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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.