Unexpectedly high latency spikes measured with hwlat

Question

I am using hwlat_detector tracer to measure system latencies that are caused outside the Linux.

The machine used for measurements is Asus Zenbook ux331un. I did disable processor power states with idle=poll kernel cmd-line parameter, hyper threading is disabled, turbo boost is disabled. Here is an example output of hwlat tracer.

   <...>-4976  [002] d......  3258.677286: #81    inner/outer(us):   31/33    ts:1572267806.608681762
   <...>-4976  [003] dn.....  3276.085073: #82    inner/outer(us):   32/34    ts:1572267824.016656104
   <...>-4976  [000] d.L....  3277.113063: #83    inner/outer(us):   32/0     ts:1572267825.044656725
   <...>-4976  [003] dn.....  3280.181030: #84    inner/outer(us):   32/32    ts:1572267828.112657027
   <...>-4976  [000] dnL....  3281.205020: #85    inner/outer(us):   32/32    ts:1572267829.136657127
   <...>-4976  [002] dn.....  3283.252999: #86    inner/outer(us):  456/33    ts:1572267831.184659048
   <...>-4976  [003] dn.....  3284.276986: #87    inner/outer(us):   16/32    ts:1572267832.208656275
   <...>-4976  [000] dnL....  3285.300975: #88    inner/outer(us):   16/33    ts:1572267833.232656714
   <...>-4976  [002] dn.....  3287.348959: #89    inner/outer(us):   20/33    ts:1572267835.280662760
   <...>-4976  [003] dn.....  3288.372943: #90    inner/outer(us):   33/34    ts:1572267836.304657092
   <...>-4976  [000] dnL....  3289.396938: #91    inner/outer(us):   32/32    ts:1572267837.328663631
   <...>-4976  [002] dn.....  3291.444912: #92    inner/outer(us):   20/33    ts:1572267839.376659443

As can be seen form the output, latency over 400us occurs.I am also getting a lot of latencies in 30us range. At first i thought that latencies are caused by SMIs, so i started to read MSR register 0x34 that counts the number of SMIs that occurred since the system was booted. It does not increase while the test is running. What else could be the reason for such latency?