From 9c40c49f145f8999ecbf81683aeb31d92b61b966 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Thu, 15 Sep 2016 10:55:53 -0400 Subject: xprtrdma: Initialize separate RPC call and reply buffers RPC-over-RDMA needs to separate its RPC call and reply buffers. o When an RPC Call is sent, rq_snd_buf is DMA mapped for an RDMA Send operation using DMA_TO_DEVICE o If the client expects a large RPC reply, it DMA maps rq_rcv_buf as part of a Reply chunk using DMA_FROM_DEVICE The two mappings are for data movement in opposite directions. DMA-API.txt suggests that if these mappings share a DMA cacheline, bad things can happen. This could occur in the final bytes of rq_snd_buf and the first bytes of rq_rcv_buf if the two buffers happen to share a DMA cacheline. On x86_64 the cacheline size is typically 8 bytes, and RPC call messages are usually much smaller than the send buffer, so this hasn't been a noticeable problem. But the DMA cacheline size can be larger on other platforms. Also, often rq_rcv_buf starts most of the way into a page, thus an additional RDMA segment is needed to map and register the end of that buffer. Try to avoid that scenario to reduce the cost of registering and invalidating Reply chunks. Instead of carrying a single regbuf that covers both rq_snd_buf and rq_rcv_buf, each struct rpcrdma_req now carries one regbuf for rq_snd_buf and one regbuf for rq_rcv_buf. Some incidental changes worth noting: - To clear out some spaghetti, refactor xprt_rdma_allocate. - The value stored in rg_size is the same as the value stored in the iov.length field, so eliminate rg_size Signed-off-by: Chuck Lever Signed-off-by: Anna Schumaker --- net/sunrpc/xprtrdma/xprt_rdma.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'net/sunrpc/xprtrdma/xprt_rdma.h') diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h index 484855eddb85..444f6370d46c 100644 --- a/net/sunrpc/xprtrdma/xprt_rdma.h +++ b/net/sunrpc/xprtrdma/xprt_rdma.h @@ -112,7 +112,6 @@ struct rpcrdma_ep { */ struct rpcrdma_regbuf { - size_t rg_size; struct ib_sge rg_iov; __be32 rg_base[0] __attribute__ ((aligned(256))); }; @@ -285,8 +284,9 @@ struct rpcrdma_req { struct rpcrdma_buffer *rl_buffer; struct rpcrdma_rep *rl_reply;/* holder for reply buffer */ struct ib_sge rl_send_iov[RPCRDMA_MAX_IOVS]; - struct rpcrdma_regbuf *rl_rdmabuf; - struct rpcrdma_regbuf *rl_sendbuf; + struct rpcrdma_regbuf *rl_rdmabuf; /* xprt header */ + struct rpcrdma_regbuf *rl_sendbuf; /* rq_snd_buf */ + struct rpcrdma_regbuf *rl_recvbuf; /* rq_rcv_buf */ struct ib_cqe rl_cqe; struct list_head rl_all; -- cgit v1.2.3