On Fri, Dec 21, 2018 at 12:22:33PM -0700, Jens Axboe wrote: > If an application sets IOCTX_FLAG_SCQTHREAD, the io_context gets a > single thread backing. If used with buffered IO, this will limit > the device queue depth to 1, but it will be async, IOs will simply > be serialized. > > Or an application can set IOCTX_FLAG_SQWQ, in which case the io_context > gets a work queue backing. The concurrency level is the mininum of > twice the available CPUs, or the queue depth specific for the context. > For this mode, we attempt to do buffered reads inline, in case they are > cached. So we should only punt to a workqueue, if we would have to block > to get our data. I'm really worried about having this code present twice. Do we have strong use cases for both? Can't we emulate IOCTX_FLAG_SCQTHREAD good enough with a workqueue without concurrency management?
