[OpenSPARC-T2-SAM] / sam-t2 / devtools / amd64 / html / python / lib / profile-calibration.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="next" href="node458.html" />
<link rel="prev" href="profile-limits.html" />
<link rel="parent" href="profile.html" />
<link rel="next" href="node458.html" />
<meta name='aesop' content='information' />
<title>10.7 Calibration </title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="10.6 Limitations"
  href="profile-limits.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="10. The Python Profiler"
  href="profile.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="10.8 Extensions  "
  href="node458.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="profile-limits.html">10.6 Limitations</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="profile.html">10. The Python Profiler</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="node458.html">10.8 Extensions  </A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->

<H1><A NAME="SECTION0012700000000000000000"></A><A NAME="profile-calibration"></A>
<BR>
10.7 Calibration 
</H1>

<P>
The profiler subtracts a constant from each
event handling time to compensate for the overhead of calling the time
function, and socking away the results.  By default, the constant is 0.
The following procedure can
be used to obtain a better constant for a given platform (see discussion
in section Limitations above).

<P>
<div class="verbatim"><pre>
import profile
pr = profile.Profile()
for i in range(5):
    print pr.calibrate(10000)
</pre></div>

<P>
The method executes the number of Python calls given by the argument,
directly and again under the profiler, measuring the time for both.
It then computes the hidden overhead per profiler event, and returns
that as a float.  For example, on an 800 MHz Pentium running
Windows 2000, and using Python's time.clock() as the timer,
the magical number is about 12.5e-6.

<P>
The object of this exercise is to get a fairly consistent result.
If your computer is <em>very</em> fast, or your timer function has poor
resolution, you might have to pass 100000, or even 1000000, to get
consistent results.

<P>
When you have a consistent answer,
there are three ways you can use it:<A NAME="tex2html52"
  HREF="#foot46353"><SUP>10.3</SUP></A>
<P>
<div class="verbatim"><pre>
import profile

# 1. Apply computed bias to all Profile instances created hereafter.
profile.Profile.bias = your_computed_bias

# 2. Apply computed bias to a specific Profile instance.
pr = profile.Profile()
pr.bias = your_computed_bias

# 3. Specify computed bias in instance constructor.
pr = profile.Profile(bias=your_computed_bias)
</pre></div>

<P>
If you have a choice, you are better off choosing a smaller constant, and
then your results will ``less often'' show up as negative in profile
statistics.

<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot46353">... it:</A><A
 href="profile-calibration.html#tex2html52"><SUP>10.3</SUP></A></DT>
<DD>Prior to Python 2.2, it
  was necessary to edit the profiler source code to embed the bias as
  a literal number.  You still can, but that method is no longer
  described, because no longer needed.

</DD>
</DL>
<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="10.6 Limitations"
  href="profile-limits.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="10. The Python Profiler"
  href="profile.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="10.8 Extensions  "
  href="node458.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="profile-limits.html">10.6 Limitations</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="profile.html">10. The Python Profiler</A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="node458.html">10.8 Extensions  </A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>
Commit	Line	Data
920dae64 AT	1	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
	2	<html>
	3	<head>
	4	<link rel="STYLESHEET" href="lib.css" type='text/css' />
	5	<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
	6	<link rel='start' href='../index.html' title='Python Documentation Index' />
	7	<link rel="first" href="lib.html" title='Python Library Reference' />
	8	<link rel='contents' href='contents.html' title="Contents" />
	9	<link rel='index' href='genindex.html' title='Index' />
	10	<link rel='last' href='about.html' title='About this document...' />
	11	<link rel='help' href='about.html' title='About this document...' />
	12	<link rel="next" href="node458.html" />
	13	<link rel="prev" href="profile-limits.html" />
	14	<link rel="parent" href="profile.html" />
	15	<link rel="next" href="node458.html" />
	16	<meta name='aesop' content='information' />
	17	<title>10.7 Calibration </title>
	18	</head>
	19	<body>
	20	<DIV CLASS="navigation">
	21	<div id='top-navigation-panel' xml:id='top-navigation-panel'>
	22	<table align="center" width="100%" cellpadding="0" cellspacing="2">
	23	<tr>
	24	<td class='online-navigation'><a rel="prev" title="10.6 Limitations"
	25	href="profile-limits.html"><img src='../icons/previous.png'
	26	border='0' height='32' alt='Previous Page' width='32' /></A></td>
	27	<td class='online-navigation'><a rel="parent" title="10. The Python Profiler"
	28	href="profile.html"><img src='../icons/up.png'
	29	border='0' height='32' alt='Up One Level' width='32' /></A></td>
	30	<td class='online-navigation'><a rel="next" title="10.8 Extensions "
	31	href="node458.html"><img src='../icons/next.png'
	32	border='0' height='32' alt='Next Page' width='32' /></A></td>
	33	<td align="center" width="100%">Python Library Reference</td>
	34	<td class='online-navigation'><a rel="contents" title="Table of Contents"
	35	href="contents.html"><img src='../icons/contents.png'
	36	border='0' height='32' alt='Contents' width='32' /></A></td>
	37	<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
	38	border='0' height='32' alt='Module Index' width='32' /></a></td>
	39	<td class='online-navigation'><a rel="index" title="Index"
	40	href="genindex.html"><img src='../icons/index.png'
	41	border='0' height='32' alt='Index' width='32' /></A></td>
	42	</tr></table>
	43	<div class='online-navigation'>
	44	<b class="navlabel">Previous:</b>
	45	<a class="sectref" rel="prev" href="profile-limits.html">10.6 Limitations</A>
	46	<b class="navlabel">Up:</b>
	47	<a class="sectref" rel="parent" href="profile.html">10. The Python Profiler</A>
	48	<b class="navlabel">Next:</b>
	49	<a class="sectref" rel="next" href="node458.html">10.8 Extensions </A>
	50	</div>
	51	<hr /></div>
	52	</DIV>
	53	<!--End of Navigation Panel-->
	54
	55	<H1><A NAME="SECTION0012700000000000000000"></A><A NAME="profile-calibration"></A>
	56	<BR>
	57	10.7 Calibration
	58	</H1>
	59
	60	<P>
	61	The profiler subtracts a constant from each
	62	event handling time to compensate for the overhead of calling the time
	63	function, and socking away the results. By default, the constant is 0.
	64	The following procedure can
65	be used to obtain a better constant for a given platform (see discussion
66	in section Limitations above).
67
68	<P>
69	<div class="verbatim"><pre>
70	import profile
71	pr = profile.Profile()
72	for i in range(5):
73	print pr.calibrate(10000)
74	</pre></div>
75
76	<P>
77	The method executes the number of Python calls given by the argument,
78	directly and again under the profiler, measuring the time for both.
79	It then computes the hidden overhead per profiler event, and returns
80	that as a float. For example, on an 800 MHz Pentium running
81	Windows 2000, and using Python's time.clock() as the timer,
82	the magical number is about 12.5e-6.
83
84	<P>
85	The object of this exercise is to get a fairly consistent result.
86	If your computer is <em>very</em> fast, or your timer function has poor
87	resolution, you might have to pass 100000, or even 1000000, to get
88	consistent results.
89
90	<P>
91	When you have a consistent answer,
92	there are three ways you can use it:<A NAME="tex2html52"
93	HREF="#foot46353"><SUP>10.3</SUP></A>
94	<P>
95	<div class="verbatim"><pre>
96	import profile
97
98	# 1. Apply computed bias to all Profile instances created hereafter.
99	profile.Profile.bias = your_computed_bias
100
101	# 2. Apply computed bias to a specific Profile instance.
102	pr = profile.Profile()
103	pr.bias = your_computed_bias
104
105	# 3. Specify computed bias in instance constructor.
106	pr = profile.Profile(bias=your_computed_bias)
107	</pre></div>
108
109	<P>
110	If you have a choice, you are better off choosing a smaller constant, and
111	then your results will ``less often'' show up as negative in profile
112	statistics.
113
114	<P>
115	<BR><HR><H4>Footnotes</H4>
116	<DL>
117	<DT><A NAME="foot46353">... it:</A><A
118	href="profile-calibration.html#tex2html52"><SUP>10.3</SUP></A></DT>
119	<DD>Prior to Python 2.2, it
120	was necessary to edit the profiler source code to embed the bias as
121	a literal number. You still can, but that method is no longer
122	described, because no longer needed.
123
124	</DD>
125	</DL>
126	<DIV CLASS="navigation">
127	<div class='online-navigation'>
128	<p></p><hr />
129	<table align="center" width="100%" cellpadding="0" cellspacing="2">
130	<tr>
131	<td class='online-navigation'><a rel="prev" title="10.6 Limitations"
132	href="profile-limits.html"><img src='../icons/previous.png'
133	border='0' height='32' alt='Previous Page' width='32' /></A></td>
134	<td class='online-navigation'><a rel="parent" title="10. The Python Profiler"
135	href="profile.html"><img src='../icons/up.png'
136	border='0' height='32' alt='Up One Level' width='32' /></A></td>
137	<td class='online-navigation'><a rel="next" title="10.8 Extensions "
138	href="node458.html"><img src='../icons/next.png'
139	border='0' height='32' alt='Next Page' width='32' /></A></td>
140	<td align="center" width="100%">Python Library Reference</td>
141	<td class='online-navigation'><a rel="contents" title="Table of Contents"
142	href="contents.html"><img src='../icons/contents.png'
143	border='0' height='32' alt='Contents' width='32' /></A></td>
144	<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
145	border='0' height='32' alt='Module Index' width='32' /></a></td>
146	<td class='online-navigation'><a rel="index" title="Index"
147	href="genindex.html"><img src='../icons/index.png'
148	border='0' height='32' alt='Index' width='32' /></A></td>
149	</tr></table>
150	<div class='online-navigation'>
151	<b class="navlabel">Previous:</b>
152	<a class="sectref" rel="prev" href="profile-limits.html">10.6 Limitations</A>
153	<b class="navlabel">Up:</b>
154	<a class="sectref" rel="parent" href="profile.html">10. The Python Profiler</A>
155	<b class="navlabel">Next:</b>
156	<a class="sectref" rel="next" href="node458.html">10.8 Extensions </A>
157	</div>
158	</div>
159	<hr />
160	<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
161	</DIV>
162	<!--End of Navigation Panel-->
163	<ADDRESS>
164	See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
165	</ADDRESS>
166	</BODY>
167	</HTML>