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* kb/perf-trace: api-trace.txt: add trace API documentation progress: simplify performance measurement by using getnanotime() wt-status: simplify performance measurement by using getnanotime() git: add performance tracing for git's main() function to debug scripts trace: add trace_performance facility to debug performance issues trace: add high resolution timer function to debug performance issues trace: add 'file:line' to all trace output trace: move code around, in preparation to file:line output trace: add current timestamp to all trace output trace: disable additional trace output for unit tests trace: add infrastructure to augment trace output with additional info sha1_file: change GIT_TRACE_PACK_ACCESS logging to use trace API Documentation/git.txt: improve documentation of 'GIT_TRACE*' variables trace: improve trace performance trace: remove redundant printf format attribute trace: consistently name the format parameter trace: move trace declarations from cache.h to new trace.h
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Original file line number | Diff line number | Diff line change |
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trace API | ||
========= | ||
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The trace API can be used to print debug messages to stderr or a file. Trace | ||
code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment | ||
variables. | ||
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||
The trace implementation automatically adds `timestamp file:line ... \n` to | ||
all trace messages. E.g.: | ||
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------------ | ||
23:59:59.123456 git.c:312 trace: built-in: git 'foo' | ||
00:00:00.000001 builtin/foo.c:99 foo: some message | ||
------------ | ||
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Data Structures | ||
--------------- | ||
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`struct trace_key`:: | ||
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Defines a trace key (or category). The default (for API functions that | ||
don't take a key) is `GIT_TRACE`. | ||
+ | ||
E.g. to define a trace key controlled by environment variable `GIT_TRACE_FOO`: | ||
+ | ||
------------ | ||
static struct trace_key trace_foo = TRACE_KEY_INIT(FOO); | ||
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static void trace_print_foo(const char *message) | ||
{ | ||
trace_print_key(&trace_foo, message); | ||
} | ||
------------ | ||
+ | ||
Note: don't use `const` as the trace implementation stores internal state in | ||
the `trace_key` structure. | ||
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Functions | ||
--------- | ||
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`int trace_want(struct trace_key *key)`:: | ||
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Checks whether the trace key is enabled. Used to prevent expensive | ||
string formatting before calling one of the printing APIs. | ||
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`void trace_disable(struct trace_key *key)`:: | ||
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Disables tracing for the specified key, even if the environment | ||
variable was set. | ||
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`void trace_printf(const char *format, ...)`:: | ||
`void trace_printf_key(struct trace_key *key, const char *format, ...)`:: | ||
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Prints a formatted message, similar to printf. | ||
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`void trace_argv_printf(const char **argv, const char *format, ...)``:: | ||
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Prints a formatted message, followed by a quoted list of arguments. | ||
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`void trace_strbuf(struct trace_key *key, const struct strbuf *data)`:: | ||
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Prints the strbuf, without additional formatting (i.e. doesn't | ||
choke on `%` or even `\0`). | ||
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`uint64_t getnanotime(void)`:: | ||
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Returns nanoseconds since the epoch (01/01/1970), typically used | ||
for performance measurements. | ||
+ | ||
Currently there are high precision timer implementations for Linux (using | ||
`clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`). | ||
Other platforms use `gettimeofday` as time source. | ||
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`void trace_performance(uint64_t nanos, const char *format, ...)`:: | ||
`void trace_performance_since(uint64_t start, const char *format, ...)`:: | ||
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Prints the elapsed time (in nanoseconds), or elapsed time since | ||
`start`, followed by a formatted message. Enabled via environment | ||
variable `GIT_TRACE_PERFORMANCE`. Used for manual profiling, e.g.: | ||
+ | ||
------------ | ||
uint64_t start = getnanotime(); | ||
/* code section to measure */ | ||
trace_performance_since(start, "foobar"); | ||
------------ | ||
+ | ||
------------ | ||
uint64_t t = 0; | ||
for (;;) { | ||
/* ignore */ | ||
t -= getnanotime(); | ||
/* code section to measure */ | ||
t += getnanotime(); | ||
/* ignore */ | ||
} | ||
trace_performance(t, "frotz"); | ||
------------ |
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