linux-kernel - [PATCH AUTOSEL 5.8 071/132] SUNRPC: Mitigate cond_resched() in xprt

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Date:   Mon, 26 Oct 2020 19:51:03 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Chuck Lever <chuck.lever@...cle.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        Sasha Levin <sashal@...nel.org>, linux-nfs@...r.kernel.org,
        netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.8 071/132] SUNRPC: Mitigate cond_resched() in xprt_transmit()

From: Chuck Lever <chuck.lever@...cle.com>

[ 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@...cle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@...app.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 d5cc5db9dbf39..b44099958c8bb 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1511,10 +1511,13 @@ 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);
@@ -1522,7 +1525,6 @@ 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