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tools api io: Move filling the io buffer to its own function

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In general a read fills 4kb so filling the buffer is a 1 in 4096
operation, move it out of the io__get_char function to avoid some
checking overhead and to better hint the function is good to inline.

For perf's IO intensive internal (non-rigorous) benchmarks there's a
small improvement to kallsyms-parsing with a default build.

Before:
```
$ perf bench internals all
Computing performance of single threaded perf event synthesis by
synthesizing events on the perf process itself:
  Average synthesis took: 146.322 usec (+- 0.305 usec)
  Average num. events: 61.000 (+- 0.000)
  Average time per event 2.399 usec
  Average data synthesis took: 145.056 usec (+- 0.155 usec)
  Average num. events: 329.000 (+- 0.000)
  Average time per event 0.441 usec

  Average kallsyms__parse took: 162.313 ms (+- 0.599 ms)
...
Computing performance of sysfs PMU event scan for 100 times
  Average core PMU scanning took: 53.720 usec (+- 7.823 usec)
  Average PMU scanning took: 375.145 usec (+- 23.974 usec)
```
After:
```
$ perf bench internals all
Computing performance of single threaded perf event synthesis by
synthesizing events on the perf process itself:
  Average synthesis took: 127.829 usec (+- 0.079 usec)
  Average num. events: 61.000 (+- 0.000)
  Average time per event 2.096 usec
  Average data synthesis took: 133.652 usec (+- 0.101 usec)
  Average num. events: 327.000 (+- 0.000)
  Average time per event 0.409 usec

  Average kallsyms__parse took: 150.415 ms (+- 0.313 ms)
...
Computing performance of sysfs PMU event scan for 100 times
  Average core PMU scanning took: 47.790 usec (+- 1.178 usec)
  Average PMU scanning took: 376.945 usec (+- 23.683 usec)
```

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240519181716.4088459-1-irogers@google.com
This commit is contained in:
Ian Rogers 2024-05-19 11:17:16 -07:00 committed by Namhyung Kim
parent f975c13d2a
commit d163d60258
1 changed files with 37 additions and 30 deletions
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25
tools/lib/api/io.h
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@ -43,17 +43,14 @@ static inline void io__init(struct io *io, int fd,
io->eof = false;
}
/* Reads one character from the "io" file with similar semantics to fgetc. */
static inline int io__get_char(struct io *io)
/* Read from fd filling the buffer. Called when io->data == io->end. */
static inline int io__fill_buffer(struct io *io)
{
char *ptr = io->data;
ssize_t n;
if (io->eof)
return -1;
if (ptr == io->end) {
ssize_t n;
if (io->timeout_ms != 0) {
struct pollfd pfds[] = {
{
@ -80,11 +77,21 @@ static inline int io__get_char(struct io *io)
io->eof = true;
return -1;
}
ptr = &io->buf[0];
io->data = &io->buf[0];
io->end = &io->buf[n];
return 0;
}
/* Reads one character from the "io" file with similar semantics to fgetc. */
static inline int io__get_char(struct io *io)
{
if (io->data == io->end) {
int ret = io__fill_buffer(io);
if (ret)
return ret;
}
io->data = ptr + 1;
return *ptr;
return *io->data++;
}
/* Read a hexadecimal value with no 0x prefix into the out argument hex. If the