RE: [EXTERNAL] Re: [PATCH rdma-next 1/1] RDMA/mana_ib: indicate that inline data is not supported

Konstantin Taranov
2024-07-18T15:06:02Z

> > > > Yes, you are. If user asked for specific functionality
> > > > (max_inline_data != 0) and your device doesn't support it, you should
> return an error.
> > > >
> > > > pvrdma, mlx4 and rvt are not good examples, they should return an
> > > > error as well, but because of being legacy code, we won't change them.
> > > >
> > > > Thanks
> > > >
> > >
> > > I see. So I guess we can return a larger value, but not smaller. Right?
> > > I will send v2 that fails QP creation then.
> > >
> > > In this case, may I submit a patch to rdma-core that queries device
> > > caps before trying to create a qp in rdma_client.c and
> > > rdma_server.c? As that code violates what you described.
> >
> > Let's ask Jason, why is that? Do we allow to ignore max_inline_data?
> >
> > librdmacm/examples/rdma_client.c
> > 63 memset(&attr, 0, sizeof attr);
> > 64 attr.cap.max_send_wr = attr.cap.max_recv_wr = 1;
> > 65 attr.cap.max_send_sge = attr.cap.max_recv_sge = 1;
> > 66 attr.cap.max_inline_data = 16;
> > 67 attr.qp_context = id;
> > 68 attr.sq_sig_all = 1;
> > 69 ret = rdma_create_ep(&id, res, NULL, &attr);
> > 70 // Check to see if we got inline data allowed or not
> > 71 if (attr.cap.max_inline_data >= 16)
> > 72 send_flags = IBV_SEND_INLINE;
> > 73 else
> > 74 printf("rdma_client: device doesn't support
> IBV_SEND_INLINE, "
> > 75 "using sge sends\n");
>
> I think the idea expressed in this code is that if max_inline_data requested
> too much it would be limited to the device capability.
>
> ie qp creation should limit the requests values to what the HW can do, similar
> to how entries and other work.
>
> If the HW has no support it should return - for max_inline_data not an error,
> I guess?

Yes, this code implies that max_inline_data can be ignored at creation, while the manual of ibv_create_qp says:
"The function ibv_create_qp() will update the qp_init_attr->cap struct with the actual QP values of the QP that was created;
the values will be **greater than or equal to** the values requested."

I see two options:
1) Remove code from rdma examples that rely on ignoring max_inline; add a warning to libibverbs when drivers ignore that value.
2) Add to manual that max_inline_data might be ignored by drivers; and allow my current patch that ignores max_inline_data in mana_ib.

I am fine to implement either of two. Please, reply which one you think more correct. I guess option 2 is the safest, but option 1
is more correct in my opinion.

Thanks

>
> Jason