[Xen-users] xenstat_domain_cpu_ns() occasionally returns a huge value

[Andy Smith <andy@xxxxxxxxxxxxxx>]

Hi,

I was writing a little utility to dump out domain CPU times and I
noticed that occasionally xenstat_domain_cpu_ns() returns an
erroneous huge value like 9223488034477457013.

Attached is a small test program that just requests every domain's
CPU time in a tight loop; it received such a result after less than
3 minutes running in dom0 of a host with only dom0 and two other PV
domains running:

$ make cpu_time_test
cc -Wall  -lxenstat -lyajl -Wl,-rpath,/usr/lib/xen-4.12/lib 
-L/usr/lib/xen-4.12/lib  cpu_time_test.c   -o cpu_time_test
$ sudo time ./cpu_time_test
Got a weird CPU time 9223488108.867305 >100 years (cpu_ns=9223488108867304818)
Command exited with non-zero status 1
84.07user 41.90system 2:40.20elapsed 78%CPU (0avgtext+0avgdata 
39780maxresident)k
0inputs+0outputs (0major+9541minor)pagefaults 0swaps

The erroneous results are always somewhere above 922xxxxxxxxxxxxxxxx
nanoseconds (some 285 years of CPU time if it were genuine!). Then
the next reading will be normal. Very occasionally I've seen two in
a row. I see this on both 4.12 and 4.10.

My C is very rusty so I've probably made a simple error and don't
want to bother xen-devel with it; can someone familiar with using
the xenstat interface please tell me what I've done wrong here?

Thanks,
Andy

Attachment: cpu_time_test.c
Description: Text Data

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