core_profiler
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package core_profiler
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Use this module for online tracking of perf metrics. When using this module, the metrics are written out to stdout every second. There is no mertric file generated for offline analysis. The rate at which metrics are dumped to stdout is controlled by the environment variable CORE_PROFILER=PRINT_INTERVAL=N where N is the integer number of seconds to wait between outputs.

Profiler.don't_check_env is a no-op, provided for compatibility with Offline's interface. Time_stamp_counter calibration is liable to happen occasionally when calling at. safe_to_delay checks if it will be necessary soon, and does it in advance. If possible, call safe_to_delay (fairly regularly) from a time-insensitive point in code (or at least, outside any deltas / groups) to reduce the number of spurious jumps in time deltas.

This is how much the online probes cost. I don't know how much I trust these metrics, but here they are:

  1. ./inline_benchmarks_runner -q 3 -mat online ┌─────────────────────────────────────────────────────┬──────────┬────────────┐ │ Name │ Time/Run │ Percentage │ ├─────────────────────────────────────────────────────┼──────────┼────────────┤ │ online.ml:Fstats:Fstats update_in_place │ 12.96ns │ 6.94% │ │ online.ml:Timer at │ 11.56ns │ 6.19% │ │ online.ml:Timer group_point_at (0 sources) │ 13.31ns │ 7.13% │ │ online.ml:Timer group_point_at (1 sources) │ 22.91ns │ 12.27% │ │ online.ml:Timer group_point_at (2 sources) │ 40.45ns │ 21.66% │ │ online.ml:Timer group_reset │ 11.58ns │ 6.20% │ │ online.ml:Probe at │ 17.94ns │ 9.61% │ │ online.ml:Probe group_point_at (0 sources) │ 12.03ns │ 6.44% │ │ online.ml:Probe group_point_at (1 sources) │ 21.35ns │ 11.43% │ │ online.ml:Probe group_point_at (2 sources) │ 32.17ns │ 17.22% │ │ online.ml:Probe group_reset │ 11.32ns │ 6.06% │ │ online.ml:Delta_timer start_async │ 11.52ns │ 6.17% │ │ online.ml:Delta_timer stop_async │ 21.99ns │ 11.77% │ │ online.ml:Delta_timer start │ 11.63ns │ 6.23% │ │ online.ml:Delta_timer stop │ 21.99ns │ 11.77% │ │ online.ml:Delta_timer.wrap_sync nop │ 2.87ns │ 1.54% │ │ online.ml:Delta_timer.wrap_sync wrapped_nop │ 45.51ns │ 24.37% │ │ online.ml:Delta_timer.wrap_sync count_256 │ 146.13ns │ 78.25% │ │ online.ml:Delta_timer.wrap_sync wrapped_count_256 │ 186.75ns │ 100.00% │ │ online.ml:Delta_probe start │ 3.16ns │ 1.69% │ │ online.ml:Delta_probe stop │ 17.59ns │ 9.42% │ │ online.ml:Delta_probe start_async │ 2.96ns │ 1.58% │ │ online.ml:Delta_probe stop_async │ 17.26ns │ 9.24% │ └─────────────────────────────────────────────────────┴──────────┴────────────┘
include Core_profiler_disabled.Intf.Profiler_intf with type Delta_timer.state = private Core.Time_ns.t and type Delta_probe.state = private int
module Profiler : sig ... end

A Timer contains only a time stamp and no extra information; however, it is useful because (in Offline) the current time is recorded when measurements are made.

A Probe records some integer value that is passed to at along with a timestamp.

module Delta_probe : sig ... end

Delta_probe is an optimized two-probe group to track changes to some counter.

module Delta_timer : sig ... end

Delta_timer is an optimized two-probe group to track time differences between calls to start and stop.