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-><DIV
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-><H1
-><A
-NAME="PROFILE-FUNCTIONS">Chapter 52. Profiling functions</H1
-><DIV
-CLASS="SECT1"
-><H1
-CLASS="SECT1"
-><A
-NAME="SERVICES-PROFILE-API">API</H1
-><P
->In order for profile data to be gathered for an application, the
-program has to initiate the process.
-Once started, execution histogram data will be collected in a
-dynamic memory buffer.
-This data can be uploaded to a host using <SPAN
-CLASS="emphasis"
-><I
-CLASS="EMPHASIS"
->TFTP</I
-></SPAN
->.
-A side effect of the upload of the data is that the histogram
-is reset.
-This is useful, especially for high resolution histograms, since
-the histogram data are collected as 16-bit counters which can be quickly
-saturated.
-For example, if the histogram is being collected at a rate of 10,000
-samples per second, a hot spot in the program could saturate after
-only 6.5 seconds.</P
-><P
-> The API for the application profiling functions can be
-found in the file <TT
-CLASS="FILENAME"
-><cyg/profile/profile.h></TT
->.</P
-><DIV
-CLASS="SECT2"
-><H2
-CLASS="SECT2"
-><A
-NAME="SERVICES-PROFILE-API-PROFILE-ON">profile_on</H2
-><P
->This function is used to initiate the gathering of the
-runtime execution histogram data.</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
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-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->void profile_on(void *start, void *end, int bucket_size, int resolution);</PRE
-></TD
-></TR
-></TABLE
-><P
->Calling this function will initiate execution profiling.
-An execution histogram is collected at the rate of
-<TT
-CLASS="PARAMETER"
-><I
->resolution</I
-></TT
-> times per second.
-The area between <TT
-CLASS="PARAMETER"
-><I
->start</I
-></TT
-> and <TT
-CLASS="PARAMETER"
-><I
->end</I
-></TT
->
-will be divided up into a number of buckets, each representing
-<TT
-CLASS="PARAMETER"
-><I
->bucket_size</I
-></TT
->
-program bytes in length. Using statistical sampling (via a high speed timer), when
-the program counter is found to be within the range
-<TT
-CLASS="PARAMETER"
-><I
->start</I
-></TT
->..<TT
-CLASS="PARAMETER"
-><I
->end</I
-></TT
->, the appropriate
-bucket (histogram entry) will be incremented.</P
-><P
->The choice of <TT
-CLASS="PARAMETER"
-><I
->resolution</I
-></TT
-> and <TT
-CLASS="PARAMETER"
-><I
->bucket_size</I
-></TT
->
-control how large the data gathered will be, as well as how much overhead is
-encumbered for gathering the histogram.
-Smaller values for <TT
-CLASS="PARAMETER"
-><I
->bucket_size</I
-></TT
-> will garner better
-results (<TT
-CLASS="FUNCTION"
->gprof</TT
-> can more closely align the data with
-actual function names) at the expense of a larger data buffer.</P
-><DIV
-CLASS="NOTE"
-><BLOCKQUOTE
-CLASS="NOTE"
-><P
-><B
->NOTE: </B
->The value of <TT
-CLASS="PARAMETER"
-><I
->bucket_size</I
-></TT
-> will be rounded up to a power of two.</P
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