This changes effectively:
> go test ./go/types/perf ./samples/csv/csv-import <etc>
to:
> go test ./go/types/perf <etc>
> go test ./samples/csv/csv-import <etc>
The perf results started going crazy when I started running a second
test package (./go/types/perf), this is one reason why it may have
happened. It's hard to say for sure what go test is doing.