[openib-general] Re: problem with SDP/AIO on mem-free HCA

[Libor Michalek]

On Fri, Apr 01, 2005 at 08:27:19AM -0800, Roland Dreier wrote:
>     Fab> If you are blessed with a Tavor PRM, see section 8.2.1.6 (in
>     Fab> PRM 1.0.0).  It states that a length of zero in a data
>     Fab> segment indicates a 2GB transfer (MSb is used as a flag to
>     Fab> indicate normal vs. inline data segments).  A zero-byte
>     Fab> request must not reference any data segments.
> 
> Yup, that must be the problem.  I guess mthca can skip over 0-length
> data segments.  Another option would be to say that such work requests
> aren't allowed.  Not sure which way I think we should go.  I need to
> talk to Libor and find out why SDP is generating such requests.

Roland,

  Can you try this patch, it should close a gap to prevent a zero 
length IOCB from getting into the receive data path. 

Thanks.

-Libor

Index: sdp_recv.c
===================================================================
--- sdp_recv.c	(revision 2094)
+++ sdp_recv.c	(working copy)
@@ -297,13 +297,13 @@
 	 * if there is no more advertised space,  queue the
 	 * advertisment for completion
 	 */
-	if (advt->size <= 0)
+	if (!advt->size)
 		sdp_advt_q_put(&conn->src_actv,
 			       sdp_advt_q_get(&conn->src_pend));
 	/*
 	 * if there is no more iocb space queue the it for completion
 	 */
-	if (iocb->len <= 0) {
+	if (!iocb->len) {
 		iocb = sdp_iocb_q_get_head(&conn->r_pend);
 		if (!iocb) {
 			sdp_dbg_warn(conn, "read IOCB disappeared. <%d>",
@@ -1368,26 +1371,11 @@
 		 * RDMA advertisements are checked to determine if remote
 		 * data is pending and accessible.
 		 */
-		if (!(copied < low_water) &&
-		    !conn->src_recv) {
-#if 0 /* performance cheat. LM */
-			if (!(conn->snk_zthresh > size)) {
+		if (copied == size)
+			break;
 
-				conn->nond_recv--;
-
-				result = sdp_send_ctrl_snk_avail(conn,
-								 0, 0, 0);
-				if (result < 0) {
-					/*
-					 * since the message did not go out,
-					 * back out the non_discard counter
-					 */
-					conn->nond_recv++;
-				}
-			}
-#endif
+		if (!(copied < low_water) && !conn->src_recv)
 			break;
-		}
 		/*
 		 * check connection errors, and then wait for more data.
 		 * check status. POSIX 1003.1g order.