> -----Original Message----- > From: linux-rdma-ow...@vger.kernel.org > [mailto:linux-rdma-ow...@vger.kernel.org] On Behalf Of Steve Wise > Sent: Friday, July 24, 2015 2:58 PM > To: 'Jason Gunthorpe' > Cc: dledf...@redhat.com; infinip...@intel.com; sa...@mellanox.com; > ogerl...@mellanox.com; r...@mellanox.com; linux- > r...@vger.kernel.org; e...@mellanox.com; target-de...@vger.kernel.org; > linux-...@vger.kernel.org; bfie...@fieldses.org > Subject: RE: [PATCH V6 9/9] isert: Support iWARP transports using FRMRs > > > > > -----Original Message----- > > From: Jason Gunthorpe [mailto:jguntho...@obsidianresearch.com] > > Sent: Friday, July 24, 2015 2:24 PM > > To: Steve Wise > > Cc: dledf...@redhat.com; infinip...@intel.com; sa...@mellanox.com; > > ogerl...@mellanox.com; r...@mellanox.com; linux- > > r...@vger.kernel.org; e...@mellanox.com; target-de...@vger.kernel.org; > > linux-...@vger.kernel.org; bfie...@fieldses.org > > Subject: Re: [PATCH V6 9/9] isert: Support iWARP transports using FRMRs > > > > On Fri, Jul 24, 2015 at 01:48:09PM -0500, Steve Wise wrote: > > > > The use of FRWR for RDMA READ should be iWarp specific, IB shouldn't > > > > pay that overhead. I am expecting to see a cap_rdma_read_rkey or > > > > something in here ? > > > > > > Ok. But cap_rdma_read_rkey() doesn't really describe the > > > requirement. The requirement is rkey + REMOTE_WRITE. So it is more > > > like rdma_cap_read_requires_remote_write() which is ugly and too > > > long (but descriptive)... > > > > I don't care much what name you pick, just jam something like this in > > the description > > > > If set then RDMA_READ must be performed by mapping the local > > buffers through a rkey MR with ACCESS_REMOTE_WRITE enabled. > > The rkey of this MR should be passed in as the sg_lists's lkey for > > IB_WR_RDMA_READ_WITH_INV. > > > > FRWR should be used to register the buffer in the send queue, > > and the read should be issued using IB_WR_RDMA_READ_WITH_INV (xx > > can we just implicitly rely on this? Are there any iWarp cards that > > support FRWR but not WITH_INV?) > > > > No. And iWARP devices must support READ_WITH_INV from my reading of the > iWARP verbs spec. > > I will add all these comments and make use of READ_WITH_INV. > > > Finally, only a single SGE can be used with RDMA_READ, all scattering > > must be accomplished with the MR. > > > > This quite dramatically changes what is an allowed scatter for the > > transfer, IB can support arbitary unaligned S/G lists, while this is > > now forced into gapless page aligned elements. > > > > Your patch takes care of this? And only impacts IB? > > Did you mean "only impacts iWARP?" > > Yes the patch takes care of sg->fr page list packing. And it uses the > existing isert_map_fr_pagelist() to pack the sg into the > fastreg page list. This same routine is used by the IB FRMR/PI reg/unreg > routines as well. >
By the way, just to be clear: If you use a FRWR, you by definition only have one SGE entry as the result of the registration. So regardless of what a device/protocol can do with the destination SGE of an RDMA READ operation, if you use FRWR to register the destination region, you need only 1 SGE in the RDMA READ WR. Stevo. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
