LTTng » Babeltrace

Add an option to Babeltrace so that it outputs the time stamps as clock cycle numbers.

I think LTTng 2 always sets a CTF clock frequency of 1 GHz, e.g.

clock {
        name = monotonic;
        uuid = "02fe53bd-4587-4704-b407-7d50c98c4d9b";
        description = "Monotonic Clock";
        freq = 1000000000; /* Frequency, in Hz */
        /* clock value offset from Epoch is: offset * (1/freq) */
        offset = 1337698044153589431;
};

and thus the time stamp unit is naturally the nanosecond. In this case, and in any case where the clock frequency is 10^x, the clock cycle can be seen in Babeltrace using --clock-raw and --clock-seconds:

[1735914.880434233] (+0.000000387) softirq_exit: { 2 }, { vec = 9 }

Here, 1735914.880434233 seconds means 1735914880434233 ns and since the frequency is 1 GHz, this means clock cycle 1735914880434233.

For other clock frequencies (CTF bare-metal tracing, etc.), it's impossible to get the exact clock cycles of events.

Note: clock cycles here are not necessarily CPU cycles (depends on the declared CTF clock frequency), but can be.

Suggestion to add a --clock-cycles (mutually exclusive from --clock-seconds) option to Babeltrace that makes it output the time stamps as plain integers (original clock cycles).