Could the API documentation for perf-object-get-instances cover the proper handling of counter rollovers?
Some high-rate-of-change counters (e.g. system:system:disk_data_read, system:system:disk_data_write) are highly susceptible to rollover, and naive implementation of the SDK will result in some negative rates. At least for those, a negative value is nonsense, but I don't see where this assumption could be generalized.
Would it be correct that counters are always positively incrementing, in which case "Raw(T0) > Raw(T1)" would be sufficient? If not, is there a subset of counters (e.g. properties "rate" or "average") that could be expected to always be positive?