Re: Re: Re: [[PATCH v2 for-next]] RDMA/siw: Fix SQ/RQ drain logic

[Leon Romanovsky <leon@kernel.org>]

On Fri, Oct 18, 2019 at 01:50:22PM +0000, Bernard Metzler wrote:
> -----"Leon Romanovsky" <leon@kernel.org> wrote: -----
>
> >To: "Bernard Metzler" <BMT@zurich.ibm.com>
> >From: "Leon Romanovsky" <leon@kernel.org>
> >Date: 10/05/2019 10:26AM
> >Cc: linux-rdma@vger.kernel.org, bharat@chelsio.com, jgg@ziepe.ca,
> >nirranjan@chelsio.com, krishna2@chelsio.com, bvanassche@acm.org
> >Subject: [EXTERNAL] Re: Re: [[PATCH v2 for-next]] RDMA/siw: Fix SQ/RQ
> >drain logic
> >
> >On Fri, Oct 04, 2019 at 02:09:57PM +0000, Bernard Metzler wrote:
> >> -----"Leon Romanovsky" <leon@kernel.org> wrote: -----
> >> <...>
> >>
> >> >>   *
> >> >> @@ -705,6 +746,12 @@ int siw_post_send(struct ib_qp *base_qp,
> >const
> >> >struct ib_send_wr *wr,
> >> >>  	unsigned long flags;
> >> >>  	int rv = 0;
> >> >>
> >> >> +	if (wr && !qp->kernel_verbs) {
> >> >
> >> >It is not related to this specific patch, but all siw
> >"kernel_verbs"
> >> >should go, we have standard way to distinguish between kernel and
> >> >user
> >> >verbs.
> >> >
> >> >Thanks
> >> >
> >> Understood. I think we touched on that already.
> >> rdma core objects have a uobject pointer which
> >> is valid only if it belongs to a user land
> >> application. We might better use that. Let me
> >> see if I can compact QP objects to contain the
> >> ib_qp. I'd like to avoid following pointers
> >> potentially causing cache misses on the
> >> fast path. This is why I still have that
> >> little boolean within the siw private
> >> structure.
> >
> >You have this variable in CQ and SRQ too.
> >
> >I have serious doubts that this value gives any performance
> >advantages.
> >In both flows, you will need to fetch ib_qp pointer, so you don't
> >save
> >here anything by looking on kernel_verbs value.
> >
>
> Yes, I see you are right for both CQ and SRQ.
>
> For the CQ, we have a nested structure where
> siw_cq contains ib_cq. So it is not far away.
>
> For SRQ it is the same.
>
> For QP's we have a split between siw_qp and ib_qp.
> I will look into how to get that one solved.
>
> I will prepare an extra patch for that whole
> kernel_verbs thing, but let's not have it gating
> acceptance of this unrelated patch.

Sure, it is unrelated.

>
> Thanks very much,
> Bernard.
>