Improved speed of hex parsing in more places #227
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Xyene
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…f maps with int64_of_hex_string. This addresses issue janestreet#93. Although janestreet#150 implemented fast hex string parsing, when I was magic-tracing magic-trace, I noticed unexpected lengthy calls to `Scanf` and related functions. This occurs because of calling `Int.Hex.of_string offset` within `parse_symbol_and_offset`. And this tends to take around 200-250 ns. Since this occurs about once per line in the `perf.data` file, the trace I ran this on executed this around 1.8 million times which should save a few hundred ms (out of total time of a few seconds). On traces after and before this change (respectively) of 3 decodes (which contain 3 executions of `parse_symbol_and_offset`) of a perf line containing an entry of the callstack sampled. The former is just below 2 us and the latter is around 2.6 us. However it is clear that most of the remaining time is now spent on evaluating regex in the former. In regards to implementation, I extracted these functions out to a `Util` module and used them when possible else where in magic-trace (although only the offset calculation is expensive because it is called a lot, but it seems reasonable to use them if possible). I used first class modules to abstract around `Int` and `Int64`. Signed-off-by: Aaron Lamoreaux <alamoreaux@janestreet.com>
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This addresses issue #93. Although #150 implemented fast hex string parsing, when I was magic-tracing magic-trace, I noticed this in the trace:
This section of the trace entirely occurs because of calling
Int.Hex.of_string offsetwithinparse_symbol_and_offset. And this tends to take around 200-250 ns. Since this occurs about once per line in theperf.datafile, the trace I ran this on executed this around 1.8 million times which should save a few hundred ms (out of total time of a few seconds).Here are the traces after and before this change (respectively) zoomed in on 3 decodes (which shows 3 executions of
parse_symbol_and_offset) of a perf line containing an entry of the callstack sampled. The former is just below 2 us and the latter is around 2.6 us. However it is clear that most of the remaining time is now spent on evaluating regex in the former.In regards to implementation, I extracted these functions out to a
Utilmodule and used them when possible else where in magic-trace (although only the offset calculation is expensive because it is called a lot, but it seems reasonable to use them if possible). I used first class modules to abstract aroundIntandInt64.