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: Chuck Lever <chuck.lever@oracle.com> Reviewed-by: Sagi Grimberg <sagig@mellanox.com> Tested-by: Devesh Sharma <devesh.sharma@avagotech.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
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@ -420,7 +420,7 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
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*
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* o Read ops return data as write chunk(s), header as inline.
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* o If the expected result is under the inline threshold, all ops
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* return as inline (but see later).
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* return as inline.
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* o Large non-read ops return as a single reply chunk.
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*/
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if (rqst->rq_rcv_buf.flags & XDRBUF_READ)
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@ -476,17 +476,6 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
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headerp->rm_body.rm_nochunks.rm_empty[2] = xdr_zero;
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/* new length after pullup */
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rpclen = rqst->rq_svec[0].iov_len;
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/* Currently we try to not actually use read inline.
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* Reply chunks have the desirable property that
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* they land, packed, directly in the target buffers
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* without headers, so they require no fixup. The
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* additional RDMA Write op sends the same amount
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* of data, streams on-the-wire and adds no overhead
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* on receive. Therefore, we request a reply chunk
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* for non-writes wherever feasible and efficient.
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*/
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if (wtype == rpcrdma_noch)
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wtype = rpcrdma_replych;
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}
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if (rtype != rpcrdma_noch) {
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