projects / linux-block.git / blame
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|---|---|---|
| 898bd37a | 1 | =============================================== |
| 37a32795 AI |
2 | Block layer statistics in /sys/block/<dev>/stat |
| 3 | =============================================== | |
| 4 | ||
| 5 | This file documents the contents of the /sys/block/<dev>/stat file. | |
| 6 | ||
| 7 | The stat file provides several statistics about the state of block | |
| 8 | device <dev>. | |
| 9 | ||
| 898bd37a MCC |
10 | Q. |
| 11 | Why are there multiple statistics in a single file? Doesn't sysfs | |
| 37a32795 | 12 | normally contain a single value per file? |
| 898bd37a MCC |
13 | |
| 14 | A. | |
| 15 | By having a single file, the kernel can guarantee that the statistics | |
| 37a32795 AI |
16 | represent a consistent snapshot of the state of the device. If the |
| 17 | statistics were exported as multiple files containing one statistic | |
| 18 | each, it would be impossible to guarantee that a set of readings | |
| 19 | represent a single point in time. | |
| 20 | ||
| e53eeac9 | 21 | The stat file consists of a single line of text containing 17 decimal |
| 37a32795 AI |
22 | values separated by whitespace. The fields are summarized in the |
| 23 | following table, and described in more detail below. | |
| 24 | ||
| 898bd37a MCC |
25 | |
| 26 | =============== ============= ================================================= | |
| 37a32795 | 27 | Name units description |
| 898bd37a | 28 | =============== ============= ================================================= |
| 37a32795 AI |
29 | read I/Os requests number of read I/Os processed |
| 30 | read merges requests number of read I/Os merged with in-queue I/O | |
| 31 | read sectors sectors number of sectors read | |
| 32 | read ticks milliseconds total wait time for read requests | |
| 33 | write I/Os requests number of write I/Os processed | |
| 34 | write merges requests number of write I/Os merged with in-queue I/O | |
| 35 | write sectors sectors number of sectors written | |
| 36 | write ticks milliseconds total wait time for write requests | |
| 37 | in_flight requests number of I/Os currently in flight | |
| 38 | io_ticks milliseconds total time this block device has been active | |
| 39 | time_in_queue milliseconds total wait time for all requests | |
| bdca3c87 MC |
40 | discard I/Os requests number of discard I/Os processed |
| 41 | discard merges requests number of discard I/Os merged with in-queue I/O | |
| 42 | discard sectors sectors number of sectors discarded | |
| 43 | discard ticks milliseconds total wait time for discard requests | |
| b6866318 KK |
44 | flush I/Os requests number of flush I/Os processed |
| 45 | flush ticks milliseconds total wait time for flush requests | |
| 898bd37a | 46 | =============== ============= ================================================= |
| 37a32795 | 47 | |
| bdca3c87 MC |
48 | read I/Os, write I/Os, discard I/0s |
| 49 | =================================== | |
| 37a32795 AI |
50 | |
| 51 | These values increment when an I/O request completes. | |
| 52 | ||
| b6866318 KK |
53 | flush I/Os |
| 54 | ========== | |
| 55 | ||
| 56 | These values increment when an flush I/O request completes. | |
| 57 | ||
| 58 | Block layer combines flush requests and executes at most one at a time. | |
| 59 | This counts flush requests executed by disk. Not tracked for partitions. | |
| 60 | ||
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61 | read merges, write merges, discard merges |
| 62 | ========================================= | |
| 37a32795 AI |
63 | |
| 64 | These values increment when an I/O request is merged with an | |
| 65 | already-queued I/O request. | |
| 66 | ||
| bdca3c87 MC |
67 | read sectors, write sectors, discard_sectors |
| 68 | ============================================ | |
| 37a32795 | 69 | |
| bdca3c87 MC |
70 | These values count the number of sectors read from, written to, or |
| 71 | discarded from this block device. The "sectors" in question are the | |
| 72 | standard UNIX 512-byte sectors, not any device- or filesystem-specific | |
| 73 | block size. The counters are incremented when the I/O completes. | |
| 37a32795 | 74 | |
| b6866318 KK |
75 | read ticks, write ticks, discard ticks, flush ticks |
| 76 | =================================================== | |
| 37a32795 AI |
77 | |
| 78 | These values count the number of milliseconds that I/O requests have | |
| 79 | waited on this block device. If there are multiple I/O requests waiting, | |
| 80 | these values will increase at a rate greater than 1000/second; for | |
| 81 | example, if 60 read requests wait for an average of 30 ms, the read_ticks | |
| 82 | field will increase by 60*30 = 1800. | |
| 83 | ||
| 84 | in_flight | |
| 85 | ========= | |
| 86 | ||
| 87 | This value counts the number of I/O requests that have been issued to | |
| 88 | the device driver but have not yet completed. It does not include I/O | |
| 89 | requests that are in the queue but not yet issued to the device driver. | |
| 90 | ||
| 91 | io_ticks | |
| 92 | ======== | |
| 93 | ||
| 94 | This value counts the number of milliseconds during which the device has | |
| 95 | had I/O requests queued. | |
| 96 | ||
| 97 | time_in_queue | |
| 98 | ============= | |
| 99 | ||
| 100 | This value counts the number of milliseconds that I/O requests have waited | |
| 101 | on this block device. If there are multiple I/O requests waiting, this | |
| 102 | value will increase as the product of the number of milliseconds times the | |
| 103 | number of requests waiting (see "read ticks" above for an example). |