Fuzzer: Adjust parameters by input size, sometimes #7276
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tlively
reviewed
Feb 7, 2025
| // A typical random wasm input from fuzz_opt.py is fairly large (to minimize | ||
| // the process creation overhead of all the things we run from python), and | ||
| // the defaults are tuned to that. | ||
| double size = random.remaining(); |
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Why does random.remaining() correspond to the input size? This seems non-obvious, so perhaps is worth a comment.
| // the process creation overhead of all the things we run from python), and | ||
| // the defaults are tuned to that. | ||
| double size = random.remaining(); | ||
| const double MEAN_SIZE = 40 * 1024; |
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Is this number taken from measurements? Do we expect it to change much over time? (Not that it would matter much if it did.)
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| auto bits = random.get(); | ||
| if (bits & 1) { | ||
| fuzzParams->MAX_NEW_GC_TYPES = fuzzParams->MAX_NEW_GC_TYPES * ratio; |
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Can we use *= ratio here and below?
| // Only increase the number of tries. Trying fewer times does not help | ||
| // find more interesting patterns. | ||
| if (ratio > 1) { | ||
| fuzzParams->TRIES = fuzzParams->TRIES * ratio; |
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Can we give TRIES a more descriptive name?
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Rather than always have a fixed max of heap types, globals, etc. allow more if the
input size is large. This adds variety.
There is a cost to this variety, we go from 0.89% ignored runs to 1.1% (that is,
slightly more runs contain something that prevents us from doing the work
we want, like hitting a host limitation or seeing the testcase just traps). This
increase seems small enough to be reasonable, and we only do this half the
time, so the old behavior is still being tested at half throughput.