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SUNRPC: Improve ordering of transport processing

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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>
This commit is contained in:
Trond Myklebust 2017-10-10 17:31:43 -04:00 committed by J. Bruce Fields
parent 95da1b3a5a
commit 22700f3c6d
2 changed files with 31 additions and 70 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
include/linux/sunrpc/svc.h
View file

@ -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;

100
net/sunrpc/svc_xprt.c
View file

@ -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)