1 The following is a demonstration of the iopending tool,
3 Here we run it with a sample interval of 1 second,
6 Tracing... Please wait.
7 2006 Jan 6 20:21:59, load: 0.02, disk_r: 0 KB, disk_w: 0 KB
9 value ------------- Distribution ------------- count
11 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1010
14 2006 Jan 6 20:22:00, load: 0.03, disk_r: 0 KB, disk_w: 0 KB
16 value ------------- Distribution ------------- count
18 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1000
21 2006 Jan 6 20:22:01, load: 0.03, disk_r: 0 KB, disk_w: 0 KB
23 value ------------- Distribution ------------- count
25 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1000
30 The iopending tool samples at 1000 Hz, and prints a distribution of how many
31 disk events were "pending" completion. In the above example the disks are
32 quiet - for all the samples there are zero disk events pending.
36 Now iopending is run with no arguments. It will default to an interval of 5
40 Tracing... Please wait.
41 2006 Jan 6 19:15:41, load: 0.03, disk_r: 3599 KB, disk_w: 0 KB
43 value ------------- Distribution ------------- count
45 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 4450
55 In the above output there was a little disk activity. For 390 samples there
56 was 1 I/O event pending; for 80 samples there was 2, and so on.
61 In the following example iopending is run during heavy disk activity. We
62 print output every 10 seconds,
65 Tracing... Please wait.
66 2006 Jan 6 20:58:07, load: 0.03, disk_r: 25172 KB, disk_w: 33321 KB
68 value ------------- Distribution ------------- count
71 1 |@@@@@@@@@@@@@@@@@@@@@@@@@@@ 6720
81 2006 Jan 6 20:58:17, load: 0.05, disk_r: 8409 KB, disk_w: 12449 KB
83 value ------------- Distribution ------------- count
85 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 7260
121 In the first output, most of the time (67%) there was 1 event pending,
122 and for a short time there were 8 events pending. In the second output we
123 see many samples were off the scale - 650 samples at 32 or more pending
124 events. For this sample I had typed "sync" in another window, which
125 queued many disk events immediately which were eventually completed.