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SUNRPC: Partial revert of commit 6f9f17287e

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commit ea7a1019d8baf8503ecd6e3ec8436dec283569e6 upstream.

The premise of commit 6f9f17287e ("SUNRPC: Mitigate cond_resched() in
xprt_transmit()") was that cond_resched() is expensive and unnecessary
when there has been just a single send.
The point of cond_resched() is to ensure that tasks that should pre-empt
this one get a chance to do so when it is safe to do so. The code prior
to commit 6f9f17287e failed to take into account that it was keeping a
rpc_task pinned for longer than it needed to, and so rather than doing a
full revert, let's just move the cond_resched.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Trond Myklebust 2021-07-12 09:52:59 -04:00 committed by Greg Kroah-Hartman
parent c7a440cd30
commit d41f4d4dd7
1 changed files with 15 additions and 13 deletions
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28
net/sunrpc/xprt.c
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@ -1552,15 +1552,14 @@ xprt_transmit(struct rpc_task *task)
{
struct rpc_rqst *next, *req = task->tk_rqstp;
struct rpc_xprt *xprt = req->rq_xprt;
int counter, status;
int status;
spin_lock(&xprt->queue_lock);
counter = 0;
while (!list_empty(&xprt->xmit_queue)) {
if (++counter == 20)
for (;;) {
next = list_first_entry_or_null(&xprt->xmit_queue,
struct rpc_rqst, rq_xmit);
if (!next)
break;
next = list_first_entry(&xprt->xmit_queue,
struct rpc_rqst, rq_xmit);
xprt_pin_rqst(next);
spin_unlock(&xprt->queue_lock);
status = xprt_request_transmit(next, task);
@ -1568,13 +1567,16 @@ xprt_transmit(struct rpc_task *task)
status = 0;
spin_lock(&xprt->queue_lock);
xprt_unpin_rqst(next);
if (status == 0) {
if (!xprt_request_data_received(task) ||
test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
continue;
} else if (test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
task->tk_status = status;
break;
if (status < 0) {
if (test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
task->tk_status = status;
break;
}
/* Was @task transmitted, and has it received a reply? */
if (xprt_request_data_received(task) &&
!test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
break;
cond_resched_lock(&xprt->queue_lock);
}
spin_unlock(&xprt->queue_lock);
}