[c-nsp] Varying CPU usage on 881

[Pelle]

Hi Rodeney.

> That graph is total usage so there may be another process that
> contributes that takes longer on the 881 that doesn't show up
> on the 1841. ie: checkheaps, etc...
>
> Watch 'sh proc cpu sorted' during one of those spikes and see
> if you see another process contributing.

That was my original theory as well, but there are no other
significant processes:

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 23%/18%; one minute: 14%; five minutes: 5%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1104       514       2147  2.21%  0.69%  0.23%   6 Virtual Exec
  60        4208       632       6658  3.19%  2.67%  1.06%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 23%/18%; one minute: 14%; five minutes: 5%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1136       519       2188  2.21%  0.69%  0.23%   6 Virtual Exec
  60        4260       639       6666  3.19%  2.67%  1.06%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 43%/40%; one minute: 16%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1168       524       2229  1.31%  0.74%  0.25%   6 Virtual Exec
  60        4292       644       6664  1.88%  2.61%  1.07%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 43%/40%; one minute: 16%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1200       529       2268  1.31%  0.74%  0.25%   6 Virtual Exec
  60        4332       650       6664  1.88%  2.61%  1.07%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 43%/40%; one minute: 16%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1228       534       2299  1.31%  0.74%  0.25%   6 Virtual Exec
  60        4372       656       6664  1.88%  2.61%  1.07%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 43%/40%; one minute: 16%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1260       539       2337  1.31%  0.74%  0.25%   6 Virtual Exec
  60        4404       661       6662  1.88%  2.61%  1.07%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 27%/23%; one minute: 17%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1292       544       2375  1.63%  0.82%  0.27%   6 Virtual Exec
  60        4484       673       6662  2.78%  2.62%  1.10%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 27%/23%; one minute: 17%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1324       549       2411  1.63%  0.82%  0.27%   6 Virtual Exec
  60        4532       680       6664  2.78%  2.62%  1.10%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 27%/23%; one minute: 17%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1360       554       2454  1.63%  0.82%  0.27%   6 Virtual Exec
  60        4572       686       6664  2.78%  2.62%  1.10%   0 COLLECT STAT COU

881_router#sh proc cpu | ex 0.00
CPU utilization for five seconds: 21%/17%; one minute: 18%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  51        1396       559       2497  1.72%  0.89%  0.30%   6 Virtual Exec
  60        4612       692       6664  2.62%  2.62%  1.12%   0 COLLECT STAT COU

(The captures are taken quite rapidly.)

It's the sudden peak from 18% to 40% and back down to 17% for the
_interrupt based traffic_ that puzzles me.

> Also, I don't think it applies here given the pps number you gave
> before.
>
> I usually see that when the rate is divisible by 4.

The same wavy CPU load occurs whatever traffic I throw at the router.

-- 
Pelle