On 13/03/17 16:19, Jens Axboe wrote: > 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. I meant it gets put to the workqueue rather than issued in the context of the submitter.
