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This is the initial support for string function performance tests, along with copying tests for memcpy and memcpy-ifunc as proof of concept. The string function benchmarks perform operations at different alignments and for different sizes and compare performance between plain operations and the optimized string operations. Due to this their output is incompatible with the function benchmarks where we're interested in fastest time, throughput, etc. In future, the correctness checks in the benchmark tests can be removed. Same goes for the performance measurements in the string/test-*.
90 lines
3.3 KiB
Plaintext
90 lines
3.3 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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Benchmark Sets:
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==============
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In addition to standard benchmarking of functions, one may also generate
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custom outputs for a set of functions. This is currently used by string
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function benchmarks where the aim is to compare performance between
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implementations at various alignments and for various sizes.
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To add a benchset for `foo':
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- Add `foo' to the benchset variable.
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- Write your bench-foo.c that prints out the measurements to stdout.
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- On execution, a bench-foo.out is created in $(objpfx) with the contents of
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stdout.
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