What is causing high CPU "system" time?

Issue

Constant CPU consumption of 20% of the CPU sys (kernel time).

procs -----------memory---------------- ---swap-- -----io---- --system-- -----cpu------
 r  b    swpd   free   buff     cache   si   so     bi    bo    in    cs us sy id wa st
13  1 3722308 472224  98212 166903616  123    0  93309  3836 15564 42670 12 31 57  1  0 05:01:01
 9  0 3721968 461912  98784 166957280   12    0 115933  1829 15050 42663 11 31 58  0  0 05:02:01
 9  0 3721964 470808  99244 166976288    0    0 119748  1775 15342 38101 10 27 63  0  0 05:03:01
 7  0 3721964 469164  99596 166965280    0    0 116719  1791 15195 36408 10 26 64  0  0 05:04:01
12  0 3721964 454212 100004 166962944    0    0 117444  1632 16523 41308  9 26 64  0  0 05:05:01
10  0 3721964 483584  99748 166882400    0    0 113418  1781 16821 43998 10 27 64  0  0 05:06:01
 9  0 3721968 460820  99848 166923040    0    0 122266  1770 18985 63617 10 27 63  0  0 05:07:01
 9  0 3721968 455848  99872 166933360    0    0 179514  1650 19263 68173 10 27 63  0  0 05:08:01
 6  0 3721964 458844  99724 166970496    0    0 119711  1624 20101 46560  9 23 67  0  0 05:09:01
 6  0 3721964 475580  99712 167005792    0    0 136124  1649 28558 68558  9 23 68  0  0 05:10:01
 9  0 3722156 466828 100068 167017248    1    1 118878  1674 27738 64769 10 24 66  0  0 05:11:01
 9  0 3722240 455664 100156 167035616    0    0 116729  1768 17742 35043  9 22 69  0  0 05:12:01
 6  0 3722300 453596 100340 167044560    0    0 143485  1515 20246 41549  9 22 69  0  0 05:13:01
11  0 3722300 460668  99956 167010416    0    0 168932  1644 19711 53847  9 21 70  0  0 05:14:01
 6  0 3722300 465712  97724 167001088    0    0 209824  1745 19885 69023  9 22 69  0  0 05:15:01
10  0 3722288 462160  97576 166991440    1    0 172998  1767 19013 67610  9 22 69  0  0 05:16:01