blk-mq: use __smp_call_function_single directly

__smp_call_function_single already avoids multiple IPIs by internally
queing up the items, and now also is available for non-SMP builds as
a trivially correct stub, so there is no need to wrap it.  If the
additional lock roundtrip cause problems my patch to convert the
generic IPI code to llists is waiting to get merged will fix it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 11 insertions, 57 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 473ce40..68734f8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -27,8 +27,6 @@ static LIST_HEAD(all_q_list);
 
 static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx);
 
-DEFINE_PER_CPU(struct llist_head, ipi_lists);
-
 static struct blk_mq_ctx *__blk_mq_get_ctx(struct request_queue *q,
 					   unsigned int cpu)
 {
@@ -339,55 +337,12 @@ void __blk_mq_end_io(struct request *rq, int error)
 		blk_mq_complete_request(rq, error);
 }
 
-#if defined(CONFIG_SMP)
-
-/*
- * Called with interrupts disabled.
- */
-static void ipi_end_io(void *data)
+static void blk_mq_end_io_remote(void *data)
 {
-	struct llist_head *list = &per_cpu(ipi_lists, smp_processor_id());
-	struct llist_node *entry, *next;
-	struct request *rq;
-
-	entry = llist_del_all(list);
-
-	while (entry) {
-		next = entry->next;
-		rq = llist_entry(entry, struct request, ll_list);
-		__blk_mq_end_io(rq, rq->errors);
-		entry = next;
-	}
-}
-
-static int ipi_remote_cpu(struct blk_mq_ctx *ctx, const int cpu,
-			  struct request *rq, const int error)
-{
-	struct call_single_data *data = &rq->csd;
-
-	rq->errors = error;
-	rq->ll_list.next = NULL;
-
-	/*
-	 * If the list is non-empty, an existing IPI must already
-	 * be "in flight". If that is the case, we need not schedule
-	 * a new one.
-	 */
-	if (llist_add(&rq->ll_list, &per_cpu(ipi_lists, ctx->cpu))) {
-		data->func = ipi_end_io;
-		data->flags = 0;
-		__smp_call_function_single(ctx->cpu, data, 0);
-	}
+	struct request *rq = data;
 
-	return true;
+	__blk_mq_end_io(rq, rq->errors);
 }
-#else /* CONFIG_SMP */
-static int ipi_remote_cpu(struct blk_mq_ctx *ctx, const int cpu,
-			  struct request *rq, const int error)
-{
-	return false;
-}
-#endif
 
 /*
  * End IO on this request on a multiqueue enabled driver. We'll either do
@@ -403,11 +358,15 @@ void blk_mq_end_io(struct request *rq, int error)
 		return __blk_mq_end_io(rq, error);
 
 	cpu = get_cpu();
-
-	if (cpu == ctx->cpu || !cpu_online(ctx->cpu) ||
-	    !ipi_remote_cpu(ctx, cpu, rq, error))
+	if (cpu != ctx->cpu && cpu_online(ctx->cpu)) {
+		rq->errors = error;
+		rq->csd.func = blk_mq_end_io_remote;
+		rq->csd.info = rq;
+		rq->csd.flags = 0;
+		__smp_call_function_single(ctx->cpu, &rq->csd, 0);
+	} else {
 		__blk_mq_end_io(rq, error);
-
+	}
 	put_cpu();
 }
 EXPORT_SYMBOL(blk_mq_end_io);
@@ -1506,11 +1465,6 @@ static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
 
 static int __init blk_mq_init(void)
 {
-	unsigned int i;
-
-	for_each_possible_cpu(i)
-		init_llist_head(&per_cpu(ipi_lists, i));
-
 	blk_mq_cpu_init();
 
 	/* Must be called after percpu_counter_hotcpu_callback() */