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From: "'Christoph Hellwig'" <hch@infradead.org>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
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Subject: Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags
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On Thu, Jul 09, 2015 at 11:01:42AM -0600, Jason Gunthorpe wrote:
> To your point in another message, I'd say, as long as the new API
> supports FRMR at full speed with no performance penalty we are
> good. If the other variants out there take a performance hit, then I
> think that is OK. As you say, they are on the way out, we just need to
> make sure that ULPs continue to work with FMR with the new API so
> legacy cards don't completely break.

I think what we need to support for now is FRMR as the primary target,
and FMR as a secondard.  A few in-kernel drivers support physical
registrations, but it's always been clear that they've been a bad idea,
and the current discussion reconfirms that again.

So a FRMR-like API that allows to use FMRs underneath might be a good
start.  If the imput to that API are S/G lists as in my suggestion we'll
get indirect registration support almost for free.