Argument distribution

[gomoripeti]

Instead of plotting latency of a function, plot the distribution of an
argument. Additionally it would be nice to plot a value derived from one or more
arguments. Deriving can happen in the match-spec (limited) or after passing all
the necessary arguments to an arbitrary "derive" fun which could be executed in
the trace handler.

The value

• int: in the simplest case must be an integer (with a lower and upper bound; default range can be 0..max_duration)
• enum: or any term with max number of combinations/buckets

Options:

• aggregation method: histogram (only integer; int) or frequency count (any term, enum)
• interval: how often to take a snapshot of the collected data (this is hard-coded currently for function latency to 1 second, but could make sense to set larger intervals in this case) (maybe does not need to be implemented)

http://manpages.ubuntu.com/manpages/zesty/man8/argdist-bpfcc.8.html

Query syntax

With the current syntax it would be possible to add extra action function:

mod:fun(_,A,_) -> argdist(A)
mod:fun(_,A,B) -> argdist(A+B)
mod:fun(_,A,_) -> argdist(A >= 0, enum)

Extended syntax:
(multiple lines for readability)

#argdist enum = 2,
    interval = "5sec",
    derive: if A > 0 -> positive; true -> neg_or_zero end,
    mfa = mod:fun(_, A, _)

%Argdist int: -100..100,
    interval: "5sec",
    mfa: Mod.fun(_, a, _)

Prerequisits:

• histogram/spectrogram visualisation ( Alternative histogram visualisation #107 )
• extended query syntax ( Extend query syntax #110 )