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Commit 33943b29 authored by Chuck Lever's avatar Chuck Lever Committed by Anna Schumaker
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xprtrdma: Don't provide a reply chunk when expecting a short reply 



Currently Linux always offers a reply chunk, even when the reply
can be sent inline (ie. is smaller than 1KB).

On the client, registering a memory region can be expensive. A
server may choose not to use the reply chunk, wasting the cost of
the registration.

This is a change only for RPC replies smaller than 1KB which the
server constructs in the RPC reply send buffer. Because the elements
of the reply must be XDR encoded, a copy-free data transfer has no
benefit in this case.

Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
Reviewed-by: default avatarSagi Grimberg <sagig@mellanox.com>
Tested-by: default avatarDevesh Sharma <devesh.sharma@avagotech.com>
Signed-off-by: default avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
parent 02eb57d8

net/sunrpc/xprtrdma/rpc_rdma.c

+1 −12
Original line number Diff line number Diff line
@@ -420,7 +420,7 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst) 
	 *

	 * 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 (but see later).

	 *   return as inline.

	 * o Large non-read ops return as a single reply chunk.

	 */

	if (rqst->rq_rcv_buf.flags & XDRBUF_READ)
@@ -476,17 +476,6 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst) 
		headerp->rm_body.rm_nochunks.rm_empty[2] = xdr_zero;

		/* new length after pullup */

		rpclen = rqst->rq_svec[0].iov_len;

		/* Currently we try to not actually use read inline.

		 * Reply chunks have the desirable property that

		 * they land, packed, directly in the target buffers

		 * without headers, so they require no fixup. The

		 * additional RDMA Write op sends the same amount

		 * of data, streams on-the-wire and adds no overhead

		 * on receive. Therefore, we request a reply chunk

		 * for non-writes wherever feasible and efficient.

		 */

		if (wtype == rpcrdma_noch)

			wtype = rpcrdma_replych;

	}



	if (rtype != rpcrdma_noch) {