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Application profiling
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Application profiling
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The profile_gprof package provides a mechanism to measure the
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The profile_gprof package provides a mechanism to measure the
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runtime performance of an application. This is done by gathering
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runtime performance of an application. This is done by gathering
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an execution histogram.
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an execution histogram.
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When profiling is started on the target device, a
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When profiling is started on the target device, a
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TFTP
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TFTP
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server will be started
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server will be started
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which exports the single file
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which exports the single file
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PROFILE.DAT
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PROFILE.DAT
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This analysis data can then be fetched
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This analysis data can then be fetched
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by connecting to the target with a TFTP
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by connecting to the target with a TFTP
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client program
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client program
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and then be processed by the
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and then be processed by the
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gprof
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gprof
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utility program.
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utility program.
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NOTE
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NOTE
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Be sure and specify binary mode transfers for this data file,
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Be sure and specify binary mode transfers for this data file,
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which may not be the default with on some TFTP
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which may not be the default with on some TFTP
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client programs.
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client programs.
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NOTE
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NOTE
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The port used for this TFTP server is
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The port used for this TFTP server is
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configurable. The default will be the IETF standard port
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configurable. The default will be the IETF standard port
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of 69/UDP, but it may be changed to any UDP port via the
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of 69/UDP, but it may be changed to any UDP port via the
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CYGNUM_PROFILE_TFTP_PORT CDL option.
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CYGNUM_PROFILE_TFTP_PORT CDL option.
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Profiling functions
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Profiling functions
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API
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API
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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 TFTP.
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This data can be uploaded to a host using TFTP.
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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.
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only 6.5 seconds.
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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 <cyg/profile/profile.h>.
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found in the file <cyg/profile/profile.h>.
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profile_on
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profile_on
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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.
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runtime execution histogram data.
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void profile_on(void *start, void *end, int bucket_size, int resolution);
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void profile_on(void *start, void *end, int bucket_size, int resolution);
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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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resolution times per second.
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resolution times per second.
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The area between start and end
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The area between start and end
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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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bucket_size
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bucket_size
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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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start..end, the appropriate
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start..end, the appropriate
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bucket (histogram entry) will be incremented.
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bucket (histogram entry) will be incremented.
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The choice of resolution and bucket_size
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The choice of resolution and bucket_size
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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 bucket_size will garner better
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Smaller values for bucket_size will garner better
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results (gprof can more closely align the data with
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results (gprof can more closely align the data with
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actual function names) at the expense of a larger data buffer.
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actual function names) at the expense of a larger data buffer.
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NOTE
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NOTE
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The value of bucket_size will be rounded up to a power of two.
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The value of bucket_size will be rounded up to a power of two.
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