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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
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.