RE: [PATCH 7/9] IB/core: generic RDMA READ/WRITE API

Steve Wise
2016-03-01T15:47:24Z

> -----Original Message-----
> From: Sagi Grimberg [mailto:sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org]
> Sent: Tuesday, March 01, 2016 3:20 AM
> To: Christoph Hellwig
> Cc: Steve Wise; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org; bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org; target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Subject: Re: [PATCH 7/9] IB/core: generic RDMA READ/WRITE API
>
>
> >>>> + if (rdma_rw_use_mr(qp->device, port_num)) {
> >>>> + ret = rdma_rw_init_mr_wrs(ctx, qp, port_num, sg, sg_offset,
> >>>> + remote_addr, rkey, dir);
> >>>
> >>> At some point I would like the iWARP IO to do no-mr for WRITE/dma_nents
> >>> == 1, and WRITE/dma_nents <= max_send_sge for the device. I think this
> >>> will help smaller iSER/NVMEF READ IOPs. I'm testing this out now on the
> >>> NVMEF code, which is slightly different. If it proves out to better the
> >>> performance, I'll post a follow-on patch...
> >>
> >> Is this possible given that pd->local_dma_lkey has only local
> >> permissions?
> >
> > I think he means NVMe / SCSI READ commands, which use RDMA WRITE.
> > For NVMe / SCSI WRITE commands that use RDMA READ all bets are off
> > for iWarp, but at least it supports READ W/ INVALIDATE.
>
> I interpreted "no-mr for WRITE/dma_nents == 1" as either RDMA_WRITE of
> RDMA_READ with a single dma entry (and that part I didn't understand).

I mean for iWARP, we can do RDMA WRITE operations w/o a MR, if the ib_sge is small enough given the device max send depth.

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