On Tue, Feb 05, 2019 at 03:09:28PM +0000, John Garry wrote: > On 05/02/2019 14:52, Keith Busch wrote: > > On Tue, Feb 05, 2019 at 05:24:11AM -0800, John Garry wrote: > > > On 04/02/2019 07:12, Hannes Reinecke wrote: > > > > > > Hi Hannes, > > > > > > > > > > > So, as the user then has to wait for the system to declars 'ready for > > > > CPU remove', why can't we just disable the SQ and wait for all I/O to > > > > complete? > > > > We can make it more fine-grained by just waiting on all outstanding I/O > > > > on that SQ to complete, but waiting for all I/O should be good as an > > > > initial try. > > > > With that we wouldn't need to fiddle with driver internals, and could > > > > make it pretty generic. > > > > > > I don't fully understand this idea - specifically, at which layer would > > > we be waiting for all the IO to complete? > > > > Whichever layer dispatched the IO to a CPU specific context should > > be the one to wait for its completion. That should be blk-mq for most > > block drivers. > > For SCSI devices, unfortunately not all IO sent to the HW originates from > blk-mq or any other single entity. Then they'll need to register their own CPU notifiers and handle the ones they dispatched.
