[PATCH v1 06/14] xprtrdma: Acquire FMRs in rpcrdma_fmr_register_external()

Chuck Lever
2015-05-04T17:57:39Z

Acquiring 64 FMRs in rpcrdma_buffer_get() while holding the buffer
pool lock is expensive, and unnecessary because FMR mode can
transfer up to a 1MB payload using just a single ib_fmr.

Instead, acquire ib_fmrs one-at-a-time as chunks are registered, and
return them to rb_mws immediately during deregistration.

Transport reset is now unneeded for FMR. Each FMR is recovered
synchronously when its RPC is retransmitted.

Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
---
net/sunrpc/xprtrdma/fmr_ops.c | 64 +++++++++++++++++++++++++++++++----------
net/sunrpc/xprtrdma/verbs.c | 26 -----------------
2 files changed, 48 insertions(+), 42 deletions(-)

diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fmr_ops.c
index 0a96155..ad0055b 100644
--- a/net/sunrpc/xprtrdma/fmr_ops.c
+++ b/net/sunrpc/xprtrdma/fmr_ops.c
@@ -11,6 +11,21 @@
* can take tens of usecs to complete.
*/

+/* Normal operation
+ *
+ * A Memory Region is prepared for RDMA READ or WRITE using the
+ * ib_map_phys_fmr verb (fmr_op_map). When the RDMA operation is
+ * finished, the Memory Region is unmapped using the ib_unmap_fmr
+ * verb (fmr_op_unmap).
+ */
+
+/* Transport recovery
+ *
+ * After a transport reconnect, fmr_op_map re-uses the MR already
+ * allocated for the RPC, but generates a fresh rkey then maps the
+ * MR again. This process is synchronous.
+ */
+
#include "xprt_rdma.h"

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
@@ -77,6 +92,15 @@ out_fmr_err:
return rc;
}

+static int
+__fmr_unmap(struct rpcrdma_mw *r)
+{
+ LIST_HEAD(l);
+
+ list_add(&r->r.fmr->list, &l);
+ return ib_unmap_fmr(&l);
+}
+
/* Use the ib_map_phys_fmr() verb to register a memory region
* for remote access via RDMA READ or RDMA WRITE.
*/
@@ -88,9 +112,22 @@ fmr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
struct ib_device *device = ia->ri_device;
enum dma_data_direction direction = rpcrdma_data_dir(writing);
struct rpcrdma_mr_seg *seg1 = seg;
- struct rpcrdma_mw *mw = seg1->rl_mw;
u64 physaddrs[RPCRDMA_MAX_DATA_SEGS];
int len, pageoff, i, rc;
+ struct rpcrdma_mw *mw;
+
+ mw = seg1->rl_mw;
+ seg1->rl_mw = NULL;
+ if (!mw) {
+ mw = rpcrdma_get_mw(r_xprt);
+ if (!mw)
+ return -ENOMEM;
+ } else {
+ /* this is a retransmit; generate a fresh rkey */
+ rc = __fmr_unmap(mw);
+ if (rc)
+ return rc;
+ }

pageoff = offset_in_page(seg1->mr_offset);
seg1->mr_offset -= pageoff; /* start of page */
@@ -114,6 +151,7 @@ fmr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
if (rc)
goto out_maperr;

+ seg1->rl_mw = mw;
seg1->mr_rkey = mw->r.fmr->rkey;
seg1->mr_base = seg1->mr_dma + pageoff;
seg1->mr_nsegs = i;
@@ -137,18 +175,24 @@ fmr_op_unmap(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg)
{
struct rpcrdma_ia *ia = &r_xprt->rx_ia;
struct rpcrdma_mr_seg *seg1 = seg;
+ struct rpcrdma_mw *mw = seg1->rl_mw;
int rc, nsegs = seg->mr_nsegs;
- LIST_HEAD(l);

- list_add(&seg1->rl_mw->r.fmr->list, &l);
- rc = ib_unmap_fmr(&l);
+ dprintk("RPC: %s: FMR %p\n", __func__, mw);
+
+ seg1->rl_mw = NULL;
while (seg1->mr_nsegs--)
rpcrdma_unmap_one(ia->ri_device, seg++);
+ rc = __fmr_unmap(mw);
if (rc)
goto out_err;
+ rpcrdma_put_mw(r_xprt, mw);
return nsegs;

out_err:
+ /* The FMR is abandoned, but remains in rb_all. fmr_op_destroy
+ * will attempt to release it when the transport is destroyed.
+ */
dprintk("RPC: %s: ib_unmap_fmr status %i\n", __func__, rc);
return nsegs;
}
@@ -161,18 +205,6 @@ out_err:
static void
fmr_op_reset(struct rpcrdma_xprt *r_xprt)
{
- struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
- struct rpcrdma_mw *r;
- LIST_HEAD(list);
- int rc;
-
- list_for_each_entry(r, &buf->rb_all, mw_all)
- list_add(&r->r.fmr->list, &list);
-
- rc = ib_unmap_fmr(&list);
- if (rc)
- dprintk("RPC: %s: ib_unmap_fmr failed %i\n",
- __func__, rc);
}

static void
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index c21329e..8a43c7ef 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1331,28 +1331,6 @@ rpcrdma_buffer_get_frmrs(struct rpcrdma_req *req, struct rpcrdma_buffer *buf,
return NULL;
}

-static struct rpcrdma_req *
-rpcrdma_buffer_get_fmrs(struct rpcrdma_req *req, struct rpcrdma_buffer *buf)
-{
- struct rpcrdma_mw *r;
- int i;
-
- i = RPCRDMA_MAX_SEGS - 1;
- while (!list_empty(&buf->rb_mws)) {
- r = list_entry(buf->rb_mws.next,
- struct rpcrdma_mw, mw_list);
- list_del(&r->mw_list);
- req->rl_segments[i].rl_mw = r;
- if (unlikely(i-- == 0))
- return req; /* Success */
- }
-
- /* Not enough entries on rb_mws for this req */
- rpcrdma_buffer_put_sendbuf(req, buf);
- rpcrdma_buffer_put_mrs(req, buf);
- return NULL;
-}
-
/*
* Get a set of request/reply buffers.
*
@@ -1394,9 +1372,6 @@ rpcrdma_buffer_get(struct rpcrdma_buffer *buffers)
case RPCRDMA_FRMR:
req = rpcrdma_buffer_get_frmrs(req, buffers, &stale);
break;
- case RPCRDMA_MTHCAFMR:
- req = rpcrdma_buffer_get_fmrs(req, buffers);
- break;
default:
break;
}
@@ -1421,7 +1396,6 @@ rpcrdma_buffer_put(struct rpcrdma_req *req)
rpcrdma_buffer_put_sendbuf(req, buffers);
switch (ia->ri_memreg_strategy) {
case RPCRDMA_FRMR:
- case RPCRDMA_MTHCAFMR:
rpcrdma_buffer_put_mrs(req, buffers);
break;