From c05eecf636101dd4347b2d8fa457626bf0088e0a Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Fri, 30 Nov 2012 23:59:29 -0500 Subject: [PATCH] SUNRPC: Don't allow low priority tasks to pre-empt higher priority ones Currently, the priority queues attempt to be 'fair' to lower priority tasks by scheduling them after a certain number of higher priority tasks have run. The problem is that both the transport send queue and the NFSv4.1 session slot queue have strong ordering requirements. This patch therefore removes the fairness code in favour of strong ordering of task priorities. Signed-off-by: Trond Myklebust --- include/linux/sunrpc/sched.h | 1 - net/sunrpc/sched.c | 44 ++++++++++++++++++------------------ 2 files changed, 22 insertions(+), 23 deletions(-) diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h index dc0c3cc3ada3..b64f8eb0b973 100644 --- a/include/linux/sunrpc/sched.h +++ b/include/linux/sunrpc/sched.h @@ -192,7 +192,6 @@ struct rpc_wait_queue { pid_t owner; /* process id of last task serviced */ unsigned char maxpriority; /* maximum priority (0 if queue is not a priority queue) */ unsigned char priority; /* current priority */ - unsigned char count; /* # task groups remaining serviced so far */ unsigned char nr; /* # tasks remaining for cookie */ unsigned short qlen; /* total # tasks waiting in queue */ struct rpc_timer timer_list; diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index 1aefc9fef866..d17a704aaf5f 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -98,6 +98,23 @@ __rpc_add_timer(struct rpc_wait_queue *queue, struct rpc_task *task) list_add(&task->u.tk_wait.timer_list, &queue->timer_list.list); } +static void rpc_set_waitqueue_priority(struct rpc_wait_queue *queue, int priority) +{ + queue->priority = priority; +} + +static void rpc_set_waitqueue_owner(struct rpc_wait_queue *queue, pid_t pid) +{ + queue->owner = pid; + queue->nr = RPC_BATCH_COUNT; +} + +static void rpc_reset_waitqueue_priority(struct rpc_wait_queue *queue) +{ + rpc_set_waitqueue_priority(queue, queue->maxpriority); + rpc_set_waitqueue_owner(queue, 0); +} + /* * Add new request to a priority queue. */ @@ -109,9 +126,11 @@ static void __rpc_add_wait_queue_priority(struct rpc_wait_queue *queue, struct rpc_task *t; INIT_LIST_HEAD(&task->u.tk_wait.links); - q = &queue->tasks[queue_priority]; if (unlikely(queue_priority > queue->maxpriority)) - q = &queue->tasks[queue->maxpriority]; + queue_priority = queue->maxpriority; + if (queue_priority > queue->priority) + rpc_set_waitqueue_priority(queue, queue_priority); + q = &queue->tasks[queue_priority]; list_for_each_entry(t, q, u.tk_wait.list) { if (t->tk_owner == task->tk_owner) { list_add_tail(&task->u.tk_wait.list, &t->u.tk_wait.links); @@ -180,24 +199,6 @@ static void __rpc_remove_wait_queue(struct rpc_wait_queue *queue, struct rpc_tas task->tk_pid, queue, rpc_qname(queue)); } -static inline void rpc_set_waitqueue_priority(struct rpc_wait_queue *queue, int priority) -{ - queue->priority = priority; - queue->count = 1 << (priority * 2); -} - -static inline void rpc_set_waitqueue_owner(struct rpc_wait_queue *queue, pid_t pid) -{ - queue->owner = pid; - queue->nr = RPC_BATCH_COUNT; -} - -static inline void rpc_reset_waitqueue_priority(struct rpc_wait_queue *queue) -{ - rpc_set_waitqueue_priority(queue, queue->maxpriority); - rpc_set_waitqueue_owner(queue, 0); -} - static void __rpc_init_priority_wait_queue(struct rpc_wait_queue *queue, const char *qname, unsigned char nr_queues) { int i; @@ -464,8 +465,7 @@ static struct rpc_task *__rpc_find_next_queued_priority(struct rpc_wait_queue *q /* * Check if we need to switch queues. */ - if (--queue->count) - goto new_owner; + goto new_owner; } /*