On 4/4/23 20:24, Niklas Cassel wrote:
From: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx> IO priorities currently only use 6-bits of the 16-bits ioprio value: the 3-upper bits are used to define up to 8 priority classes (4 of which are valid) and the 3 lower bits of the value are used to define a priority level for the real-time and best-effort class. The remaining 10-bits between the IO priority class and level are unused, and in fact, cannot be used by the user as doing so would either result in the value being completely ignored, or in an error returned by ioprio_check_cap(). Use these 10-bits of an ioprio value to allow a user to specify IO hints. An IO hint is defined as a 10-bits value, allowing up to 1023 different hints to be specified, with the value 0 being reserved as the "no hint" case. An IO hint can apply to any IO that specifies a valid priority class other than NONE, regardless of the IO priority level specified. To do so, the macros IOPRIO_PRIO_HINT() and IOPRIO_PRIO_VALUE_HINT() are introduced in include/uapi/linux/ioprio.h to respectively allow a user to get and set a hint in an ioprio value. To support the ATA and SCSI command duration limits feature, 7 hints are defined: IOPRIO_HINT_DEV_DURATION_LIMIT_1 to IOPRIO_HINT_DEV_DURATION_LIMIT_7, allowing a user to specify which command duration limit descriptor should be applied to the commands serving an IO. Specifying these hints has for now no effect whatsoever if the target block devices do not support the command duration limits feature. However, in the future, block IO schedulers can be modified to optimize IO issuing order based on these hints, even for devices that do not support the command duration limits feature. Given that the 7 duration limits hints defined have no effect on any block layer component, the actual definition of the duration limits implied by these hints remains at the device level. Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx> Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxx> --- include/uapi/linux/ioprio.h | 49 +++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+)
Reviewed-by: Hannes Reinecke <hare@xxxxxxx> Cheers, Hannes
