From: Trond Myklebust trond.myklebust@hammerspace.com
commit ea7a1019d8baf8503ecd6e3ec8436dec283569e6 upstream.
The premise of commit 6f9f17287e78 ("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 6f9f17287e78 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 --- net/sunrpc/xprt.c | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-)
--- a/net/sunrpc/xprt.c +++ b/net/sunrpc/xprt.c @@ -1603,15 +1603,14 @@ 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); @@ -1619,13 +1618,16 @@ 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); }