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svcrdma: Remove BH-disabled spin locking in svc_rdma_send()

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svcrdma's current SQ accounting algorithm takes sc_lock and disables
bottom-halves while posting all RDMA Read, Write, and Send WRs.

This is relatively heavyweight serialization. And note that Write and
Send are already fully serialized by the xpt_mutex.

Using a single atomic_t should be all that is necessary to guarantee
that ib_post_send() is called only when there is enough space on the
send queue. This is what the other RDMA-enabled storage targets do.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Chuck Lever 2016-11-29 11:04:50 -05:00 committed by J. Bruce Fields
parent 5fdca65314
commit e4eb42cecc
3 changed files with 17 additions and 17 deletions
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2
include/linux/sunrpc/svc_rdma.h
View File

@ -139,7 +139,7 @@ struct svcxprt_rdma {
int sc_max_sge_rd; /* max sge for read target */
bool sc_snd_w_inv; /* OK to use Send With Invalidate */
atomic_t sc_sq_count; /* Number of SQ WR on queue */
atomic_t sc_sq_avail; /* SQEs ready to be consumed */
unsigned int sc_sq_depth; /* Depth of SQ */
unsigned int sc_rq_depth; /* Depth of RQ */
u32 sc_max_requests; /* Forward credits */

7
net/sunrpc/xprtrdma/svc_rdma_sendto.c
View File

@ -594,7 +594,12 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
goto err0;
inline_bytes = rqstp->rq_res.len;
/* Create the RDMA response header */
/* Create the RDMA response header. xprt->xpt_mutex,
* acquired in svc_send(), serializes RPC replies. The
* code path below that inserts the credit grant value
* into each transport header runs only inside this
* critical section.
*/
ret = -ENOMEM;
res_page = alloc_page(GFP_KERNEL);
if (!res_page)

25
net/sunrpc/xprtrdma/svc_rdma_transport.c
View File

@ -434,7 +434,7 @@ static void svc_rdma_send_wc_common(struct svcxprt_rdma *xprt,
goto err;
out:
atomic_dec(&xprt->sc_sq_count);
atomic_inc(&xprt->sc_sq_avail);
wake_up(&xprt->sc_send_wait);
return;
@ -1008,6 +1008,7 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
newxprt->sc_rq_depth = newxprt->sc_max_requests +
newxprt->sc_max_bc_requests;
newxprt->sc_sq_depth = RPCRDMA_SQ_DEPTH_MULT * newxprt->sc_rq_depth;
atomic_set(&newxprt->sc_sq_avail, newxprt->sc_sq_depth);
if (!svc_rdma_prealloc_ctxts(newxprt))
goto errout;
@ -1333,15 +1334,13 @@ int svc_rdma_send(struct svcxprt_rdma *xprt, struct ib_send_wr *wr)
/* If the SQ is full, wait until an SQ entry is available */
while (1) {
spin_lock_bh(&xprt->sc_lock);
if (xprt->sc_sq_depth < atomic_read(&xprt->sc_sq_count) + wr_count) {
spin_unlock_bh(&xprt->sc_lock);
if ((atomic_sub_return(wr_count, &xprt->sc_sq_avail) < 0)) {
atomic_inc(&rdma_stat_sq_starve);
/* Wait until SQ WR available if SQ still full */
atomic_add(wr_count, &xprt->sc_sq_avail);
wait_event(xprt->sc_send_wait,
atomic_read(&xprt->sc_sq_count) <
xprt->sc_sq_depth);
atomic_read(&xprt->sc_sq_avail) > wr_count);
if (test_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags))
return -ENOTCONN;
continue;
@ -1351,21 +1350,17 @@ int svc_rdma_send(struct svcxprt_rdma *xprt, struct ib_send_wr *wr)
svc_xprt_get(&xprt->sc_xprt);
/* Bump used SQ WR count and post */
atomic_add(wr_count, &xprt->sc_sq_count);
ret = ib_post_send(xprt->sc_qp, wr, &bad_wr);
if (ret) {
set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
atomic_sub(wr_count, &xprt->sc_sq_count);
for (i = 0; i < wr_count; i ++)
svc_xprt_put(&xprt->sc_xprt);
dprintk("svcrdma: failed to post SQ WR rc=%d, "
"sc_sq_count=%d, sc_sq_depth=%d\n",
ret, atomic_read(&xprt->sc_sq_count),
xprt->sc_sq_depth);
}
spin_unlock_bh(&xprt->sc_lock);
if (ret)
dprintk("svcrdma: failed to post SQ WR rc=%d\n", ret);
dprintk(" sc_sq_avail=%d, sc_sq_depth=%d\n",
atomic_read(&xprt->sc_sq_avail),
xprt->sc_sq_depth);
wake_up(&xprt->sc_send_wait);
}
break;
}
return ret;