diff options
author | Russell King <rmk@dyn-67.arm.linux.org.uk> | 2006-01-09 14:18:33 -0500 |
---|---|---|
committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2006-01-09 14:18:33 -0500 |
commit | 0a3a98f6dd4e8f4d928a09302c0d1c56f2192ac3 (patch) | |
tree | 92f55e374a84d06ce8213a4540454760fdecf137 /Documentation/block/stat.txt | |
parent | 8ef12c9f01afba47c2d33bb939085111ca0d0f7d (diff) | |
parent | 5367f2d67c7d0bf1faae90e6e7b4e2ac3c9b5e0f (diff) |
Merge Linus' tree.
Diffstat (limited to 'Documentation/block/stat.txt')
-rw-r--r-- | Documentation/block/stat.txt | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/Documentation/block/stat.txt b/Documentation/block/stat.txt new file mode 100644 index 000000000000..0dbc946de2ea --- /dev/null +++ b/Documentation/block/stat.txt | |||
@@ -0,0 +1,82 @@ | |||
1 | Block layer statistics in /sys/block/<dev>/stat | ||
2 | =============================================== | ||
3 | |||
4 | This file documents the contents of the /sys/block/<dev>/stat file. | ||
5 | |||
6 | The stat file provides several statistics about the state of block | ||
7 | device <dev>. | ||
8 | |||
9 | Q. Why are there multiple statistics in a single file? Doesn't sysfs | ||
10 | normally contain a single value per file? | ||
11 | A. By having a single file, the kernel can guarantee that the statistics | ||
12 | represent a consistent snapshot of the state of the device. If the | ||
13 | statistics were exported as multiple files containing one statistic | ||
14 | each, it would be impossible to guarantee that a set of readings | ||
15 | represent a single point in time. | ||
16 | |||
17 | The stat file consists of a single line of text containing 11 decimal | ||
18 | values separated by whitespace. The fields are summarized in the | ||
19 | following table, and described in more detail below. | ||
20 | |||
21 | Name units description | ||
22 | ---- ----- ----------- | ||
23 | read I/Os requests number of read I/Os processed | ||
24 | read merges requests number of read I/Os merged with in-queue I/O | ||
25 | read sectors sectors number of sectors read | ||
26 | read ticks milliseconds total wait time for read requests | ||
27 | write I/Os requests number of write I/Os processed | ||
28 | write merges requests number of write I/Os merged with in-queue I/O | ||
29 | write sectors sectors number of sectors written | ||
30 | write ticks milliseconds total wait time for write requests | ||
31 | in_flight requests number of I/Os currently in flight | ||
32 | io_ticks milliseconds total time this block device has been active | ||
33 | time_in_queue milliseconds total wait time for all requests | ||
34 | |||
35 | read I/Os, write I/Os | ||
36 | ===================== | ||
37 | |||
38 | These values increment when an I/O request completes. | ||
39 | |||
40 | read merges, write merges | ||
41 | ========================= | ||
42 | |||
43 | These values increment when an I/O request is merged with an | ||
44 | already-queued I/O request. | ||
45 | |||
46 | read sectors, write sectors | ||
47 | =========================== | ||
48 | |||
49 | These values count the number of sectors read from or written to this | ||
50 | block device. The "sectors" in question are the standard UNIX 512-byte | ||
51 | sectors, not any device- or filesystem-specific block size. The | ||
52 | counters are incremented when the I/O completes. | ||
53 | |||
54 | read ticks, write ticks | ||
55 | ======================= | ||
56 | |||
57 | These values count the number of milliseconds that I/O requests have | ||
58 | waited on this block device. If there are multiple I/O requests waiting, | ||
59 | these values will increase at a rate greater than 1000/second; for | ||
60 | example, if 60 read requests wait for an average of 30 ms, the read_ticks | ||
61 | field will increase by 60*30 = 1800. | ||
62 | |||
63 | in_flight | ||
64 | ========= | ||
65 | |||
66 | This value counts the number of I/O requests that have been issued to | ||
67 | the device driver but have not yet completed. It does not include I/O | ||
68 | requests that are in the queue but not yet issued to the device driver. | ||
69 | |||
70 | io_ticks | ||
71 | ======== | ||
72 | |||
73 | This value counts the number of milliseconds during which the device has | ||
74 | had I/O requests queued. | ||
75 | |||
76 | time_in_queue | ||
77 | ============= | ||
78 | |||
79 | This value counts the number of milliseconds that I/O requests have waited | ||
80 | on this block device. If there are multiple I/O requests waiting, this | ||
81 | value will increase as the product of the number of milliseconds times the | ||
82 | number of requests waiting (see "read ticks" above for an example). | ||