Runtime events tools

A collection of observability tools around the runtime events tracing system introduced in OCaml 5.0.

olly

olly provides a number of sub-commands.

gc-stats

olly gc-stats will report the GC running time and GC tail latency profile of an OCaml executable.

$ olly gc-stats 'binarytrees.exe 22' # Use quotes for commands with arguments
Execution times:
Wall time (s):  21.45
GC time (s):    14.33
GC overhead (% of wall time):   66.79%

GC latency profile:
#[Mean (ms):    0.92,    Stddev (ms):   1.54]
#[Min (ms):     0.00,    max (ms):      11.06]

Percentile       Latency (ms)
25.0000          0.00
50.0000          0.09
60.0000          0.42
70.0000          1.05
75.0000          1.33
80.0000          1.97
85.0000          2.22
90.0000          2.60
95.0000          3.45
96.0000          4.77
97.0000          6.52
98.0000          6.82
99.0000          7.20
99.9000          7.58
99.9900          7.86
99.9990          11.06
99.9999          11.06
100.0000         11.06

$ olly gc-stats 'menhir -v --table sysver.mly' # Use quotes for commands with arguments
<snip>
Execution times:
Wall time (s):  68.51
GC time (s):    9.15
GC overhead (% of wall time):   13.35%

GC latency profile:
#[Mean (ms):    0.13,    Stddev (ms):   0.56]
#[Min (ms):     0.00,    max (ms):      42.89]

Percentile       Latency (ms)
25.0000          0.00
50.0000          0.00
60.0000          0.00
70.0000          0.00
75.0000          0.01
80.0000          0.01
85.0000          0.01
90.0000          0.32
95.0000          0.87
96.0000          1.09
97.0000          1.35
98.0000          1.74
99.0000          2.35
99.9000          5.40
99.9900          16.34
99.9990          28.31
99.9999          42.89
100.0000         42.89

trace

olly trace will record the runtime trace log in Fuchsia trace format or Chrome tracing format . Format of the trace file can be specified with the --format option. The default is Fuchsia trace format.

$ olly trace --format=fuchsia menhir_sysver.trace 'menhir -v --table sysver.mly' # Fuchsia trace format
<snip>
$ ls menhir_sysver.trace
menhir_sysver.trace

$ olly trace --format=json menhir_sysver.trace 'menhir -v --table sysver.mly' # Chrome tracing format
<snip>
$ ls menhir_sysver.trace
menhir_sysver.trace

Traces in either formats can be viewed in perfetto trace viewer. Chrome format trace can also be viewed in chrome://tracing in chromium-based browsers.

Dependencies

The library depends on hdr_histogram_ocaml.