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Subject: bug#21765: 24.5; Profiler innefective for recursive functions
Resent-From: Jonathan H <pythonnut@HIDDEN>
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From: Jonathan H <pythonnut@HIDDEN>
Date: Mon, 26 Oct 2015 10:47:01 -0700
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The Emacs profiler cannot be used to effectively profile, because the
reports do not flatten the recursion.

Take for example, this recipie:

;; Naive Fibonacci has terrible time complexity.
(defun fib (n)
  (if (< n 3)
      1
    (+ (fib (- n 1))
       (fib (- n 2)))))

(profiler-start 'cpu)
(fib 30)
(profiler-report)
(profiler-stop)

Here, The profiler report assigns (nearly) all of the time to (+ ...),
including time from deeper invocations of fib (and their invocations of (+
...), which makes the profiling report less-than-optimal.

Thanks,
PythonNut

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<div dir=3D"ltr">The Emacs profiler cannot be used to effectively profile, =
because the reports do not flatten the recursion.<br><div><div><div><br></d=
iv><div>Take for example, this recipie:<br></div><div><br></div><div>;; Nai=
ve Fibonacci has terrible time complexity. <br></div><div>(defun fib (n)<br=
>=C2=A0 (if (&lt; n 3)<br>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 1<br>=C2=A0=C2=A0=
=C2=A0 (+ (fib (- n 1))<br>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (fib (- n 2=
)))))<br><br>(profiler-start &#39;cpu)<br>(fib 30)<br>(profiler-report)<br>=
(profiler-stop)<br><br></div><div>Here, The profiler report assigns (nearly=
) all of the time to (+ ...), including time from deeper invocations of fib=
 (and their invocations of (+ ...), which makes the profiling report less-t=
han-optimal.<br><br></div><div>Thanks,<br></div><div>PythonNut<br></div></d=
iv></div></div>

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X-Loop: help-debbugs@HIDDEN
From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: Jonathan H <pythonnut@HIDDEN>
Subject: bug#21765: Acknowledgement (24.5; Profiler innefective for
 recursive functions)
Message-ID: <handler.21765.B.144588167717879.ack <at> debbugs.gnu.org>
References: <CAAW2-ZeCiD27dPe47JC=ZM-cyVZVjecgmhuDnaTFOeqbjH2VjQ@HIDDEN>
X-Gnu-PR-Message: ack 21765
X-Gnu-PR-Package: emacs
Reply-To: 21765 <at> debbugs.gnu.org
Date: Mon, 26 Oct 2015 17:48:02 +0000

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