67 lines
2.4 KiB
Markdown
67 lines
2.4 KiB
Markdown
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# perf Module
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This module provides simple performance measurement for an application.
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It samples the program counter roughly every 50 microseconds and builds
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a histogram of the values that it finds. Since there is only a small amount
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of memory to store the histogram, the user can specify which area of code
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is of interest. The default is the enitre flash which contains code. Once the hotspots are
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identified, then the run can then be repeated with different areas and at different
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resolutions to get as much information as required.
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## perf.start()
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Starts a performance monitoring session.
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#### Syntax
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`perf.start([start[, end[, nbins[, offset]]]])`
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#### Parameters
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- `start` (optional) The lowest PC address for the histogram. Default is 0x40000000.
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- `end` (optional) The highest address for the histogram. Default is the end of the used space in the flash memory.
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- `nbins` (optional) The number of bins in the histogram. Keep this reasonable otherwise
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you will run out of memory. Default is 1024.
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- `offset` (Very optional) This specifies the offset of the saved PC value
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on the interrupt stack. It appears that 20 is the correct value.
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Note that the number of bins is an upper limit. The size of each bin is set to be the smallest power of two
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such that the number of bins required is less than or equal to the provided number of bins.
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#### Returns
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Nothing
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## perf.stop()
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Terminates a performance monitoring session and returns the histogram.
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#### Syntax
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`total, outside, histogram, binsize = perf.stop()`
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#### Returns
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- `total` The total number of samples captured in this run
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- `outside` The number of samples that were outside the histogram range
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- `histogram` The histogram represented as a table indexed by address where the value is the number of samples. The address is the lowest address for the bin.
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- `binsize` The number of bytes per histogram bin.
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### Example
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perf.start()
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for j = 0, 100 do
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str = "str"..j
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end
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tot, out, tbl, binsize = perf.stop()
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print(tot, out)
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local keyset = {}
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local n = 0
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for k,v in pairs(tbl) do
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n=n+1
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keyset[n]=k
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end
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table.sort(keyset)
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for kk,k in ipairs(keyset) do print(string.format("%x - %x",k, k + binsize - 1),tbl[k]) end
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This runs a loop creating strings 100 times and then prints out the histogram (after sorting it).
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This takes around 2,500 samples and provides a good indication of where all the CPU time is
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being spent.
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