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

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Date:	Sun, 23 Mar 2008 18:52:49 -0500
From:	Tom Tucker <tom@...ngridcomputing.com>
To:	Roland Dreier <rdreier@...co.com>,
	"J. Bruce Fields" <bfields@...ldses.org>
CC:	NeilBrown <neilb@...e.de>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	<linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
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@...co.com> 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@...co.com>
> ---
> 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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