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SUNRPC: Improve ordering of transport processing
Since it can take a while before a specific thread gets scheduled, it is better to just implement a first come first served queue mechanism. That way, if a thread is already scheduled and is idle, it can pick up the work to do from the queue. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
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@ -46,6 +46,7 @@ struct svc_pool {
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struct svc_pool_stats sp_stats; /* statistics on pool operation */
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#define SP_TASK_PENDING (0) /* still work to do even if no
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* xprt is queued. */
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#define SP_CONGESTED (1)
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unsigned long sp_flags;
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} ____cacheline_aligned_in_smp;
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@ -380,7 +380,6 @@ void svc_xprt_do_enqueue(struct svc_xprt *xprt)
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struct svc_pool *pool;
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struct svc_rqst *rqstp = NULL;
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int cpu;
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bool queued = false;
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if (!svc_xprt_has_something_to_do(xprt))
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goto out;
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@ -401,58 +400,25 @@ void svc_xprt_do_enqueue(struct svc_xprt *xprt)
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atomic_long_inc(&pool->sp_stats.packets);
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redo_search:
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dprintk("svc: transport %p put into queue\n", xprt);
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spin_lock_bh(&pool->sp_lock);
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list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
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pool->sp_stats.sockets_queued++;
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spin_unlock_bh(&pool->sp_lock);
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/* find a thread for this xprt */
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rcu_read_lock();
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list_for_each_entry_rcu(rqstp, &pool->sp_all_threads, rq_all) {
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/* Do a lockless check first */
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if (test_bit(RQ_BUSY, &rqstp->rq_flags))
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if (test_and_set_bit(RQ_BUSY, &rqstp->rq_flags))
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continue;
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/*
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* Once the xprt has been queued, it can only be dequeued by
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* the task that intends to service it. All we can do at that
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* point is to try to wake this thread back up so that it can
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* do so.
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*/
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if (!queued) {
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spin_lock_bh(&rqstp->rq_lock);
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if (test_and_set_bit(RQ_BUSY, &rqstp->rq_flags)) {
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/* already busy, move on... */
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spin_unlock_bh(&rqstp->rq_lock);
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continue;
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}
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/* this one will do */
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rqstp->rq_xprt = xprt;
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svc_xprt_get(xprt);
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spin_unlock_bh(&rqstp->rq_lock);
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}
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rcu_read_unlock();
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atomic_long_inc(&pool->sp_stats.threads_woken);
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wake_up_process(rqstp->rq_task);
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put_cpu();
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goto out;
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}
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rcu_read_unlock();
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/*
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* We didn't find an idle thread to use, so we need to queue the xprt.
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* Do so and then search again. If we find one, we can't hook this one
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* up to it directly but we can wake the thread up in the hopes that it
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* will pick it up once it searches for a xprt to service.
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*/
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if (!queued) {
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queued = true;
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dprintk("svc: transport %p put into queue\n", xprt);
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spin_lock_bh(&pool->sp_lock);
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list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
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pool->sp_stats.sockets_queued++;
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spin_unlock_bh(&pool->sp_lock);
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goto redo_search;
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goto out_unlock;
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}
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set_bit(SP_CONGESTED, &pool->sp_flags);
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rqstp = NULL;
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out_unlock:
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rcu_read_unlock();
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put_cpu();
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out:
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trace_svc_xprt_do_enqueue(xprt, rqstp);
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@ -721,38 +687,25 @@ rqst_should_sleep(struct svc_rqst *rqstp)
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static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
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{
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struct svc_xprt *xprt;
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struct svc_pool *pool = rqstp->rq_pool;
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long time_left = 0;
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/* rq_xprt should be clear on entry */
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WARN_ON_ONCE(rqstp->rq_xprt);
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/* Normally we will wait up to 5 seconds for any required
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* cache information to be provided.
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*/
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rqstp->rq_chandle.thread_wait = 5*HZ;
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xprt = svc_xprt_dequeue(pool);
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if (xprt) {
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rqstp->rq_xprt = xprt;
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/* As there is a shortage of threads and this request
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* had to be queued, don't allow the thread to wait so
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* long for cache updates.
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*/
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rqstp->rq_chandle.thread_wait = 1*HZ;
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clear_bit(SP_TASK_PENDING, &pool->sp_flags);
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return xprt;
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}
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rqstp->rq_xprt = svc_xprt_dequeue(pool);
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if (rqstp->rq_xprt)
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goto out_found;
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/*
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* We have to be able to interrupt this wait
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* to bring down the daemons ...
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*/
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set_current_state(TASK_INTERRUPTIBLE);
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smp_mb__before_atomic();
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clear_bit(SP_CONGESTED, &pool->sp_flags);
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clear_bit(RQ_BUSY, &rqstp->rq_flags);
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smp_mb();
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smp_mb__after_atomic();
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if (likely(rqst_should_sleep(rqstp)))
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time_left = schedule_timeout(timeout);
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@ -761,13 +714,11 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
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try_to_freeze();
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spin_lock_bh(&rqstp->rq_lock);
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set_bit(RQ_BUSY, &rqstp->rq_flags);
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spin_unlock_bh(&rqstp->rq_lock);
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xprt = rqstp->rq_xprt;
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if (xprt != NULL)
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return xprt;
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smp_mb__after_atomic();
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rqstp->rq_xprt = svc_xprt_dequeue(pool);
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if (rqstp->rq_xprt)
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goto out_found;
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if (!time_left)
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atomic_long_inc(&pool->sp_stats.threads_timedout);
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@ -775,6 +726,15 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
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if (signalled() || kthread_should_stop())
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return ERR_PTR(-EINTR);
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return ERR_PTR(-EAGAIN);
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out_found:
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/* Normally we will wait up to 5 seconds for any required
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* cache information to be provided.
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*/
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if (!test_bit(SP_CONGESTED, &pool->sp_flags))
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rqstp->rq_chandle.thread_wait = 5*HZ;
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else
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rqstp->rq_chandle.thread_wait = 1*HZ;
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return rqstp->rq_xprt;
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}
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static void svc_add_new_temp_xprt(struct svc_serv *serv, struct svc_xprt *newxpt)
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