What do time fields in CounterSample mean?

Question

I have an instance of PerformanceCounter, I call NextSample() on it and get a CounterSample. In it, there are several time-related fields: CounterFrequency, SystemFrequency, CounterTimeStamp, Timestamp and TimeStamp100nSec.

The MSDN page for CounterSample only says "Gets the raw counter frequency" and similar unhelpful descriptions, and a sample that prints the value without explanations.

• What do these mean exactly?
• In what units are they? I tried all DateTime.FromX() functions, but none produces a reasonable result.

Answer 1

(sample2.Timestamp - sample1.Timestamp) / sample2.SystemFrequency = elapsed seconds

(sample2.TimeStamp100nSec - sample1.TimeStamp100nSec) / 10000000 = elapsed seconds

I was able to reverse engineer this when I was analyzing how LOGMAN.EXE would read perf counters and store them in a SQL database. CounterSample class (from various disassemblies) wraps this C structure

PDH_RAW_COUNTER

In this C structure, SecondValue has either TimeStamp or TimeStamp100nSec depending on the counter type. By the time it gets wrapped in .NET CounterSample struct, you can get either via the properties.