iscsi: nodelay fix

I'm not sure about this. I don't think that NODELAY option hurts performance. However, open-iscsi does not use MSG_MORE properly with sendpage, so NODELAY option hurts the open-iscsi performance.

I've attached a patch to fix NODELAY and MSG_MORE problems and the write performance results with disktest.

I use Opteron boxes connected directly, Chelsio NICs, 1500-byte MTU, 64 KB I/O size, and the iSCSI parameters on open-iscsi web site.

With only NODELAY fix, the performance drops, as you said. On the other hand, NODELAY and MSG_MORE fixes improve the performance overall.

@@ -1385,7 +1385,7 @@ iscsi_sendpage(struct iscsi_conn *conn, 
 	BUG_ON(buf->sent + size > buf->sg.length);
 	if (size > *count)
 		size = *count;
-	if (buf->sent + size != buf->sg.length)
+	if (buf->sent + size != buf->sg.length || *count != size)
 		flags |= MSG_MORE;
 
 	res = iscsi_send(sk, buf, size, flags);