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75 lines
2.8 KiB
Plaintext
75 lines
2.8 KiB
Plaintext
Using the glibc microbenchmark suite
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====================================
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The glibc microbenchmark suite automatically generates code for specified
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functions, builds and calls them repeatedly for given inputs to give some
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basic performance properties of the function.
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Running the benchmark:
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=====================
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The benchmark can be executed by invoking make as follows:
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$ make bench
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This runs each function for 10 seconds and appends its output to
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benchtests/bench.out. To ensure that the tests are rebuilt, one could run:
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$ make bench-clean
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The duration of each test can be configured setting the BENCH_DURATION variable
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in the call to make. One should run `make bench-clean' before changing
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BENCH_DURATION.
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$ make BENCH_DURATION=1 bench
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The benchmark suite does function call measurements using architecture-specific
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high precision timing instructions whenever available. When such support is
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not available, it uses clock_gettime (CLOCK_PROCESS_CPUTIME_ID). One can force
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the benchmark to use clock_gettime by invoking make as follows:
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$ make USE_CLOCK_GETTIME=1 bench
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Again, one must run `make bench-clean' before changing the measurement method.
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Adding a function to benchtests:
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===============================
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If the name of the function is `foo', then the following procedure should allow
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one to add `foo' to the bench tests:
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- Append the function name to the bench variable in the Makefile.
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- Define foo-ARGLIST as a colon separated list of types of the input
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arguments. Use `void' if function does not take any inputs. Put in quotes
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if the input argument is a pointer, e.g.:
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malloc-ARGLIST: "void *"
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- Define foo-RET as the type the function returns. Skip if the function
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returns void. One could even skip foo-ARGLIST if the function does not
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take any inputs AND the function returns void.
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- Make a file called `foo-inputs` with one input value per line, an input
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being a comma separated list of arguments to be passed into the function.
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See pow-inputs for an example.
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The script that parses the -inputs file treats lines beginning with a single
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`#' as comments. Lines beginning with two hashes `##' are treated specially
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as `directives'.
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Multiple execution units per function:
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=====================================
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Some functions have distinct performance characteristics for different input
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domains and it may be necessary to measure those separately. For example, some
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math functions perform computations at different levels of precision (64-bit vs
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240-bit vs 768-bit) and mixing them does not give a very useful picture of the
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performance of these functions. One could separate inputs for these domains in
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the same file by using the `name' directive that looks something like this:
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##name: 240bit
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See the pow-inputs file for an example of what such a partitioned input file
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would look like.
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