On Thu, Oct 19, 2017 at 03:38:17PM -0400, Chuck Lever wrote:
>
> > On Oct 10, 2017, at 1:31 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
> >
> > 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>
>
> Tested-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> Light performance testing, and a git software build / regression
> suite run on NFSv4.1. All on NFS/RDMA.
Thanks! And sorry for the slow response to this patch, the basic idea
sounds fine I just haven't found the time to understand the code change
yet!
--b.
>
>
> > ---
> > 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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>
> --
> Chuck Lever
>
>
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