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>Profiling functions</TITLE
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><H1
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><A
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><A
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NAME="PROFILE-FUNCTIONS">Chapter 52. Profiling functions</H1
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NAME="PROFILE-FUNCTIONS">Chapter 52. Profiling functions</H1
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><DIV
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><DIV
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CLASS="SECT1"
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CLASS="SECT1"
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><H1
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><H1
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CLASS="SECT1"
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CLASS="SECT1"
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><A
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><A
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NAME="SERVICES-PROFILE-API">API</H1
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NAME="SERVICES-PROFILE-API">API</H1
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><P
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><P
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>In order for profile data to be gathered for an application, the
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>In order for profile data to be gathered for an application, the
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program has to initiate the process.
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program has to initiate the process.
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Once started, execution histogram data will be collected in a
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Once started, execution histogram data will be collected in a
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dynamic memory buffer.
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dynamic memory buffer.
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This data can be uploaded to a host using <SPAN
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This data can be uploaded to a host using <SPAN
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CLASS="emphasis"
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CLASS="emphasis"
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><I
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><I
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CLASS="EMPHASIS"
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CLASS="EMPHASIS"
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>TFTP</I
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>TFTP</I
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></SPAN
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></SPAN
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>.
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>.
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A side effect of the upload of the data is that the histogram
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A side effect of the upload of the data is that the histogram
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is reset.
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is reset.
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This is useful, especially for high resolution histograms, since
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This is useful, especially for high resolution histograms, since
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the histogram data are collected as 16-bit counters which can be quickly
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the histogram data are collected as 16-bit counters which can be quickly
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saturated.
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saturated.
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For example, if the histogram is being collected at a rate of 10,000
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For example, if the histogram is being collected at a rate of 10,000
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samples per second, a hot spot in the program could saturate after
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samples per second, a hot spot in the program could saturate after
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only 6.5 seconds.</P
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only 6.5 seconds.</P
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><P
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><P
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> The API for the application profiling functions can be
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> The API for the application profiling functions can be
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found in the file <TT
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found in the file <TT
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CLASS="FILENAME"
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CLASS="FILENAME"
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><cyg/profile/profile.h></TT
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><cyg/profile/profile.h></TT
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>.</P
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>.</P
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><DIV
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><DIV
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CLASS="SECT2"
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CLASS="SECT2"
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><H2
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><H2
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CLASS="SECT2"
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CLASS="SECT2"
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><A
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><A
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NAME="SERVICES-PROFILE-API-PROFILE-ON">profile_on</H2
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NAME="SERVICES-PROFILE-API-PROFILE-ON">profile_on</H2
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><P
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><P
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>This function is used to initiate the gathering of the
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>This function is used to initiate the gathering of the
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runtime execution histogram data.</P
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runtime execution histogram data.</P
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><TABLE
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><TD
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><TD
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><PRE
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><PRE
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CLASS="PROGRAMLISTING"
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CLASS="PROGRAMLISTING"
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>void profile_on(void *start, void *end, int bucket_size, int resolution);</PRE
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>void profile_on(void *start, void *end, int bucket_size, int resolution);</PRE
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></TD
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></TD
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></TR
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></TABLE
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></TABLE
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><P
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><P
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>Calling this function will initiate execution profiling.
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>Calling this function will initiate execution profiling.
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An execution histogram is collected at the rate of
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An execution histogram is collected at the rate of
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<TT
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<TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>resolution</I
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>resolution</I
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></TT
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></TT
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> times per second.
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> times per second.
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The area between <TT
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The area between <TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>start</I
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>start</I
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></TT
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></TT
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> and <TT
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> and <TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>end</I
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>end</I
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></TT
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></TT
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>
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>
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will be divided up into a number of buckets, each representing
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will be divided up into a number of buckets, each representing
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<TT
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<TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>bucket_size</I
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>bucket_size</I
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></TT
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></TT
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>
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>
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program bytes in length. Using statistical sampling (via a high speed timer), when
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program bytes in length. Using statistical sampling (via a high speed timer), when
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the program counter is found to be within the range
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the program counter is found to be within the range
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<TT
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<TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>start</I
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>start</I
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></TT
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></TT
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>..<TT
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>..<TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>end</I
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>end</I
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></TT
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></TT
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>, the appropriate
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>, the appropriate
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bucket (histogram entry) will be incremented.</P
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bucket (histogram entry) will be incremented.</P
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><P
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><P
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>The choice of <TT
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>The choice of <TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>resolution</I
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>resolution</I
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></TT
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></TT
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> and <TT
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> and <TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>bucket_size</I
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>bucket_size</I
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></TT
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></TT
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>
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>
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control how large the data gathered will be, as well as how much overhead is
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control how large the data gathered will be, as well as how much overhead is
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encumbered for gathering the histogram.
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encumbered for gathering the histogram.
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Smaller values for <TT
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Smaller values for <TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>bucket_size</I
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>bucket_size</I
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></TT
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></TT
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> will garner better
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> will garner better
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results (<TT
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results (<TT
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CLASS="FUNCTION"
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CLASS="FUNCTION"
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>gprof</TT
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>gprof</TT
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> can more closely align the data with
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> can more closely align the data with
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actual function names) at the expense of a larger data buffer.</P
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actual function names) at the expense of a larger data buffer.</P
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><DIV
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CLASS="NOTE"
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><BLOCKQUOTE
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><BLOCKQUOTE
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><P
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><P
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><B
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><B
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>NOTE: </B
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>NOTE: </B
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>The value of <TT
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>The value of <TT
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CLASS="PARAMETER"
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CLASS="PARAMETER"
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><I
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><I
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>bucket_size</I
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>bucket_size</I
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></TT
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></TT
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> will be rounded up to a power of two.</P
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> will be rounded up to a power of two.</P
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