On Wed, Nov 10, 2021 at 11:22:05AM +0100, Hannes Reinecke wrote: > On 11/10/21 10:14 AM, Christoph Hellwig wrote: > > Hi Jens and Ming, > > > > I've been looking into properly supporting queue freezing for bio based > > drivers (that is only release q_usage_counter on bio completion for them). > > And the deeper I look into the code the more I'm confused by us having > > the blk_mq_quiesce* interface in addition to blk_freeze_queue. What > > is a good reason to do a quiesce separately from a freeze? > > > IIRC the 'quiesce' interface was an abstraction from the SCSI 'quiesce' > operation, where we had to stop all I/O except for TMFs and scanning. > And 'freeze' was designed fro stopping all I/O. > > But I'm not sure if that ever was the distinction, or if it still > applies today. > > And yeah, I've been wondering myself. > > Probably we should just kill the 'quiesce' stuff and see where we end up :-) In case of EH, no queued requests can be completed, however driver still needs to stop queue and reset hardware, then how can you use freeze to stop queue? See nvme_dev_disable(). Freeze can stop to allocate new request and drain all queued requests, but it can't prevent IO from being queued to LLD. On the contrary, blk_mq_freeze_queue_wait() requires LLD to handle IO for moving on, otherwise it will wait forever. Thanks, Ming
