[PATCH v1 05/18] xprtrdma: Avoid using Write list for small NFS READ requests

Chuck Lever
2016-04-11T20:10:50Z

Avoid the latency and interrupt overhead of registering a Write
chunk when handling NFS READ requests of a few hundred bytes or
less.

This change does not interoperate with Linux NFS/RDMA servers
that do not have commit 9d11b51ce7c1 ('svcrdma: Fix send_reply()
scatter/gather set-up').

$ git describe 9d11b51ce7c1
v4.2-rc3-10-g9d11b51

Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
---
net/sunrpc/xprtrdma/rpc_rdma.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index 205b81b..0105e65 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -539,15 +539,16 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
/*
* Chunks needed for results?
*
- * o Read ops return data as write chunk(s), header as inline.
* o If the expected result is under the inline threshold, all ops
* return as inline.
+ * o Large read ops return data as write chunk(s), header as
+ * inline.
* o Large non-read ops return as a single reply chunk.
*/
- if (rqst->rq_rcv_buf.flags & XDRBUF_READ)
- wtype = rpcrdma_writech;
- else if (rpcrdma_results_inline(r_xprt, rqst))
+ if (rpcrdma_results_inline(r_xprt, rqst))
wtype = rpcrdma_noch;
+ else if (rqst->rq_rcv_buf.flags & XDRBUF_READ)
+ wtype = rpcrdma_writech;
else
wtype = rpcrdma_replych;