SUNRPC: Count ingress RPC messages per svc_pool

svc_xprt_enqueue() can be costly, since it involves selecting and
waking up a process.

More than one enqueue is done per incoming RPC. For example,
svc_data_ready() enqueues, and so does svc_xprt_receive(). Also, if
an RPC message requires more than one call to ->recvfrom() to
receive it fully, each one of those calls does an enqueue.

To get a sense of the average number of transport enqueue operations
needed to process an incoming RPC message, re-use the "packets" pool
stat. Track the number of complete RPC messages processed by each
thread pool.
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svc.h

@@ -39,6 +39,7 @@ struct svc_pool {
 	struct list_head	sp_all_threads;	/* all server threads */
 
 	/* statistics on pool operation */
+	struct percpu_counter	sp_messages_arrived;
 	struct percpu_counter	sp_sockets_queued;
 	struct percpu_counter	sp_threads_woken;
 

net/sunrpc/svc.c

@@ -513,6 +513,7 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
 		INIT_LIST_HEAD(&pool->sp_all_threads);
 		spin_lock_init(&pool->sp_lock);
 
+		percpu_counter_init(&pool->sp_messages_arrived, 0, GFP_KERNEL);
 		percpu_counter_init(&pool->sp_sockets_queued, 0, GFP_KERNEL);
 		percpu_counter_init(&pool->sp_threads_woken, 0, GFP_KERNEL);
 	}
@@ -587,6 +588,7 @@ svc_destroy(struct kref *ref)
 	for (i = 0; i < serv->sv_nrpools; i++) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 
+		percpu_counter_destroy(&pool->sp_messages_arrived);
 		percpu_counter_destroy(&pool->sp_sockets_queued);
 		percpu_counter_destroy(&pool->sp_threads_woken);
 	}

net/sunrpc/svc_xprt.c

@@ -871,6 +871,7 @@ void svc_recv(struct svc_rqst *rqstp)
 
 	if (serv->sv_stats)
 		serv->sv_stats->netcnt++;
+	percpu_counter_inc(&rqstp->rq_pool->sp_messages_arrived);
 	rqstp->rq_stime = ktime_get();
 	svc_process(rqstp);
 out:
@@ -1420,7 +1421,7 @@ static int svc_pool_stats_show(struct seq_file *m, void *p)
 
 	seq_printf(m, "%u %llu %llu %llu 0\n",
 		   pool->sp_id,
-		   percpu_counter_sum_positive(&pool->sp_sockets_queued),
+		   percpu_counter_sum_positive(&pool->sp_messages_arrived),
 		   percpu_counter_sum_positive(&pool->sp_sockets_queued),
 		   percpu_counter_sum_positive(&pool->sp_threads_woken));