padata: simplify serialization mechanism

We count the number of processed objects on a percpu basis,
so we need to go through all the percpu reorder queues to calculate
the sequence number of the next object that needs serialization.
This patch changes this to count the number of processed objects
global. So we can calculate the sequence number and the percpu
reorder queue of the next object that needs serialization without
searching through the percpu reorder queues. This avoids some
accesses to memory of foreign cpus.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 19 insertions, 52 deletions

diff --git a/kernel/padata.c b/kernel/padata.c
index ae8defc..450d67d 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -170,79 +170,47 @@ EXPORT_SYMBOL(padata_do_parallel);
  */
 static struct padata_priv *padata_get_next(struct parallel_data *pd)
 {
-	int cpu, num_cpus, empty, calc_seq_nr;
-	int seq_nr, next_nr, overrun, next_overrun;
+	int cpu, num_cpus;
+	int next_nr, next_index;
 	struct padata_queue *queue, *next_queue;
 	struct padata_priv *padata;
 	struct padata_list *reorder;
 
-	empty = 0;
-	next_nr = -1;
-	next_overrun = 0;
-	next_queue = NULL;
-
 	num_cpus = cpumask_weight(pd->cpumask);
 
-	for_each_cpu(cpu, pd->cpumask) {
-		queue = per_cpu_ptr(pd->queue, cpu);
-		reorder = &queue->reorder;
-
-		/*
-		 * Calculate the seq_nr of the object that should be
-		 * next in this reorder queue.
-		 */
-		overrun = 0;
-		calc_seq_nr = (atomic_read(&queue->num_obj) * num_cpus)
-			       + queue->cpu_index;
-
-		if (unlikely(calc_seq_nr > pd->max_seq_nr)) {
-			calc_seq_nr = calc_seq_nr - pd->max_seq_nr - 1;
-			overrun = 1;
-		}
-
-		if (!list_empty(&reorder->list)) {
-			padata = list_entry(reorder->list.next,
-					    struct padata_priv, list);
-
-			seq_nr  = padata->seq_nr;
-			BUG_ON(calc_seq_nr != seq_nr);
-		} else {
-			seq_nr = calc_seq_nr;
-			empty++;
-		}
-
-		if (next_nr < 0 || seq_nr < next_nr
-		    || (next_overrun && !overrun)) {
-			next_nr = seq_nr;
-			next_overrun = overrun;
-			next_queue = queue;
-		}
+	/*
+	 * Calculate the percpu reorder queue and the sequence
+	 * number of the next object.
+	 */
+	next_nr = pd->processed;
+	next_index = next_nr % num_cpus;
+	cpu = padata_index_to_cpu(pd, next_index);
+	next_queue = per_cpu_ptr(pd->queue, cpu);
+
+	if (unlikely(next_nr > pd->max_seq_nr)) {
+		next_nr = next_nr - pd->max_seq_nr - 1;
+		next_index = next_nr % num_cpus;
+		cpu = padata_index_to_cpu(pd, next_index);
+		next_queue = per_cpu_ptr(pd->queue, cpu);
+		pd->processed = 0;
 	}
 
 	padata = NULL;
 
-	if (empty == num_cpus)
-		goto out;
-
 	reorder = &next_queue->reorder;
 
 	if (!list_empty(&reorder->list)) {
 		padata = list_entry(reorder->list.next,
 				    struct padata_priv, list);
 
-		if (unlikely(next_overrun)) {
-			for_each_cpu(cpu, pd->cpumask) {
-				queue = per_cpu_ptr(pd->queue, cpu);
-				atomic_set(&queue->num_obj, 0);
-			}
-		}
+		BUG_ON(next_nr != padata->seq_nr);
 
 		spin_lock(&reorder->lock);
 		list_del_init(&padata->list);
 		atomic_dec(&pd->reorder_objects);
 		spin_unlock(&reorder->lock);
 
-		atomic_inc(&next_queue->num_obj);
+		pd->processed++;
 
 		goto out;
 	}
@@ -430,7 +398,6 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
 
 		INIT_WORK(&queue->pwork, padata_parallel_worker);
 		INIT_WORK(&queue->swork, padata_serial_worker);
-		atomic_set(&queue->num_obj, 0);
 	}
 
 	num_cpus = cpumask_weight(pd->cpumask);