Re: [PATCH for-next 06/10] rdma: Set physical MTU for query_port function

[Leon Romanovsky <leon@kernel.org>]

On Tue, Apr 20, 2021 at 08:17:00AM -0400, Dennis Dalessandro wrote:
> On 4/20/2021 1:11 AM, Leon Romanovsky wrote:
> > On Mon, Apr 19, 2021 at 09:08:55AM -0400, Dennis Dalessandro wrote:
> > > On 4/19/2021 8:29 AM, Leon Romanovsky wrote:
> > > > On Mon, Apr 19, 2021 at 12:20:33PM +0000, Wan, Kaike wrote:
> > > > > 
> > > > > 
> > > > > > -----Original Message-----
> > > > > > From: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
> > > > > > Sent: Thursday, April 08, 2021 8:31 AM
> > > > > > To: Leon Romanovsky <leon@kernel.org>
> > > > > > Cc: dledford@redhat.com; jgg@ziepe.ca; linux-rdma@vger.kernel.org; Wan,
> > > > > > Kaike <kaike.wan@intel.com>
> > > > > > Subject: Re: [PATCH for-next 06/10] rdma: Set physical MTU for query_port
> > > > > > function
> > > > > > 
> > > > > > On 4/8/2021 8:14 AM, Leon Romanovsky wrote:
> > > > > > > On Thu, Apr 08, 2021 at 08:06:46AM -0400, Dennis Dalessandro wrote:
> > > > > > > > On 4/1/2021 4:42 AM, Leon Romanovsky wrote:
> > > > > > > > > On Mon, Mar 29, 2021 at 09:54:12AM -0400,
> > > > > > dennis.dalessandro@cornelisnetworks.com wrote:
> > > > > > > > > > From: Kaike Wan <kaike.wan@intel.com>
> > > > > > > > > > 
> > > > > > > > > > This is a follow on patch to add a phys_mtu field to the
> > > > > > > > > > ib_port_attr structure to indicate the maximum physical MTU the
> > > > > > > > > > underlying device supports.
> > > > > > > > > > 
> > > > > > > > > > Extends the following:
> > > > > > > > > > commit 6d72344cf6c4 ("IB/ipoib: Increase ipoib Datagram mode MTU's
> > > > > > > > > > upper limit")
> > > > > > > > > > 
> > > > > > > > > > Reviewed-by: Mike Marciniszyn
> > > > > > > > > > <mike.marciniszyn@cornelisnetworks.com>
> > > > > > > > > > Signed-off-by: Kaike Wan <kaike.wan@intel.com>
> > > > > > > > > > Signed-off-by: Dennis Dalessandro
> > > > > > > > > > <dennis.dalessandro@cornelisnetworks.com>
> > > > > > > > > > ---
> > > > > > > > > >      drivers/infiniband/hw/bnxt_re/ib_verbs.c        |  1 +
> > > > > > > > > >      drivers/infiniband/hw/cxgb4/provider.c          |  1 +
> > > > > > > > > >      drivers/infiniband/hw/efa/efa_verbs.c           |  1 +
> > > > > > > > > >      drivers/infiniband/hw/hns/hns_roce_main.c       |  1 +
> > > > > > > > > >      drivers/infiniband/hw/i40iw/i40iw_verbs.c       |  1 +
> > > > > > > > > >      drivers/infiniband/hw/mlx4/main.c               |  1 +
> > > > > > > > > >      drivers/infiniband/hw/mlx5/mad.c                |  1 +
> > > > > > > > > >      drivers/infiniband/hw/mlx5/main.c               |  2 ++
> > > > > > > > > >      drivers/infiniband/hw/mthca/mthca_provider.c    |  1 +
> > > > > > > > > >      drivers/infiniband/hw/ocrdma/ocrdma_verbs.c     |  1 +
> > > > > > > > > >      drivers/infiniband/hw/qib/qib_verbs.c           |  1 +
> > > > > > > > > >      drivers/infiniband/hw/usnic/usnic_ib_verbs.c    |  1 +
> > > > > > > > > >      drivers/infiniband/hw/vmw_pvrdma/pvrdma_verbs.c |  1 +
> > > > > > > > > >      drivers/infiniband/sw/siw/siw_verbs.c           |  1 +
> > > > > > > > > >      drivers/infiniband/ulp/ipoib/ipoib_main.c       |  2 +-
> > > > > > > > > >      include/rdma/ib_verbs.h                         | 17 -----------------
> > > > > > > > > >      16 files changed, 16 insertions(+), 18 deletions(-)
> > > > > > > > > 
> > > > > > > > > But why? What will it give us that almost all drivers have same
> > > > > > > > > props->phys_mtu = ib_mtu_enum_to_int(props->max_mtu); line?
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > Almost is not all. Alternative idea to convey this? Seemed like a
> > > > > > > > sensible thing to at least have support for but open to other approaches.
> > > > > > > 
> > > > > > > What about leave it as is?
> > > > > > > 
> > > > > > > I'm struggling to get the rationale behind this patch., the code
> > > > > > > already works and set the phys_mtu correctly, isn't it?
> > > > > > 
> > > > > > I see what you are saying now. Kaike, correct me if I'm wrong, but the intent
> > > > > > of this patch is just to make everything behave the same in the sense that a
> > > > > > device could have a different physical MTU. The field got added to the
> > > > > > ib_port_attr previously so this is giving it an initial value vs leaving it unset.
> > > > > [Wan, Kaike]  Correct.
> > > > 
> > > > No one is using this "phys_mtu" field, except one place in ipoib.
> > > 
> > > Today. I think it would be better to formalize the idea though and have a
> > > cleaner interface. Does this cause some problem?
> > 
> > Not directly, but yes.
> > 
> > Before your change, drivers don't need to care about this field because
> > it is not in use at all, after your change all drivers need to carry same
> > line. This is prone to errors.
> 
> Perhaps a more common place to set this in the core is appropriate.

This is basically what I suggested to Kaike.

Thanks

> 
> -Denny
> 
>