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svcrdma: Single-stage RDMA Read

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Currently the generic RPC server layer calls svc_rdma_recvfrom()
twice to retrieve an RPC message that uses Read chunks. I'm not
exactly sure why this design was chosen originally.

Instead, let's wait for the Read chunk completion inline in the
first call to svc_rdma_recvfrom().

The goal is to eliminate some page allocator churn.
rdma_read_complete() replaces pages in the second svc_rqst by
calling put_page() repeatedly while the upper layer waits for the
request to be constructed, which adds unnecessary NFS WRITE round-
trip latency.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Tom Talpey <tom@talpey.com>
This commit is contained in:
Chuck Lever
2020-12-22 13:22:20 -05:00
parent 82011c80b3
commit 7d81ee8722
2 changed files with 37 additions and 67 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
View File

@@ -853,6 +853,9 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
spin_unlock(&rdma_xprt->sc_rq_dto_lock);
percpu_counter_inc(&svcrdma_stat_recv);
/* Unblock the transport for the next receive */
svc_xprt_received(xprt);
ib_dma_sync_single_for_cpu(rdma_xprt->sc_pd->device,
ctxt->rc_recv_sge.addr, ctxt->rc_byte_len,
DMA_FROM_DEVICE);
@@ -884,33 +887,28 @@ complete:
rqstp->rq_xprt_ctxt = ctxt;
rqstp->rq_prot = IPPROTO_MAX;
svc_xprt_copy_addrs(rqstp, xprt);
svc_xprt_received(xprt);
return rqstp->rq_arg.len;
out_readlist:
ret = svc_rdma_process_read_list(rdma_xprt, rqstp, ctxt);
if (ret < 0)
goto out_readfail;
svc_xprt_received(xprt);
return 0;
goto complete;
out_err:
svc_rdma_send_error(rdma_xprt, ctxt, ret);
svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
svc_xprt_received(xprt);
return 0;
out_readfail:
if (ret == -EINVAL)
svc_rdma_send_error(rdma_xprt, ctxt, ret);
svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
svc_xprt_received(xprt);
return ret;
out_backchannel:
svc_rdma_handle_bc_reply(rqstp, ctxt);
out_drop:
svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
svc_xprt_received(xprt);
return 0;
}