Before I create an issue, I'd like to know if anyone else can reproduce
this on an active server?
The following kstat/awk script reports kstat anomalies where
[rw](len)time fields inside a kstat_io[1] structure actually *decrease*
in value:
kstat -c disk -p sd:::*time 1 |
nawk '/time/ {
if (old[$1] && old[$1] > $2)
print $1,"old: "old[$1],"new:"$2
old[$1]=$2
}'
sd:39:sd39:rlentime old: 7223147599853 new:7223146752623
sd:39:sd39:rtime old: 1556295270928 new:1556295116623
sd:21:sd21:rlentime old: 44879798465601 new:44879798422271
sd:24:sd24:wlentime old: 15995502763 new:15995464571
sd:24:sd24:wtime old: 15595171901 new:15595120298
sd:38:sd38:wlentime old: 16762450959 new:16762280835
sd:38:sd38:wtime old: 16293043067 new:16292872942
sd:15:sd15:wlentime old: 16274495238 new:16274415688
sd:15:sd15:wtime old: 15857746407 new:15857664000
sd:2:sd2:wlentime old: 16300070951 new:16299959181
sd:2:sd2:wtime old: 15882033262 new:15881917149
sd:31:sd31:rlentime old: 7260803325344 new:7260802679629
sd:31:sd31:rtime old: 1558548730649 new:1558548606359
Here's the story behind this:
Several times now I've seen iostat -xn <interval> report broken values
for the wait, wsvc_t and %w columns.
The outrageously large values led me to believe we're dealing with
a 64bit signed/unsigned overflow.
Looking at the code and the definitions in kstat.h, these columns are
derived from data in the kstat_io structure.
According to the description of the structure, all fields in there
should increase monotonously.
I also have examples for the old perl-based kstat; I wanted to make
sure I wasn't seeing any artefact of the conversion to floating point.
Anyone else seeing this?
Is this a case of improper reporting (inappropriate caching) or
improper recording in the kernel (missing locks)?
Cheers,
Henk Langeveld
[1]http://src.illumos.org/source/s?defs=kstat_io&project=illumos-gate
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