SUNRPC: Mitigate cond_resched() in xprt_transmit()

[ 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@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 5a8e47bbfb9f45a925a6eb2fd891fb917a1e09a4..13fbc2dd4196a16fc4c5370c3a797031b20ecebf 100644 (file)
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1520,10 +1520,13 @@ 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);
@@ -1531,7 +1534,6 @@ 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) {