14131 – Idle-time in /proc/uptime wrong

On my 2.6.30.5 kernel (custom compiled, x86_64), idle secs in /proc/uptime is counting magnitudes slower than it should. Can't say which kernel was last to work fine, took all my systems straight from 2.6.25.10 to 2.6.30.5 before I noticed this little bug.
/proc/uptime:
852863.53 1469.57
/proc/stat:
# user nice system idle iowait irq softirq
cpu 4071827 348323 9027259 312735370 13759721 514537 715147 0 0
cpu0 1005162 42263 1877666 79928559 2091566 147005 200858 0 0
cpu1 758446 101285 2262592 77679311 4350283 57242 83892 0 0
cpu2 1668611 96271 3056564 75858419 3995871 260496 356803 0 0
cpu3 639608 108504 1830437 79269081 3322001 49794 73594 0 0
Computing back from numbers in /proc/stat, the idletime in /proc/uptime should read 781838.43 instead of 1469.57

I'm not seeing this on a 2.6.31 kernel. Are you still seeing this with any more recent kernels?

Sorry john for the long delay in following up - I did not exactly rank this as high-priority and never noticed you posted a response.
Latest kernel I have running is a 2.6.31, and this oddity is definitely showing there.
[root@backup2 ~]# cat /proc/uptime; cat /proc/stat | grep cpu
2592026.88 2569.52
cpu 11818453 10108 22715895 959211273 40687278 976152 1473425 0 0
cpu0 3146061 1410 4115859 250600571 340377 381680 637221 0 0
cpu1 1126544 3014 3020324 251840161 3042936 69833 120339 0 0
cpu2 1385205 1235 2265371 254987993 555561 8976 18794 0 0
cpu3 6160643 4449 13314341 201782548 36748404 515663 697071 0 0
allcpuidle / numcores / kernelfreq = 959211273 / 4 / 100 = 2398028, this box only sees activity twice a day so about 90% idle CPU sounds perfect.

Johan: My apologies for such a long delay between updates. Just trying to run over the bug backlog.
I'm still unable to reproduce this on three different x86_64 machines.
That said, looking at the code, I can see that proc/stat and proc/uptime use different methods to calculate idle.

Created attachment 72181 [details] 
test patch to make /proc/uptime and /proc/stat use same idle calculation
Give this a whirl and let me know if it seems to resolve the issue.