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xprtrdma: Remove logic that constructs RDMA_MSGP type calls
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RDMA_MSGP type calls insert a zero pad in the middle of the RPC
message to align the RPC request's data payload to the server's
alignment preferences. A server can then "page flip" the payload
into place to avoid a data copy in certain circumstances. However:

1. The client has to have a priori knowledge of the server's
   preferred alignment

2. Requests eligible for RDMA_MSGP are requests that are small
   enough to have been sent inline, and convey a data payload
   at the _end_ of the RPC message

Today 1. is done with a sysctl, and is a global setting that is
copied during mount. Linux does not support CCP to query the
server's preferences (RFC 5666, Section 6).

A small-ish NFSv3 WRITE might use RDMA_MSGP, but no NFSv4
compound fits bullet 2.

Thus the Linux client currently leaves RDMA_MSGP disabled. The
Linux server handles RDMA_MSGP, but does not use any special
page flipping, so it confers no benefit.

Clean up the marshaling code by removing the logic that constructs
RDMA_MSGP type calls. This also reduces the maximum send iovec size
from four to just two elements.

/proc/sys/sunrpc/rdma_inline_write_padding is a kernel API, and
thus is left in place.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Devesh Sharma <devesh.sharma@avagotech.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
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Chuck Lever authored and Anna Schumaker committed Aug 5, 2015
1 parent d1ed857 commit b3221d6
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Showing 3 changed files with 51 additions and 107 deletions.
92 changes: 24 additions & 68 deletions net/sunrpc/xprtrdma/rpc_rdma.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -297,8 +297,7 @@ rpcrdma_create_chunks(struct rpc_rqst *rqst, struct xdr_buf *target,
* pre-registered memory buffer for this request. For small amounts
* of data, this is efficient. The cutoff value is tunable.
*/
static int
rpcrdma_inline_pullup(struct rpc_rqst *rqst, int pad)
static void rpcrdma_inline_pullup(struct rpc_rqst *rqst)
{
int i, npages, curlen;
int copy_len;
Expand All @@ -310,16 +309,9 @@ rpcrdma_inline_pullup(struct rpc_rqst *rqst, int pad)
destp = rqst->rq_svec[0].iov_base;
curlen = rqst->rq_svec[0].iov_len;
destp += curlen;
/*
* Do optional padding where it makes sense. Alignment of write
* payload can help the server, if our setting is accurate.
*/
pad -= (curlen + 36/*sizeof(struct rpcrdma_msg_padded)*/);
if (pad < 0 || rqst->rq_slen - curlen < RPCRDMA_INLINE_PAD_THRESH)
pad = 0; /* don't pad this request */

dprintk("RPC: %s: pad %d destp 0x%p len %d hdrlen %d\n",
__func__, pad, destp, rqst->rq_slen, curlen);
dprintk("RPC: %s: destp 0x%p len %d hdrlen %d\n",
__func__, destp, rqst->rq_slen, curlen);

copy_len = rqst->rq_snd_buf.page_len;

Expand Down Expand Up @@ -355,7 +347,6 @@ rpcrdma_inline_pullup(struct rpc_rqst *rqst, int pad)
page_base = 0;
}
/* header now contains entire send message */
return pad;
}

/*
Expand All @@ -380,7 +371,7 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
char *base;
size_t rpclen, padlen;
size_t rpclen;
ssize_t hdrlen;
enum rpcrdma_chunktype rtype, wtype;
struct rpcrdma_msg *headerp;
Expand Down Expand Up @@ -458,7 +449,6 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
}

hdrlen = RPCRDMA_HDRLEN_MIN;
padlen = 0;

/*
* Pull up any extra send data into the preregistered buffer.
Expand All @@ -467,43 +457,24 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
*/
if (rtype == rpcrdma_noch) {

padlen = rpcrdma_inline_pullup(rqst,
RPCRDMA_INLINE_PAD_VALUE(rqst));

if (padlen) {
headerp->rm_type = rdma_msgp;
headerp->rm_body.rm_padded.rm_align =
cpu_to_be32(RPCRDMA_INLINE_PAD_VALUE(rqst));
headerp->rm_body.rm_padded.rm_thresh =
cpu_to_be32(RPCRDMA_INLINE_PAD_THRESH);
headerp->rm_body.rm_padded.rm_pempty[0] = xdr_zero;
headerp->rm_body.rm_padded.rm_pempty[1] = xdr_zero;
headerp->rm_body.rm_padded.rm_pempty[2] = xdr_zero;
hdrlen += 2 * sizeof(u32); /* extra words in padhdr */
if (wtype != rpcrdma_noch) {
dprintk("RPC: %s: invalid chunk list\n",
__func__);
return -EIO;
}
} else {
headerp->rm_body.rm_nochunks.rm_empty[0] = xdr_zero;
headerp->rm_body.rm_nochunks.rm_empty[1] = xdr_zero;
headerp->rm_body.rm_nochunks.rm_empty[2] = xdr_zero;
/* new length after pullup */
rpclen = rqst->rq_svec[0].iov_len;
/*
* Currently we try to not actually use read inline.
* Reply chunks have the desirable property that
* they land, packed, directly in the target buffers
* without headers, so they require no fixup. The
* additional RDMA Write op sends the same amount
* of data, streams on-the-wire and adds no overhead
* on receive. Therefore, we request a reply chunk
* for non-writes wherever feasible and efficient.
*/
if (wtype == rpcrdma_noch)
wtype = rpcrdma_replych;
}
rpcrdma_inline_pullup(rqst);

headerp->rm_body.rm_nochunks.rm_empty[0] = xdr_zero;
headerp->rm_body.rm_nochunks.rm_empty[1] = xdr_zero;
headerp->rm_body.rm_nochunks.rm_empty[2] = xdr_zero;
/* new length after pullup */
rpclen = rqst->rq_svec[0].iov_len;
/* Currently we try to not actually use read inline.
* Reply chunks have the desirable property that
* they land, packed, directly in the target buffers
* without headers, so they require no fixup. The
* additional RDMA Write op sends the same amount
* of data, streams on-the-wire and adds no overhead
* on receive. Therefore, we request a reply chunk
* for non-writes wherever feasible and efficient.
*/
if (wtype == rpcrdma_noch)
wtype = rpcrdma_replych;
}

if (rtype != rpcrdma_noch) {
Expand All @@ -518,9 +489,9 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
if (hdrlen < 0)
return hdrlen;

dprintk("RPC: %s: %s: hdrlen %zd rpclen %zd padlen %zd"
dprintk("RPC: %s: %s: hdrlen %zd rpclen %zd"
" headerp 0x%p base 0x%p lkey 0x%x\n",
__func__, transfertypes[wtype], hdrlen, rpclen, padlen,
__func__, transfertypes[wtype], hdrlen, rpclen,
headerp, base, rdmab_lkey(req->rl_rdmabuf));

/*
Expand All @@ -539,21 +510,6 @@ rpcrdma_marshal_req(struct rpc_rqst *rqst)
req->rl_send_iov[1].lkey = rdmab_lkey(req->rl_sendbuf);

req->rl_niovs = 2;

if (padlen) {
struct rpcrdma_ep *ep = &r_xprt->rx_ep;

req->rl_send_iov[2].addr = rdmab_addr(ep->rep_padbuf);
req->rl_send_iov[2].length = padlen;
req->rl_send_iov[2].lkey = rdmab_lkey(ep->rep_padbuf);

req->rl_send_iov[3].addr = req->rl_send_iov[1].addr + rpclen;
req->rl_send_iov[3].length = rqst->rq_slen - rpclen;
req->rl_send_iov[3].lkey = rdmab_lkey(req->rl_sendbuf);

req->rl_niovs = 4;
}

return 0;
}

Expand Down
47 changes: 17 additions & 30 deletions net/sunrpc/xprtrdma/verbs.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -605,6 +605,12 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
struct ib_cq_init_attr cq_attr = {};
int rc, err;

if (devattr->max_sge < RPCRDMA_MAX_IOVS) {
dprintk("RPC: %s: insufficient sge's available\n",
__func__);
return -ENOMEM;
}

/* check provider's send/recv wr limits */
if (cdata->max_requests > devattr->max_qp_wr)
cdata->max_requests = devattr->max_qp_wr;
Expand All @@ -617,23 +623,13 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
if (rc)
return rc;
ep->rep_attr.cap.max_recv_wr = cdata->max_requests;
ep->rep_attr.cap.max_send_sge = (cdata->padding ? 4 : 2);
ep->rep_attr.cap.max_send_sge = RPCRDMA_MAX_IOVS;
ep->rep_attr.cap.max_recv_sge = 1;
ep->rep_attr.cap.max_inline_data = 0;
ep->rep_attr.sq_sig_type = IB_SIGNAL_REQ_WR;
ep->rep_attr.qp_type = IB_QPT_RC;
ep->rep_attr.port_num = ~0;

if (cdata->padding) {
ep->rep_padbuf = rpcrdma_alloc_regbuf(ia, cdata->padding,
GFP_KERNEL);
if (IS_ERR(ep->rep_padbuf)) {
rc = PTR_ERR(ep->rep_padbuf);
goto out0;
}
} else
ep->rep_padbuf = NULL;

dprintk("RPC: %s: requested max: dtos: send %d recv %d; "
"iovs: send %d recv %d\n",
__func__,
Expand Down Expand Up @@ -716,8 +712,6 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
dprintk("RPC: %s: ib_destroy_cq returned %i\n",
__func__, err);
out1:
rpcrdma_free_regbuf(ia, ep->rep_padbuf);
out0:
if (ia->ri_dma_mr)
ib_dereg_mr(ia->ri_dma_mr);
return rc;
Expand Down Expand Up @@ -746,8 +740,6 @@ rpcrdma_ep_destroy(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia)
ia->ri_id->qp = NULL;
}

rpcrdma_free_regbuf(ia, ep->rep_padbuf);

rpcrdma_clean_cq(ep->rep_attr.recv_cq);
rc = ib_destroy_cq(ep->rep_attr.recv_cq);
if (rc)
Expand Down Expand Up @@ -1279,9 +1271,11 @@ rpcrdma_ep_post(struct rpcrdma_ia *ia,
struct rpcrdma_ep *ep,
struct rpcrdma_req *req)
{
struct ib_device *device = ia->ri_device;
struct ib_send_wr send_wr, *send_wr_fail;
struct rpcrdma_rep *rep = req->rl_reply;
int rc;
struct ib_sge *iov = req->rl_send_iov;
int i, rc;

if (rep) {
rc = rpcrdma_ep_post_recv(ia, ep, rep);
Expand All @@ -1292,22 +1286,15 @@ rpcrdma_ep_post(struct rpcrdma_ia *ia,

send_wr.next = NULL;
send_wr.wr_id = RPCRDMA_IGNORE_COMPLETION;
send_wr.sg_list = req->rl_send_iov;
send_wr.sg_list = iov;
send_wr.num_sge = req->rl_niovs;
send_wr.opcode = IB_WR_SEND;
if (send_wr.num_sge == 4) /* no need to sync any pad (constant) */
ib_dma_sync_single_for_device(ia->ri_device,
req->rl_send_iov[3].addr,
req->rl_send_iov[3].length,
DMA_TO_DEVICE);
ib_dma_sync_single_for_device(ia->ri_device,
req->rl_send_iov[1].addr,
req->rl_send_iov[1].length,
DMA_TO_DEVICE);
ib_dma_sync_single_for_device(ia->ri_device,
req->rl_send_iov[0].addr,
req->rl_send_iov[0].length,
DMA_TO_DEVICE);

for (i = 0; i < send_wr.num_sge; i++)
ib_dma_sync_single_for_device(device, iov[i].addr,
iov[i].length, DMA_TO_DEVICE);
dprintk("RPC: %s: posting %d s/g entries\n",
__func__, send_wr.num_sge);

if (DECR_CQCOUNT(ep) > 0)
send_wr.send_flags = 0;
Expand Down
19 changes: 10 additions & 9 deletions net/sunrpc/xprtrdma/xprt_rdma.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,6 @@ struct rpcrdma_ep {
int rep_connected;
struct ib_qp_init_attr rep_attr;
wait_queue_head_t rep_connect_wait;
struct rpcrdma_regbuf *rep_padbuf;
struct rdma_conn_param rep_remote_cma;
struct sockaddr_storage rep_remote_addr;
struct delayed_work rep_connect_worker;
Expand Down Expand Up @@ -255,16 +254,18 @@ struct rpcrdma_mr_seg { /* chunk descriptors */
char *mr_offset; /* kva if no page, else offset */
};

#define RPCRDMA_MAX_IOVS (2)

struct rpcrdma_req {
unsigned int rl_niovs; /* 0, 2 or 4 */
unsigned int rl_nchunks; /* non-zero if chunks */
unsigned int rl_connect_cookie; /* retry detection */
struct rpcrdma_buffer *rl_buffer; /* home base for this structure */
unsigned int rl_niovs;
unsigned int rl_nchunks;
unsigned int rl_connect_cookie;
struct rpcrdma_buffer *rl_buffer;
struct rpcrdma_rep *rl_reply;/* holder for reply buffer */
struct ib_sge rl_send_iov[4]; /* for active requests */
struct rpcrdma_regbuf *rl_rdmabuf;
struct rpcrdma_regbuf *rl_sendbuf;
struct rpcrdma_mr_seg rl_segments[RPCRDMA_MAX_SEGS];
struct ib_sge rl_send_iov[RPCRDMA_MAX_IOVS];
struct rpcrdma_regbuf *rl_rdmabuf;
struct rpcrdma_regbuf *rl_sendbuf;
struct rpcrdma_mr_seg rl_segments[RPCRDMA_MAX_SEGS];
};

static inline struct rpcrdma_req *
Expand Down

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