block: describe difference between flags IO_STAT and STATS

This adds reasonable comments, but they definitely needs better names.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index dee46c20701b2c6e8da86a7030096c9445b21f7e..61207560e826ddfa71ef4344d0fe4061490a97cd 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -108,7 +108,7 @@ typedef __u32 __bitwise req_flags_t;
 #define RQF_QUIET              ((__force req_flags_t)(1 << 11))
 /* elevator private data attached */
 #define RQF_ELVPRIV            ((__force req_flags_t)(1 << 12))
-/* account I/O stat */
+/* account into disk and partition IO statistics */
 #define RQF_IO_STAT            ((__force req_flags_t)(1 << 13))
 /* request came from our alloc pool */
 #define RQF_ALLOCED            ((__force req_flags_t)(1 << 14))
@@ -116,7 +116,7 @@ typedef __u32 __bitwise req_flags_t;
 #define RQF_PM                 ((__force req_flags_t)(1 << 15))
 /* on IO scheduler merge hash */
 #define RQF_HASHED             ((__force req_flags_t)(1 << 16))
-/* IO stats tracking on */
+/* track IO completion time */
 #define RQF_STATS              ((__force req_flags_t)(1 << 17))
 /* Look at ->special_vec for the actual data payload instead of the
    bio chain. */
@@ -685,7 +685,7 @@ struct request_queue {
 #define QUEUE_FLAG_FAIL_IO     7       /* fake timeout */
 #define QUEUE_FLAG_NONROT      9       /* non-rotational device (SSD) */
 #define QUEUE_FLAG_VIRT        QUEUE_FLAG_NONROT /* paravirt device */
-#define QUEUE_FLAG_IO_STAT     10      /* do IO stats */
+#define QUEUE_FLAG_IO_STAT     10      /* do disk/partitions IO accounting */
 #define QUEUE_FLAG_DISCARD     11      /* supports DISCARD */
 #define QUEUE_FLAG_NOXMERGES   12      /* No extended merges */
 #define QUEUE_FLAG_ADD_RANDOM  13      /* Contributes to random pool */
@@ -699,7 +699,7 @@ struct request_queue {
 #define QUEUE_FLAG_FUA        21       /* device supports FUA writes */
 #define QUEUE_FLAG_FLUSH_NQ    22      /* flush not queueuable */
 #define QUEUE_FLAG_DAX         23      /* device supports DAX */
-#define QUEUE_FLAG_STATS       24      /* track rq completion times */
+#define QUEUE_FLAG_STATS       24      /* track IO start and completion times */
 #define QUEUE_FLAG_POLL_STATS  25      /* collecting stats for hybrid polling */
 #define QUEUE_FLAG_REGISTERED  26      /* queue has been registered to a disk */
 #define QUEUE_FLAG_SCSI_PASSTHROUGH 27 /* queue supports SCSI commands */