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xprtrdma: Avoid using Write list for small NFS READ requests

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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 9d11b51ce7 ('svcrdma: Fix send_reply()
scatter/gather set-up'). Commit 9d11b51ce7 was introduced in v4.3,
and is included in 4.2.y, 4.1.y, and 3.18.y.

Oracle bug 22925946 has been filed to request that the above fix
be included in the Oracle Linux UEK4 NFS/RDMA server.

Red Hat bugzillas 1327280 and 1327554 have been filed to request
that RHEL NFS/RDMA server backports include the above fix.

Workaround: Replace the "proto=rdma,port=20049" mount options
with "proto=tcp" until commit 9d11b51ce7 is applied to your
NFS server.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Chuck Lever 2016-05-02 14:41:14 -04:00 committed by Anna Schumaker
parent 302d3deb20
commit cce6deeb56
1 changed files with 5 additions and 4 deletions
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9
net/sunrpc/xprtrdma/rpc_rdma.c
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@ -539,15 +539,16 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
/* /*
* Chunks needed for results? * 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 * o If the expected result is under the inline threshold, all ops
* return as inline. * 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. * o Large non-read ops return as a single reply chunk.
*/ */
if (rqst->rq_rcv_buf.flags & XDRBUF_READ) if (rpcrdma_results_inline(r_xprt, rqst))
wtype = rpcrdma_writech;
else if (rpcrdma_results_inline(r_xprt, rqst))
wtype = rpcrdma_noch; wtype = rpcrdma_noch;
else if (rqst->rq_rcv_buf.flags & XDRBUF_READ)
wtype = rpcrdma_writech;
else else
wtype = rpcrdma_replych; wtype = rpcrdma_replych;