This is the vmstat output when the high load peak happens:
# vmstat 3
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy
id wa
54 1 756868 1047128 264572 341573472 0 0 243 272 1 2 51 7
39 2
53 1 756888 924452 264508 341566080 0 7 31379 3623 53110 184808
29 55 15 1
70 1 756892 992416 264408 341530880 0 3 14483 9455 53010 183758
23 61 15 1
93 1 756900 954704 264160 341514208 0 3 20280 3391 66607 304526
23 59 17 1
65 2 756916 998524 263696 341427520 0 5 23295 2084 53748 213259
26 60 12 1
46 0 756924 969036 263636 341421088 0 3 23508 1447 51134 200739
22 59 19 1
123 1 756932 977336 263568 341426016 0 3 21444 2747 48044 174390
27 59 13 1
71 2 756932 975932 263580 341483520 0 0 19328 89629 54321 234718
25 59 14 2
47 5 756932 967004 263676 341502240 0 0 19509 52652 56792 236648
21 60 15 4
70 0 756944 1038464 263660 341468800 0 4 21349 3584 51937 179806
25 59 15 1
70 0 756940 923800 263532 341475712 0 0 15135 1524 58201 236794
21 59 19 1
40 1 756940 1022420 263560 341506560 0 0 9163 4889 34702 130106
19 61 19 1
59 0 756944 939380 263500 341518144 0 1 22809 4024 46398 224644
21 60 19 1
56 1 756956 954656 263464 341469440 0 4 22927 4477 53705 175386
28 57 14 1
39 0 756976 968204 263372 341376576 0 7 24612 2556 61900 262784
30 51 18 1
109 1 756984 1015260 263332 341323776 0 3 16636 4039 29271
83699 7 85 7 1
76 6 756992 980044 263312 341308128 0 3 6949 1848 27496 130478
6 90 2 2
103 0 756992 963540 263308 341352064 0 0 22125 2493 20526 61133
4 88 6 2
Seems most of the cpu is used by sys part.