The I/O priority user interface defines the 16-bits ioprio values as the combination of the upper 3-bits for an I/O priority class and the lower 13-bits as priority data. However, the kernel only uses the lower 3-bits of the priority data to define priority levels for the RT and BE priority classes. The data part of an ioprio value is completely ignored for the IDLE and NONE classes. This is enforced by checks done in ioprio_check_cap(), which is called for all paths that allow defining an I/O priority for I/Os: the per-context ioprio_set() system call, aio interface and io_uring interface. Clarify this fact in the uapi ioprio.h header file and introduce the IOPRIO_PRIO_LEVEL_MASK and IOPRIO_PRIO_LEVEL() macros for users to define and get priority levels in an ioprio value. The coarser macro IOPRIO_PRIO_DATA() is retained for backward compatibility with old applications already using it. There is no functional change introduced with this. In-kernel users of the IOPRIO_PRIO_DATA() macro which are explicitly handling I/O priority data as a priority level are modified to use the new IOPRIO_PRIO_LEVEL() macro without any functional change. Since f2fs is the only user of this macro not explicitly using that value as a priority level, it is left unchanged.
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| @@ -17,7 +17,7 @@ · 16 unmodified lines | ||
| 17 | 17 | ((data) & IOPRIO_PRIO_MASK)) |
| 18 | 18 | |
| 19 | 19 | /* |
| 20 | − * These are the io priority groups as implemented by the BFQ and mq-deadline | |
| 20 | + * These are the io priority classes as implemented by the BFQ and mq-deadline | |
| 21 | 21 | * schedulers. RT is the realtime class, it always gets premium service. For |
| 22 | 22 | * ATA disks supporting NCQ IO priority, RT class IOs will be processed using |
| 23 | 23 | * high priority NCQ commands. BE is the best-effort scheduling class, the |
| @@ -32,11 +32,20 @@ enum { · 8 unmodified lines | ||
| 32 | 32 | }; |
| 33 | 33 | |
| 34 | 34 | /* |
| 35 | − * The RT and BE priority classes both support up to 8 priority levels. | |
| 35 | + * The RT and BE priority classes both support up to 8 priority levels that | |
| 36 | + * can be specified using the lower 3-bits of the priority data. | |
| 36 | 37 | */ |
| 37 | −#define IOPRIO_NR_LEVELS 8 | |
| 38 | −#define IOPRIO_BE_NR IOPRIO_NR_LEVELS | |
| 38 | +#define IOPRIO_LEVEL_NR_BITS 3 | |
| 39 | +#define IOPRIO_NR_LEVELS (1 << IOPRIO_LEVEL_NR_BITS) | |
| 40 | +#define IOPRIO_LEVEL_MASK (IOPRIO_NR_LEVELS - 1) | |
| 41 | +#define IOPRIO_PRIO_LEVEL(ioprio) ((ioprio) & IOPRIO_LEVEL_MASK) | |
| 39 | 42 | |
| 43 | +#define IOPRIO_BE_NR IOPRIO_NR_LEVELS | |
| 44 | + | |
| 45 | +/* | |
| 46 | + * Possible values for the "which" argument of the ioprio_get() and | |
| 47 | + * ioprio_set() system calls (see "man ioprio_set"). | |
| 48 | + */ | |
| 40 | 49 | enum { |
| 41 | 50 | IOPRIO_WHO_PROCESS = 1, |
| 42 | 51 | IOPRIO_WHO_PGRP, |
| @@ -44,7 +53,7 @@ enum { · 1 unmodified line | ||
| 44 | 53 | }; |
| 45 | 54 | |
| 46 | 55 | /* |
| 47 | − * Fallback BE priority level. | |
| 56 | + * Fallback BE class priority level. | |
| 48 | 57 | */ |
| 49 | 58 | #define IOPRIO_NORM 4 |
| 50 | 59 | #define IOPRIO_BE_NORM IOPRIO_NORM |