2015-11-12 14:44:37

by Chuck Lever III

Subject: [PATCH] svcrdma: Do not send XDR roundup bytes for a write chunk

Minor optimization: when dealing with write chunk XDR roundup, do
not post a Write WR for the zero bytes in the pad. Simply update
the write segment in the RPC-over-RDMA header to reflect the extra
pad bytes.

The Reply chunk is also a write chunk, but the server does not use
send_write_chunks() to send the Reply chunk. That's OK in this case:
the server Upper Layer typically marshals the Reply chunk contents
in a single contiguous buffer, without a separate tail for the XDR
pad.

The comments and the variable naming refer to "chunks" but what is
really meant is "segments." The existing code sends only one
xdr_write_chunk per RPC reply.

The fix assumes this as well. When the XDR pad in the first write
chunk is reached, the assumption is the Write list is complete and
send_write_chunks() returns.

That will remain a valid assumption until the server Upper Layer can
support multiple bulk payload results per RPC.

Signed-off-by: Chuck Lever <[email protected]>
---
net/sunrpc/xprtrdma/svc_rdma_sendto.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index 1dfae83..6c48901 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -342,6 +342,13 @@ static int send_write_chunks(struct svcxprt_rdma *xprt,
arg_ch->rs_handle,
arg_ch->rs_offset,
write_len);
+
+ /* Do not send XDR pad bytes */
+ if (chunk_no && write_len < 4) {
+ chunk_no++;
+ break;
+ }
+
chunk_off = 0;
while (write_len) {
ret = send_write(xprt, rqstp,

2015-11-12 19:13:04

by J. Bruce Fields

Subject: Re: [PATCH] svcrdma: Do not send XDR roundup bytes for a write chunk

Thanks, applying.

On Thu, Nov 12, 2015 at 09:44:33AM -0500, Chuck Lever wrote:
> Minor optimization:

Based on that I'm queueing it up for 4.5--let me know if that causes
some problem.

--b.

> when dealing with write chunk XDR roundup, do
> not post a Write WR for the zero bytes in the pad. Simply update
> the write segment in the RPC-over-RDMA header to reflect the extra
> pad bytes.
>
> The Reply chunk is also a write chunk, but the server does not use
> send_write_chunks() to send the Reply chunk. That's OK in this case:
> the server Upper Layer typically marshals the Reply chunk contents
> in a single contiguous buffer, without a separate tail for the XDR
> pad.
>
> The comments and the variable naming refer to "chunks" but what is
> really meant is "segments." The existing code sends only one
> xdr_write_chunk per RPC reply.
>
> The fix assumes this as well. When the XDR pad in the first write
> chunk is reached, the assumption is the Write list is complete and
> send_write_chunks() returns.
>
> That will remain a valid assumption until the server Upper Layer can
> support multiple bulk payload results per RPC.
>
> Signed-off-by: Chuck Lever <[email protected]>
> ---
> net/sunrpc/xprtrdma/svc_rdma_sendto.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> index 1dfae83..6c48901 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> @@ -342,6 +342,13 @@ static int send_write_chunks(struct svcxprt_rdma *xprt,
> arg_ch->rs_handle,
> arg_ch->rs_offset,
> write_len);
> +
> + /* Do not send XDR pad bytes */
> + if (chunk_no && write_len < 4) {
> + chunk_no++;
> + break;
> + }
> +
> chunk_off = 0;
> while (write_len) {
> ret = send_write(xprt, rqstp,