| Message ID | 20230404182428.715140-3-nks@flawful.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add Command Duration Limits support | expand |
On 4/4/23 20:24, Niklas Cassel wrote: > From: Damien Le Moal <damien.lemoal@opensource.wdc.com> > > 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@opensource.wdc.com> > Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com> > --- > include/uapi/linux/ioprio.h | 49 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 49 insertions(+) > Reviewed-by: Hannes Reinecke <hare@suse.de> Cheers, Hannes
diff --git a/include/uapi/linux/ioprio.h b/include/uapi/linux/ioprio.h index 4444b4e4fdad..607c7617b9d2 100644 --- a/include/uapi/linux/ioprio.h +++ b/include/uapi/linux/ioprio.h @@ -58,4 +58,53 @@ enum { #define IOPRIO_NORM 4 #define IOPRIO_BE_NORM IOPRIO_NORM +/* + * The 10-bits between the priority class and the priority level are used to + * optionally define IO hints for any combination of IO priority class and + * level. Depending on the kernel configuration, IO scheduler being used and + * the target IO device being used, hints can influence how IOs are processed + * without affecting the IO scheduling ordering defined by the IO priority + * class and level. + */ +#define IOPRIO_HINT_SHIFT IOPRIO_LEVEL_NR_BITS +#define IOPRIO_HINT_NR_BITS 10 +#define IOPRIO_NR_HINTS (1 << IOPRIO_HINT_NR_BITS) +#define IOPRIO_HINT_MASK (IOPRIO_NR_HINTS - 1) +#define IOPRIO_PRIO_HINT(ioprio) \ + (((ioprio) >> IOPRIO_HINT_SHIFT) & IOPRIO_HINT_MASK) + +/* + * Alternate macro for IOPRIO_PRIO_VALUE() to define an IO priority with + * a class, level and hint. + */ +#define IOPRIO_PRIO_VALUE_HINT(class, level, hint) \ + ((((class) & IOPRIO_CLASS_MASK) << IOPRIO_CLASS_SHIFT) | \ + (((hint) & IOPRIO_HINT_MASK) << IOPRIO_HINT_SHIFT) | \ + ((level) & IOPRIO_LEVEL_MASK)) + +/* + * IO hints. + */ +enum { + /* No hint */ + IOPRIO_HINT_NONE = 0, + + /* + * Device command duration limits: indicate to the device a desired + * duration limit for the commands that will be used to process an IO. + * These will currently only be effective for SCSI and ATA devices that + * support the command duration limits feature. If this feature is + * enabled, then the commands issued to the device to process an IO with + * one of these hints set will have the duration limit index (dld field) + * set to the value of the hint. + */ + IOPRIO_HINT_DEV_DURATION_LIMIT_1 = 1, + IOPRIO_HINT_DEV_DURATION_LIMIT_2 = 2, + IOPRIO_HINT_DEV_DURATION_LIMIT_3 = 3, + IOPRIO_HINT_DEV_DURATION_LIMIT_4 = 4, + IOPRIO_HINT_DEV_DURATION_LIMIT_5 = 5, + IOPRIO_HINT_DEV_DURATION_LIMIT_6 = 6, + IOPRIO_HINT_DEV_DURATION_LIMIT_7 = 7, +}; + #endif /* _UAPI_LINUX_IOPRIO_H */