On Tue, Jan 23, 2018 at 10:01:37PM +0000, Bart Van Assche wrote: > On Wed, 2018-01-24 at 00:59 +0800, Ming Lei wrote: > > How is that enough to fix the IO hang when driver returns STS_RESOURCE > > and the queue is idle? If you want to follow previous dm-rq's way of > > call blk_mq_delay_run_hw_queue() in .queue_rq(), the same trick need > > to be applied to other drivers too, right? > > > > Unfortunately most of STS_RESOURCE don't use this trick, but they need > > to be handled. > > > > The patch of 'blk-mq: introduce BLK_STS_DEV_RESOURCE' can fix all these > > cases. > > The goal of my proposal was to address the race between running the queue and > adding requests back to the dispatch queue only. Regarding the I/O hangs that > can occur if a block driver returns BLK_STS_RESOURCE: since all of these can > be addressed by inserting blk_mq_delay_run_hw_queue() calls in the affected > block drivers I prefer to modify the block drivers instead of making the > blk-mq core even more complicated. IMO, this change doesn't make blk-mq code more complicated, also it is well documented, see the change in block layer: block/blk-core.c | 1 + block/blk-mq.c | 19 +++++++++++++++---- include/linux/blk_types.h | 18 ++++++++++++++++++ Also 21 lines of them are comment, so only 17 lines code change needed in block layer. If inserting blk_mq_delay_run_hw_queue() to driver, the change can be a bit complicated, since call_rcu has to be used, you need to figure out one way to provide callback and the parameter. Even you have to document the change in each driver. [ming@ming linux]$ git grep -n BLK_STS_RESOURCE drivers/ | wc -l 42 There are at least 42 uses of BLK_STS_RESOURCE in drivers, in theory you should insert call_rcu(blk_mq_delay_run_hw_queue) in every BLK_STS_RESOURCE of drivers. I leave the decisions to Jens and drivers maintainers. Thanks, Ming
