On Tue, Apr 02, 2019 at 08:44:10AM -0700, Bart Van Assche wrote:
On Tue, 2019-04-02 at 08:53 +0800, Ming Lei wrote:
On Mon, Apr 01, 2019 at 02:20:12PM -0700, Bart Van Assche wrote:
diff --git a/block/blk-mq.c b/block/blk-mq.c index 3ff3d7b49969..652d0c6d5945 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1499,12 +1499,20 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async) struct blk_mq_hw_ctx *hctx; int i;
- /*
* Do not run any hardware queues if the queue is frozen or if a* concurrent blk_cleanup_queue() call is removing any data* structures used by this function.*/- if (!percpu_ref_tryget(&q->q_usage_counter))
return;blk_mq_run_hw_queue(hctx, async); }
- percpu_ref_put(&q->q_usage_counter);
} EXPORT_SYMBOL(blk_mq_run_hw_queues);
I don't see it is necessary to add percpu_ref_tryget()/percpu_ref_put() in the fast path if we simply release all hctx resource in hctx's release handler by the following patch:
https://lore.kernel.org/linux-block/20190401044247.29881-2-ming.lei@redhat.c...
Even we can kill the percpu_ref_tryget_live()/percpu_ref_put() in scsi_end_request().
The above approach has the advantages of being easy to review and to maintain.
Patch "[PATCH V2 1/3] blk-mq: free hw queue's resource in hctx's release handler" makes the block layer more complicated because it introduces a new state for hardware queues: block driver cleanup has happened (set->ops->exit_hctx(...)) but
We are done with driver after blk_freeze_queue() and blk_sync_queue(), then call .exit_hctx() to say good bye with driver, I don't see it causes any issue.
the hardware queues are still in use by the block layer core.
Block layer has the correct in-memory state to work well, and no driver activity is involved too.
Thanks, Ming