#755461 sysstat: iostat shows %util over 600%

Package:
sysstat
Source:
sysstat
Description:
system performance tools for Linux
Submitter:
"hzlaidonglin"
Date:
2014-07-21 05:21:07 UTC
Severity:
important
#755461#5
Date:
2014-07-21 05:13:18 UTC
From:
To:
`iostat -d -xm  2 300` command sometimes reports the device %util more than 600%, here is some sample data:

Device:         rrqm/s   wrqm/s      r/s      w/s    rMB/s    wMB/s avgrq-sz avgqu-sz    await    svctm    %util
sda               0.50  1941.50  1672.50   650.50    21.64    12.89    30.44   992.87   419.89     3.04   706.00
sdb               4.00     0.00  4099.00     4.50    52.54     0.03    26.23   221.54    55.95     1.55   637.60

Device:         rrqm/s   wrqm/s      r/s      w/s    rMB/s    wMB/s avgrq-sz avgqu-sz    await    svctm    %util
sda               0.14    28.47    86.47    12.46     1.09     0.21    27.05    27.92   236.69     1.43    14.16
sdb               0.00     0.57    64.02     0.64     0.93     0.01    29.59     1.10    17.40     2.16    13.97

Device:         rrqm/s   wrqm/s      r/s      w/s    rMB/s    wMB/s avgrq-sz avgqu-sz    await    svctm    %util
sda               0.00   302.50   478.00    63.00     5.96     0.98    26.26   164.55   351.83     1.85   100.00
sdb               0.00     0.00    50.00     3.50     0.44     0.02    17.79     0.41     7.51     4.15    22.20

Device:         rrqm/s   wrqm/s      r/s      w/s    rMB/s    wMB/s avgrq-sz avgqu-sz    await    svctm    %util
sda               1.00  1815.00  2733.50   210.50    31.83     7.85    27.60   712.15   236.17     1.32   390.00
sdb               0.00     6.50  1229.00    14.00    15.07     0.09    24.98    18.21    14.65     2.32   288.00

the value of %util 706.00 and 637.60 is so weird, I know the FAQ of sysstat (http://mcs.une.edu.au/doc/sysstat/FAQ) :

Here is the /proc/diskstats
   8       0 sda 474944638 2793620 25049714746 548686608 176345975 25328578 65025196237 2921137500 0 1442575668 3491692340
   8       1 sda1 2674870 126919 100395082 120325012 245402 327005 7788512 29006272 0 57038148 149376888
   8       2 sda2 9 0 56 188 0 0 0 0 0 172 188
   8       5 sda5 3836864 482461 34554976 28214880 2862978 4521635 59472496 2138232956 0 63530140 2167976168
   8       6 sda6 588700 64237 50975962 84626764 4985183 2429771 106285104 276073212 0 141974932 362510028
   8       7 sda7 121279 9470 1951946 2536004 40667276 15024620 568910584 514104360 0 401159104 517504448
   8       8 sda8 467722599 2110507 24861833980 312981908 127585136 3025547 64282739541 4258687996 0 1359773060 300705596
   8      16 sdb 99373913 93469 2954047151 1172805924 18624102 9319609 3813314137 2412797116 0 263085556 3585802392
   8      17 sdb1 5744817 53811 238884970 30411680 11917662 9194145 605638344 265178520 0 73361380 295592352
   8      18 sdb2 7 0 38 28 0 0 0 0 0 28 28
   8      21 sdb5 93628862 39631 2715160111 1142394088 6706440 125464 3207675793 2147618596 0 197734464 3290269836


But I dont think it's a bug of kernel, because the the value becomes fine after a moment.

Thanks,
Tanglim LUA
07/21/2014