nvidia.com>
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On Tue, Apr 06, 2021 at 09:13:12AM -0300, Jason Gunthorpe wrote:
> So we broadly have two choice
>  1) Diverge the kernel and user interfaces and make the RDMA drivers
>     special case all the kernel stuff to force
>     ACCESS_RELAXED_ORDERING when they are building MRs and processing
>     FMR WQE's
>  2) Keep the two interfaces the same and push the
>     ACCESS_RELAXED_ORDERING to a couple of places in the ULPs so the
>     drivers see a consistent API
> 
> They are both poor choices, but I think #2 has a greater chance of
> everyone doing their parts correctly.

No, 1 is the only sensible choice.  The userspace verbs interface is
a mess and should not inflict pain on the kernel in any way.  We've moved
away from a lot of the idiotic "Verbs API" concepts with things like
how we handle the global lkey, the new CQ API and the RDMA R/W
abstraction and that massively helped the kernel ecosystem.