Have anyone seen this kind of behaviour before with their load:
There is no obvious correlation between any of the indexing or search services that would be causing this, 99% of the time that is the 'normal' cpu usage that we see.
Occasionally, instead of the above 'normal' load, we get a load that is not spiky at all and when we do get this we see much better performance w.r.t searching.
Here's a picture of what that looks like, the drop in CPU usage is the interesting bit, the surrounding load is the normal load but 'smoothed' out due to how our metric storage works.
I hope this looks familiar to someone!