gazagnaire.org
Logging, runtime tracing, and the obs performance profiler for OCaml
obs: extract memtrace report's derived predicates
merlint now measures functions inside functor bodies, and Model.report
lives in one. Its cyclomatic complexity (12) was driven by the boolean
operators of two derived flags, no_runtime_timing and no_evidence, computed
inline. Lift each to a named predicate above report. They are pure boolean
tests, which merlint does not count as control-flow complexity, and the
report body drops well under the threshold. No behaviour change.
author
Thomas Gazagnaire
date
(Jul 9, 2026, 6:33 AM UTC)
commit
4fffea75
4fffea75ae7837540311c36c6c4807bf136f9f23
parent
b31f65f5
b31f65f52ff9881940364102c6beb3824844b748
+20
-16
+20
-16
lib/obs/memtrace_eio.ml
+20
-16
lib/obs/memtrace_eio.ml
···
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(* A finding below [min_frac] of wall is not worth acting on (the "stop when
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the payoff is trivial" rule), so it is dropped before ranking. *)
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+
(* A trace with ocaml-probe spans but no GC-phase or Eio scheduler events:
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waiting and gc are structurally zero and cpu = wall by default, so the
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budget cannot be split and "CPU-bound" is never earned. Spans present with
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none of that timing is the signature; a runtime_events capture of an Eio or
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allocating program always carries fibers or GC slices. A bare allocating
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loop has no spans, so it keeps the residual CPU verdict. *)
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let no_runtime_timing t ~gc_time ~n_fibers ~n_ccs ~spans =
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gc_time = 0. && n_fibers = 0 && n_ccs = 0
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&& Hashtbl.length t.suspend_total = 0
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&& spans <> []
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+
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(* The meta file recorded a wall window but the runtime_events stream was
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empty and no memtrace samples arrived (mono_first never set): there is no
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event of any kind to attribute, so the leftover wall is unknown, not
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on-CPU. Distinct from no_runtime_timing, which still has spans. *)
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let no_evidence t ~wall_time =
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t.mono_first = None && t.total_alloc_words = 0 && wall_time > 0.
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+
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let report ?(min_frac = 0.1) t : Report.t =
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let now_ns = t.mono_last in
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flush_open_state t ~now_ns;
···
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List.sort (fun (a, _) (b, _) -> compare b a) !raw_findings
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|> List.mapi (fun i (_, f) -> { f with Report.rank = i + 1 })
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in
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-
(* A trace with ocaml-probe spans but no GC-phase or Eio scheduler events:
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waiting and gc are structurally zero and cpu = wall by default, so the
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budget cannot be split and "CPU-bound" is never earned. Spans present with
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none of that timing is the signature; a runtime_events capture of an Eio
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or allocating program always carries fibers or GC slices. A bare allocating
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loop has no spans, so it keeps the residual CPU verdict. *)
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let no_runtime_timing =
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gc_time = 0. && n_fibers = 0 && n_ccs = 0
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&& Hashtbl.length t.suspend_total = 0
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&& spans <> []
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no_runtime_timing t ~gc_time ~n_fibers ~n_ccs ~spans
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in
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(* The meta file recorded a wall window but the runtime_events stream was
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empty and no memtrace samples arrived (mono_first never set): there is no
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event of any kind to attribute, so the leftover wall is unknown, not
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on-CPU. Distinct from no_runtime_timing, which still has spans. *)
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let no_evidence =
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t.mono_first = None && t.total_alloc_words = 0 && wall_time > 0.
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in
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let no_evidence = no_evidence t ~wall_time in
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let verdict =
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compute_verdict ~allocation_only ~no_runtime_timing ~no_evidence ~findings
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~frac ~waiting ~gc_frac ~cpu