RE: Kernel fast memory registration API proposal [RFC]

["Steve Wise" <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

> -----Original Message-----
> From: Jason Gunthorpe [mailto:jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org]
> Sent: Wednesday, July 15, 2015 2:10 PM
> To: Steve Wise
> Cc: 'Sagi Grimberg'; 'Christoph Hellwig'; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; 'Or Gerlitz'; 'Oren Duer'; 'Chuck Lever'; 'Bart Van Assche';
'Liran
> Liss'; 'Hefty, Sean'; 'Doug Ledford'; 'Tom Talpey'
> Subject: Re: Kernel fast memory registration API proposal [RFC]
> 
> > >   - ULP calls a 'rdma_post_close_rkey' helper
> > >      * For FRWR this posts the INVALIDATE
> >
> > Note: Some send operations automatically invalidate an rkey (and the
> > lkey for IB?).  This is intended to avoid having to post the
> > invalidate WR explicitly.  Namely IB_WR_READ_WITH_INV and
> > IB_WR_SEND_WITH_INV.
> 
> IB_WR_RDMA_READ_WITH_INV is only meaningful/implemented for iWarp. Can
> you confirm what it does?
> 
>  wc.opcode = IB_WR_RDMA_READ_WITH_INV
>  wc.sg_list[0].lkey = LKEY;
>  wc.rdma.rkey = RKEY;
> 
> Does it locally invalidate LKEY or remotely invalidate RKEY? I'm
> feeling pretty confident to guess it invalidates LKEY..

Yes, it invalidates the MR associated with LKEY.

> 
> 'rdma_post_close_rkey' wouldn't work with lkeys, hence the name :)
> 
> IB_WR_SEND_WITH_INV is sadly never used in the kernel. It does
> invalidate an rkey, and would have to interact with a
> 'rdma_post_close_rkey'.
> 
> A generic flow could be something like:
> 
>   if (rdma_post_close_rkey_wc(qp,rkey,wc,...) ..)
>     // invalidate triggred by the peer, all done.
>   else
>     // Peer didn't invalidate, func queued it locally, ULP waits for the next completion, then all done.
>   else
>     // Error
> 
> Where the _wc varient checks the wc to confirm that the requested rkey
> has been invalidated.
> 
> Jason

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