Re: FW: [PATCH for 2.6.25] SVCRDMA: Use only 1 RDMA read scatter entry for iWARP adapters

["J. Bruce Fields" <bfields@fieldses.org>]

On Sun, Mar 23, 2008 at 10:06:08PM -0500, Tom Tucker wrote:
> Bruce:
> 
> If possible, this should go in 2.6.25. This was a merge error on my part.
> Thanks to Roland for figuring this out...

Will do, thanks, but, as a subsequent patch, could we clean this up a
little?  For example, assuming sge_count and sc_max_sge are always
positive, isn't the (sge_count > 1) check superfluous, given that the
following min_t's going to produce 1 in that case anyway?

Also, would it be possible just to ensure sc_max_sge is just set to 1
from the start in this case?

--b.

> 
> Tom
> 
> ------ Forwarded Message
> From: Tom Tucker <tom@opengridcomputing.com>
> Date:  Sun, 23 Mar 2008 18:52:49 -0500
> To: Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>, "J. Bruce Fields"
> <bfields@fieldses.org>
> Cc: NeilBrown <neilb@suse.de>, Trond Myklebust <Trond.Myklebust@netapp.com>,
> <linux-nfs@vger.kernel.org>, <linux-kernel@vger.kernel.org>
> Conversation: [PATCH for 2.6.25] SVCRDMA: Use only 1 RDMA read scatter entry
> for iWARP adapters
> Subject: Re: [PATCH for 2.6.25] SVCRDMA: Use only 1 RDMA read scatter entry
> for iWARP adapters
> 
> 
> Ack. It's actually an _ancient_ remnant when it had to compile against iWARP
> vs. non-iWARP enabled OFA trees.
> 
> 
> On 3/23/08 4:27 PM, "Roland Dreier" <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> wrote:
> 
> > The iWARP protocol limits RDMA read requests to a single scatter
> > entry.  NFS/RDMA has code in rdma_read_max_sge() that is supposed to
> > limit the sge_count for RDMA read requests to 1, but the code to do
> > that is inside an #ifdef RDMA_TRANSPORT_IWARP block.  In the mainline
> > kernel at least, RDMA_TRANSPORT_IWARP is an enum and not a
> > preprocessor #define, so the #ifdef'ed code is never compiled.
> > 
> > In my test of a kernel build with -j8 on an NFS/RDMA mount, this
> > problem eventually leads to trouble starting with:
> > 
> >     svcrdma: Error posting send = -22
> >     svcrdma : RDMA_READ error = -22
> > 
> > and things go downhill from there.
> > 
> > The trivial fix is to delete the #ifdef guard.  The check seems to be
> > a remnant of when the NFS/RDMA code was not merged and needed to
> > compile against multiple kernel versions, although I don't think it
> > ever worked as intended.  In any case now that the code is upstream
> > there's no need to test whether the RDMA_TRANSPORT_IWARP constant is
> > defined or not.
> > 
> > Without this patch, my kernel build on an NFS/RDMA mount using NetEffect
> > adapters quickly and 100% reproducibly failed with an error like:
> > 
> >     ld: final link failed: Software caused connection abort
> > 
> > With the patch applied I was able to complete a kernel build on the
> > same setup.
> > 
> > Signed-off-by: Roland Dreier <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>
> > ---
> > I guess this should probably go into 2.6.25 if possible, since things
> > get seriously screwed up in my testing once this bug is hit.
> > 
> > Not sure why this doesn't trigger on Chelsio or Ammasso adapters (or
> > does it?), but it's easily reproducible here on Neteffect adapters
> > (and that driver is now upstream for 2.6.25).
> > 
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > index ab54a73..9712716 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > @@ -237,14 +237,12 @@ static void rdma_set_ctxt_sge(struct svc_rdma_op_ctxt
> > *ctxt,
> >  
> >  static int rdma_read_max_sge(struct svcxprt_rdma *xprt, int sge_count)
> >  {
> > -#ifdef RDMA_TRANSPORT_IWARP
> > if ((RDMA_TRANSPORT_IWARP ==
> >     rdma_node_get_transport(xprt->sc_cm_id->
> >     device->node_type))
> >    && sge_count > 1)
> > return 1;
> > else
> > -#endif
> > return min_t(int, sge_count, xprt->sc_max_sge);
> >  }
> >  
> > --
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