> Il giorno 03 ott 2018, alle ore 10:28, Linus Walleij <linus.walleij@xxxxxxxxxx> ha scritto: > > On Wed, Oct 3, 2018 at 9:42 AM Damien Le Moal <Damien.LeMoal@xxxxxxx> wrote: > >> There is another class of outliers: host-managed SMR disks (SATA and SCSI, >> definitely single hw queue). For these, using mq-deadline is mandatory in many >> cases in order to guarantee sequential write command delivery to the device >> driver. Having the default changed to bfq, which as far as I know is not SMR >> friendly (can sequential writes within a single zone be reordered ?) is asking >> for troubles (unaligned write errors showing up). > > Ah, that is interesting. > > Which device driver files are we talking about here, specifically? > I'd like to take a look. > > I guess what you say is not that you are looking for the deadline > scheduling per se (as in deadline scheduling is nice), what you want is > the zone locking semantics in that scheduler, is that right? > > I.e. this business: > blk_queue_is_zoned(q) > blk_req_zone_write_lock(rq); > blk_req_zone_write_unlock(rq); > and mq-deadline solves this with a spinlock. > > I will augment the patch to enforce mq-deadline > if blk_queue_is_zoned(q) is true, as it is clear that > any device with that characteristic must use mq-deadline. > > Paoly might be interested in looking into whether BFQ could > also handle zoned devices in the future, I have no idea of how > hard that would be. > Absolutely, as I already wrote in my reply to Damien. In the meantime, Linus, augmenting your patch as you propose seems a clean and effective solution to me. Thanks, Paolo > The zoned business seems a bit fragile. Should it even be > allowed to select any other scheduler than deadline on these > devices? Presenting all compiled in schedulers in > /sysblock/device/queue/scheduler sounds like just giving > sysadmins too much rope. > > Yours, > Linus Walleij
