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@xxxxxxxxxxxxxxx>
---
include/linux/sunrpc/svc.h | 1 +
net/sunrpc/svc_xprt.c | 100 ++++++++++++++-------------------------------
2 files changed, 31 insertions(+), 70 deletions(-)
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 38f561b2dda3..23c4d6496aac 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -46,6 +46,7 @@ struct svc_pool {
struct svc_pool_stats sp_stats; /* statistics on pool operation */
#define SP_TASK_PENDING (0) /* still work to do even if no
* xprt is queued. */
+#define SP_CONGESTED (1)
unsigned long sp_flags;
} ____cacheline_aligned_in_smp;
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index d16a8b423c20..9b29c53281a8 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -380,7 +380,6 @@ void svc_xprt_do_enqueue(struct svc_xprt *xprt)
struct svc_pool *pool;
struct svc_rqst *rqstp = NULL;
int cpu;
- bool queued = false;
if (!svc_xprt_has_something_to_do(xprt))
goto out;
@@ -401,58 +400,25 @@ void svc_xprt_do_enqueue(struct svc_xprt *xprt)
atomic_long_inc(&pool->sp_stats.packets);
-redo_search:
+ dprintk("svc: transport %p put into queue\n", xprt);
+ spin_lock_bh(&pool->sp_lock);
+ list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
+ pool->sp_stats.sockets_queued++;
+ spin_unlock_bh(&pool->sp_lock);
+
/* find a thread for this xprt */
rcu_read_lock();
list_for_each_entry_rcu(rqstp, &pool->sp_all_threads, rq_all) {
- /* Do a lockless check first */
- if (test_bit(RQ_BUSY, &rqstp->rq_flags))
+ if (test_and_set_bit(RQ_BUSY, &rqstp->rq_flags))
continue;
-
- /*
- * Once the xprt has been queued, it can only be dequeued by
- * the task that intends to service it. All we can do at that
- * point is to try to wake this thread back up so that it can
- * do so.
- */
- if (!queued) {
- spin_lock_bh(&rqstp->rq_lock);
- if (test_and_set_bit(RQ_BUSY, &rqstp->rq_flags)) {
- /* already busy, move on... */
- spin_unlock_bh(&rqstp->rq_lock);
- continue;
- }
-
- /* this one will do */
- rqstp->rq_xprt = xprt;
- svc_xprt_get(xprt);
- spin_unlock_bh(&rqstp->rq_lock);
- }
- rcu_read_unlock();
-
atomic_long_inc(&pool->sp_stats.threads_woken);
wake_up_process(rqstp->rq_task);
- put_cpu();
- goto out;
- }
- rcu_read_unlock();
-
- /*
- * We didn't find an idle thread to use, so we need to queue the xprt.
- * Do so and then search again. If we find one, we can't hook this one
- * up to it directly but we can wake the thread up in the hopes that it
- * will pick it up once it searches for a xprt to service.
- */
- if (!queued) {
- queued = true;
- dprintk("svc: transport %p put into queue\n", xprt);
- spin_lock_bh(&pool->sp_lock);
- list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
- pool->sp_stats.sockets_queued++;
- spin_unlock_bh(&pool->sp_lock);
- goto redo_search;
+ goto out_unlock;
}
+ set_bit(SP_CONGESTED, &pool->sp_flags);
rqstp = NULL;
+out_unlock:
+ rcu_read_unlock();
put_cpu();
out:
trace_svc_xprt_do_enqueue(xprt, rqstp);
@@ -721,38 +687,25 @@ rqst_should_sleep(struct svc_rqst *rqstp)
static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
{
- struct svc_xprt *xprt;
struct svc_pool *pool = rqstp->rq_pool;
long time_left = 0;
/* rq_xprt should be clear on entry */
WARN_ON_ONCE(rqstp->rq_xprt);
- /* Normally we will wait up to 5 seconds for any required
- * cache information to be provided.
- */
- rqstp->rq_chandle.thread_wait = 5*HZ;
-
- xprt = svc_xprt_dequeue(pool);
- if (xprt) {
- rqstp->rq_xprt = xprt;
-
- /* As there is a shortage of threads and this request
- * had to be queued, don't allow the thread to wait so
- * long for cache updates.
- */
- rqstp->rq_chandle.thread_wait = 1*HZ;
- clear_bit(SP_TASK_PENDING, &pool->sp_flags);
- return xprt;
- }
+ rqstp->rq_xprt = svc_xprt_dequeue(pool);
+ if (rqstp->rq_xprt)
+ goto out_found;
/*
* We have to be able to interrupt this wait
* to bring down the daemons ...
*/
set_current_state(TASK_INTERRUPTIBLE);
+ smp_mb__before_atomic();
+ clear_bit(SP_CONGESTED, &pool->sp_flags);
clear_bit(RQ_BUSY, &rqstp->rq_flags);
- smp_mb();
+ smp_mb__after_atomic();
if (likely(rqst_should_sleep(rqstp)))
time_left = schedule_timeout(timeout);
@@ -761,13 +714,11 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
try_to_freeze();
- spin_lock_bh(&rqstp->rq_lock);
set_bit(RQ_BUSY, &rqstp->rq_flags);
- spin_unlock_bh(&rqstp->rq_lock);
-
- xprt = rqstp->rq_xprt;
- if (xprt != NULL)
- return xprt;
+ smp_mb__after_atomic();
+ rqstp->rq_xprt = svc_xprt_dequeue(pool);
+ if (rqstp->rq_xprt)
+ goto out_found;
if (!time_left)
atomic_long_inc(&pool->sp_stats.threads_timedout);
@@ -775,6 +726,15 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
if (signalled() || kthread_should_stop())
return ERR_PTR(-EINTR);
return ERR_PTR(-EAGAIN);
+out_found:
+ /* Normally we will wait up to 5 seconds for any required
+ * cache information to be provided.
+ */
+ if (!test_bit(SP_CONGESTED, &pool->sp_flags))
+ rqstp->rq_chandle.thread_wait = 5*HZ;
+ else
+ rqstp->rq_chandle.thread_wait = 1*HZ;
+ return rqstp->rq_xprt;
}
static void svc_add_new_temp_xprt(struct svc_serv *serv, struct svc_xprt *newxpt)
--
2.13.6
--
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