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glibc/benchtests/README
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Using the glibc microbenchmark suite | |
==================================== | |
The glibc microbenchmark suite automatically generates code for specified | |
functions, builds and calls them repeatedly for given inputs to give some | |
basic performance properties of the function. | |
Running the benchmark: | |
===================== | |
The benchmark needs python 2.7 or later in addition to the | |
dependencies required to build the GNU C Library. One may run the | |
benchmark by invoking make as follows: | |
$ make bench | |
This runs each function for 10 seconds and appends its output to | |
benchtests/bench.out. To ensure that the tests are rebuilt, one could run: | |
$ make bench-clean | |
The duration of each test can be configured setting the BENCH_DURATION variable | |
in the call to make. One should run `make bench-clean' before changing | |
BENCH_DURATION. | |
$ make BENCH_DURATION=1 bench | |
The benchmark suite does function call measurements using architecture-specific | |
high precision timing instructions whenever available. When such support is | |
not available, it uses clock_gettime (CLOCK_PROCESS_CPUTIME_ID). One can force | |
the benchmark to use clock_gettime by invoking make as follows: | |
$ make USE_CLOCK_GETTIME=1 bench | |
Again, one must run `make bench-clean' before changing the measurement method. | |
Adding a function to benchtests: | |
=============================== | |
If the name of the function is `foo', then the following procedure should allow | |
one to add `foo' to the bench tests: | |
- Append the function name to the bench variable in the Makefile. | |
- Make a file called `foo-inputs` to provide the definition and input for the | |
function. The file should have some directives telling the parser script | |
about the function and then one input per line. Directives are lines that | |
have a special meaning for the parser and they begin with two hashes '##'. | |
The following directives are recognized: | |
- args: This should be assigned a colon separated list of types of the input | |
arguments. This directive may be skipped if the function does not take any | |
inputs. One may identify output arguments by nesting them in <>. The | |
generator will create variables to get outputs from the calling function. | |
- ret: This should be assigned the type that the function returns. This | |
directive may be skipped if the function does not return a value. | |
- includes: This should be assigned a comma-separated list of headers that | |
need to be included to provide declarations for the function and types it | |
may need (specifically, this includes using "#include <header>"). | |
- include-sources: This should be assigned a comma-separated list of source | |
files that need to be included to provide definitions of global variables | |
and functions (specifically, this includes using "#include "source"). | |
See pthread_once-inputs and pthreads_once-source.c for an example of how | |
to use this to benchmark a function that needs state across several calls. | |
- init: Name of an initializer function to call to initialize the benchtest. | |
- name: See following section for instructions on how to use this directive. | |
Lines beginning with a single hash '#' are treated as comments. See | |
pow-inputs for an example of an input file. | |
Multiple execution units per function: | |
===================================== | |
Some functions have distinct performance characteristics for different input | |
domains and it may be necessary to measure those separately. For example, some | |
math functions perform computations at different levels of precision (64-bit vs | |
240-bit vs 768-bit) and mixing them does not give a very useful picture of the | |
performance of these functions. One could separate inputs for these domains in | |
the same file by using the `name' directive that looks something like this: | |
##name: 240bit | |
See the pow-inputs file for an example of what such a partitioned input file | |
would look like. | |
Benchmark Sets: | |
============== | |
In addition to standard benchmarking of functions, one may also generate | |
custom outputs for a set of functions. This is currently used by string | |
function benchmarks where the aim is to compare performance between | |
implementations at various alignments and for various sizes. | |
To add a benchset for `foo': | |
- Add `foo' to the benchset variable. | |
- Write your bench-foo.c that prints out the measurements to stdout. | |
- On execution, a bench-foo.out is created in $(objpfx) with the contents of | |
stdout. |