On Mon, Dec 17, 2018 at 11:42:28AM -0800, Liu Bo wrote: > On Mon, Dec 17, 2018 at 8:04 AM Dennis Zhou <dennis@xxxxxxxxxx> wrote: > > > > The blk-iolatency controller measures the time from rq_qos_throttle() to > > rq_qos_done_bio() and attributes this time to the first bio that needs > > to create the request. This means if a bio is plug-mergeable or > > bio-mergeable, it gets to bypass the blk-iolatency controller. > > > > Hi, > > I have a question about merging in plug list, since plug merges are > done before rq_qos_throttle(), why would plug-mergeable bios bypass > the controller? > > thanks, > liubo > Hi Liubo, BIO_TRACKED is tagging the bio that is responsible for allocating a new request, so that rq_qos controllers can decide whether or not they want to process the bio any part of the way. I should have phrased that a little better in the commit message. It's not that the bio itself is bypassing the blk-iolatency controller, but the blk-iolatency controller deciding to not do anything based on the BIO_TRACKED flag. This doesn't change any of the function calls made on a bio/request. Thanks, Dennis
