On 03/13/2017 03:25 AM, Adrian Hunter wrote: > On 11/03/17 00:05, Jens Axboe wrote: >> On 03/10/2017 07:21 AM, Adrian Hunter wrote: >>>> Essentially I take out that thread and replace it with this one worker >>>> introduced in this very patch. I agree the driver can block in many ways >>>> and that is why I need to have it running in process context, and this >>>> is what the worker introduced here provides. >>> >>> The last time I looked at the blk-mq I/O scheduler code, it pulled up to >>> qdepth requests from the I/O scheduler and left them on a local list while >>> running ->queue_rq(). That means blocking in ->queue_rq() leaves some >>> number of requests in limbo (not issued but also not in the I/O scheduler) >>> for that time. >> >> Look again, if we're not handling the requeued dispatches, we pull one >> at the time from the scheduler. >> > > That's good :-) > > Now the next thing ;-) > > It looks like we either set BLK_MQ_F_BLOCKING and miss the possibility of > issuing synchronous requests immediately, or we don't set BLK_MQ_F_BLOCKING > in which case we are never allowed to sleep in ->queue_rq(). Is that true? Only one of those statements is true - if you don't set BLK_MQ_F_BLOCKING, then you may never block in your ->queue_rq() function. But if you do set it, it does not preclude immediate issue of sync requests. -- Jens Axboe
