On Fri, Mar 10, 2017 at 9:29 AM, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > On 10/03/17 00:39, Linus Walleij wrote: >> On Fri, Mar 3, 2017 at 1:22 PM, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >>> On 15/02/17 15:49, Linus Walleij wrote: >>>> On Fri, Feb 10, 2017 at 1:55 PM, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >>>> >>>>> Enhance mmc_blk_data_prep() to support CQE requests. >>>>> >>>>> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx> >>>> >>>> Hey: >>>> >>>>> +#include <linux/ioprio.h> >>>> (...) >>>>> + if (IOPRIO_PRIO_CLASS(req_get_ioprio(req)) == IOPRIO_CLASS_RT) >>>>> + brq->data.flags |= MMC_DATA_PRIO; >>>> >>>> What is this? >>> >>> It is the command queue priority. >>> >>> The command queue supports 2 priorities: "high" (1) and "simple" (0). The >>> eMMC will give "high" priority tasks priority over "simple" priority tasks. >>> >>> So here we give priority to IOPRIO_CLASS_RT which seems appropriate. >> >> So if I understand correctly, you are obtaining the block layer scheduling >> priorities, that can (only?) be set by ionice has from the command line? > > AFAICS it is the ioprio_set() system call . OK to be clear, correct, it is set by that system call. And as far as I can tell there is exactly one program in the world that issues that syscall, and that is ionice(1). It is described to the world as a way for users to give hints to the I/O scheduler about how to manage requests. For example a user can hint that some IO is a backup job and not important and some IO is a media player and really important. And since the block layer only handles this hint in the legacy blk CFQ scheduler I want to know from the block layer developers if this priority has any future. BFQ does not use this hint at all, I think Paolo described the ionice command as problematic, and we need to understand if user-provided IO scheduling hints is something that is going to be used in the future. Yours, Linus Walleij
