Jens Axboe <ax...@kernel.dk> writes:
> On 10/22/2015 09:53 AM, Jeff Moyer wrote:
>> I think that percolating BLK_MQ_F_TAG_SHARED up to the tag set would
>> allow newly created hctxs to simply inherit the shared state (in
>> blk_mq_init_hctx), and you won't need to freeze every queue in order to
>> guarantee that.
>>
>> I was writing a patch to that effect. I've now stopped as I want to
>> make sure I'm not off in the weeds. :)
>
> If that is where the delay is done, then yes, that should fix it and
> be a trivial patch.
It's not quite as trivial as I had hoped. Jason, can you give the
attached patch a try? All I've done is boot tested it so far.
Thanks!
Jeff
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7785ae9..8b4c484 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1860,27 +1860,26 @@ static void blk_mq_map_swqueue(struct request_queue *q,
}
}
-static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)
+static void queue_set_hctx_shared(struct request_queue *q, bool shared)
{
struct blk_mq_hw_ctx *hctx;
- struct request_queue *q;
- bool shared;
int i;
- if (set->tag_list.next == set->tag_list.prev)
- shared = false;
- else
- shared = true;
+ queue_for_each_hw_ctx(q, hctx, i) {
+ if (shared)
+ hctx->flags |= BLK_MQ_F_TAG_SHARED;
+ else
+ hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
+ }
+}
+
+static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, bool
shared)
+{
+ struct request_queue *q;
list_for_each_entry(q, &set->tag_list, tag_set_list) {
blk_mq_freeze_queue(q);
-
- queue_for_each_hw_ctx(q, hctx, i) {
- if (shared)
- hctx->flags |= BLK_MQ_F_TAG_SHARED;
- else
- hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
- }
+ queue_set_hctx_shared(q, shared);
blk_mq_unfreeze_queue(q);
}
}
@@ -1891,7 +1890,13 @@ static void blk_mq_del_queue_tag_set(struct
request_queue *q)
mutex_lock(&set->tag_list_lock);
list_del_init(&q->tag_set_list);
- blk_mq_update_tag_set_depth(set);
+
+ if (set->tag_list.next == set->tag_list.prev) {
+ /* just transitioned to unshared */
+ set->flags &= ~BLK_MQ_F_TAG_SHARED;
+ /* update existing queue */
+ blk_mq_update_tag_set_depth(set, false);
+ }
mutex_unlock(&set->tag_list_lock);
}
@@ -1902,7 +1907,24 @@ static void blk_mq_add_queue_tag_set(struct
blk_mq_tag_set *set,
mutex_lock(&set->tag_list_lock);
list_add_tail(&q->tag_set_list, &set->tag_list);
- blk_mq_update_tag_set_depth(set);
+
+ if (set->tag_list.next != set->tag_list.prev) {
+ /*
+ * Only update the tag set state if the state has
+ * actually changed.
+ */
+ if (!(set->flags & BLK_MQ_F_TAG_SHARED)) {
+ /* just transitioned to shared tags */
+ set->flags |= BLK_MQ_F_TAG_SHARED;
+ blk_mq_update_tag_set_depth(set, true);
+ } else {
+ /* ensure we didn't race with another addition */
+ struct blk_mq_hw_ctx *hctx = queue_first_hw_ctx(q);
+ if ((hctx->flags & BLK_MQ_F_TAG_SHARED) !=
+ BLK_MQ_F_TAG_SHARED)
+ queue_set_hctx_shared(q, true);
+ }
+ }
mutex_unlock(&set->tag_list_lock);
}
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 5e7d43a..12ffc40 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -254,6 +254,9 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
for ((i) = 0; (i) < (hctx)->nr_ctx && \
({ ctx = (hctx)->ctxs[(i)]; 1; }); (i)++)
+#define queue_first_hw_ctx(q) \
+ (q)->queue_hw_ctx[0]
+
#define blk_ctx_sum(q, sum) \
({ \
struct blk_mq_ctx *__x; \
--
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