RE: [PATCH v3 05/15] xprtrdma: Remove last ib_reg_phys_mr() call site

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> -----Original Message-----
> From: linux-nfs-owner@xxxxxxxxxxxxxxx [mailto:linux-nfs-owner@xxxxxxxxxxxxxxx] On Behalf Of Jason Gunthorpe
> Sent: Tuesday, July 21, 2015 5:55 PM
> To: Steve Wise
> Cc: 'Tom Talpey'; 'Chuck Lever'; linux-rdma@xxxxxxxxxxxxxxx; linux-nfs@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3 05/15] xprtrdma: Remove last ib_reg_phys_mr() call site
> 
> On Tue, Jul 21, 2015 at 05:41:22PM -0500, Steve Wise wrote:
> > On 7/20/2015 5:42 PM, Jason Gunthorpe wrote:
> > >On Mon, Jul 20, 2015 at 05:41:27PM -0500, Steve Wise wrote:
> > >>>B) why bother to check? Are machines with <4GB interesting, and worth
> > >>>supporting a special optimization?
> > >>No, but cxgb3 is still interesting to user applications, and perhaps NFSRDMA using FRMRs.
> > >Doesn't look like the NFS client will work. It requires an all
> > >physical memory lkey for SEND and RECV buffers..
> > >
> > >Jason
> >
> > Looks like cxgb3 supports LOCAL_DMA_LKEY and MEM_MGT_EXTENSIONS so dma mrs
> > aren't required for NFSRDMA:
> >
> > t4:~/linux-2.6/drivers/infiniband/hw/cxgb3 # grep IB_DEVICE_ iwch_provider.c
> >         strlcpy(dev->ibdev.name, "cxgb3_%d", IB_DEVICE_NAME_MAX);
> >         dev->device_cap_flags = IB_DEVICE_LOCAL_DMA_LKEY |
> >                                 IB_DEVICE_MEM_WINDOW |
> >                                 IB_DEVICE_MEM_MGT_EXTENSIONS;
> 
> Neat. Is the dma_mask set properly (I don't see any set at all)?
> 

iw_cxgb3 isn't a PCI driver.  It sits on top of cxgb3 which is the pci device driver and calls pci_set_dma_mask().

> > So cxgb3 can still support NFSRDMA and user verbs w/o get_dma_mr(). I'll
> > submit a patch soon to only support get_dma_mr() if unsigned long is 4
> > bytes...
> 
> So, NFS and RDS seem to be the only iWarp compatible ULPs?
> 
> NFS has worked, and will continue to work with the global lkey.
> 
> RDS looks like it relies on an insecure all physical rkey, so it won't
> work until that is fixed.
> 
> So, I'd just use sizeof(physaddr_t) > 4 as the test. The only people
> that could be impacted are RDS users using distro kernels on machines
> with less than 4G of ram. I somehow doubt there are any of those...
> 
> Jason
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