[PATCH AUTOSEL 5.4 42/80] SUNRPC: Mitigate cond_resched() in xprt_transmit()

From: Sasha Levin
Date: Mon Oct 26 2020 - 20:03:38 EST


From: Chuck Lever <chuck.lever@xxxxxxxxxx>

[ Upstream commit 6f9f17287e78e5049931af2037b15b26d134a32a ]

The original purpose of this expensive call is to prevent a long
queue of requests from blocking other work.

The cond_resched() call is unnecessary after just a single send
operation.

For longer queues, instead of invoking the kernel scheduler, simply
release the transport send lock and return to the RPC scheduler.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/sunrpc/xprt.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 41df4c507193b..a6fee86f400ec 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1503,10 +1503,13 @@ xprt_transmit(struct rpc_task *task)
{
struct rpc_rqst *next, *req = task->tk_rqstp;
struct rpc_xprt *xprt = req->rq_xprt;
- int status;
+ int counter, status;

spin_lock(&xprt->queue_lock);
+ counter = 0;
while (!list_empty(&xprt->xmit_queue)) {
+ if (++counter == 20)
+ break;
next = list_first_entry(&xprt->xmit_queue,
struct rpc_rqst, rq_xmit);
xprt_pin_rqst(next);
@@ -1514,7 +1517,6 @@ xprt_transmit(struct rpc_task *task)
status = xprt_request_transmit(next, task);
if (status == -EBADMSG && next != req)
status = 0;
- cond_resched();
spin_lock(&xprt->queue_lock);
xprt_unpin_rqst(next);
if (status == 0) {
--
2.25.1