[openib-general] Re: RDMA memory registration

[David Addison]

Ronald G. Minnich wrote:
> 
> On Fri, 29 Apr 2005, Greg Lindahl wrote:
> 
>>It doesn't imply that there's an MMU, either. I know that Myricom uses a
>>little lookup routine in software on their nic, which most people
>>wouldn't call an MMU. I don't know what Mellanox does for this, they
>>don't talk much about what's hardware and what's software on their nic.
>>I think Quadrics actually uses the TLB of their risc cpu on their nic
>>for this lookup, but that's just a guess.
> 
> but only quadrics rewrites the mm layer code ..
> 
>
Hi Ron,
as our recent IOPROC patch on lkml shows, it's not that invasive. There
are just 24 hooks added to the Linux VM code paths - which we have been able to
maintain outside the mainline tree for many years now.
As these hooks only need to synchronise the Elan's MMU state with that of the
CPU, the device drivers calls don't change the Linux MM behaviour.

We believe the IOPROC patch is generic and powerful and would allow other
RDMA NICs to solve the page registration problems in a different manner.
For NICs which require page registration, new VM hooks can be used to avoid
pages being unloaded whilst DMAs are active. Our latest cut of the IOPROC patch
has such a hook.


Cheers
Addy.