Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> points out that a steady
stream of CQ events could starve other work because of the boundless
loop pooling in rpcrdma_{send,recv}_poll().
Instead of a (potentially infinite) while loop, return after
collecting a budgeted number of completions.
Note that the total number of WCs that can be handled during one
upcall is RPCRDMA_WC_BUDGET * 2, since the handler polls once before
and once after re-enabling completion notifications.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
net/sunrpc/xprtrdma/verbs.c | 10 ++++++----
net/sunrpc/xprtrdma/xprt_rdma.h | 1 +
2 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index abb8d8d..d46bdee 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -165,8 +165,9 @@ static int
rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
{
struct ib_wc *wcs;
- int count, rc;
+ int budget, count, rc;
+ budget = RPCRDMA_WC_BUDGET / RPCRDMA_POLLSIZE;
do {
wcs = ep->rep_send_wcs;
@@ -177,7 +178,7 @@ rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
count = rc;
while (count-- > 0)
rpcrdma_sendcq_process_wc(wcs++);
- } while (rc == RPCRDMA_POLLSIZE);
+ } while (rc == RPCRDMA_POLLSIZE && --budget);
return 0;
}
@@ -254,8 +255,9 @@ static int
rpcrdma_recvcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
{
struct ib_wc *wcs;
- int count, rc;
+ int budget, count, rc;
+ budget = RPCRDMA_WC_BUDGET / RPCRDMA_POLLSIZE;
do {
wcs = ep->rep_recv_wcs;
@@ -266,7 +268,7 @@ rpcrdma_recvcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
count = rc;
while (count-- > 0)
rpcrdma_recvcq_process_wc(wcs++);
- } while (rc == RPCRDMA_POLLSIZE);
+ } while (rc == RPCRDMA_POLLSIZE && --budget);
return 0;
}
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index cb4c882..0c3b88e 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -74,6 +74,7 @@ struct rpcrdma_ia {
* RDMA Endpoint -- one per transport instance
*/
+#define RPCRDMA_WC_BUDGET (128)
#define RPCRDMA_POLLSIZE (16)
struct rpcrdma_ep {
--
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