blk-mq: reduce unnecessary software queue looping
In flush_busy_ctxs() and blk_mq_hctx_has_pending(), regardless of how many
ctxs assigned to one hctx, they will all loop hctx->ctx_map.map_size
times. Here hctx->ctx_map.map_size is a const ALIGN(nr_cpu_ids, 8) / 8.
Especially, flush_busy_ctxs() is in hot code path. And it's unnecessary.
Change ->map_size to contain the actually mapped software queues, so we
only loop for as many iterations as we have to.
And remove cpumask setting and nr_ctx count in blk_mq_init_cpu_queues()
since they are all re-done in blk_mq_map_swqueue().
blk_mq_map_swqueue().
Signed-off-by: Chong Yuan <chong.yuan@memblaze.com>
Reviewed-by: Wenbo Wang <wenbo.wang@memblaze.com>
Updated by me for formatting and commenting.
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 1192f85..0b49e42 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1522,8 +1522,6 @@
if (!bitmap->map)
return -ENOMEM;
- bitmap->map_size = num_maps;
-
total = nr_cpu_ids;
for (i = 0; i < num_maps; i++) {
bitmap->map[i].depth = min(total, bitmap->bits_per_word);
@@ -1764,8 +1762,6 @@
continue;
hctx = q->mq_ops->map_queue(q, i);
- cpumask_set_cpu(i, hctx->cpumask);
- hctx->nr_ctx++;
/*
* Set local node, IFF we have more than one hw queue. If
@@ -1802,6 +1798,8 @@
}
queue_for_each_hw_ctx(q, hctx, i) {
+ struct blk_mq_ctxmap *map = &hctx->ctx_map;
+
/*
* If no software queues are mapped to this hardware queue,
* disable it and free the request entries.
@@ -1818,6 +1816,13 @@
}
/*
+ * Set the map size to the number of mapped software queues.
+ * This is more accurate and more efficient than looping
+ * over all possibly mapped software queues.
+ */
+ map->map_size = hctx->nr_ctx / map->bits_per_word;
+
+ /*
* Initialize batch roundrobin counts
*/
hctx->next_cpu = cpumask_first(hctx->cpumask);