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We were compressing unitialized memory, which should not result in
any problems, but is inelegant.
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If both lz4 and xz are enabled, this results in a limit of
2×3×2 s ~= 12 s runtime.
Previous implementation started with really small buffer sizes. When
combined with a short time limit this resulteded in abysmal results for xz.
It seems that the initialization overead is really significant for small
buffers. Since xz will not be used by default anymore, this does not
seem worth fixing. Instead buffer sizes are changed to run a
pseudo-random non-repeating pattern. This should allow reasonable testing
for all buffer sizes. For testing, both runtime and the buffer size seed
can be specified on the command line. Sufficiently large runtime allows
all buffer sizes up to 1MB to be tested.
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Existing test would use highly-compressible repeatable
input. Two types of input are added:
- zeros
- random blocks interspersed with zeros
The idea is to get more information about behaviour in various cases.
On Intel Xeon the results are:
% ./test-compress-benchmark
XZ/zeros: compressed & decompressed 2535301373 bytes in 32.56s (74.26MiB/s), mean compresion 99.96%, skipped 3160 bytes
LZ4/zeros: compressed & decompressed 2535304362 bytes in 1.16s (2088.69MiB/s), mean compresion 99.60%, skipped 171 bytes
XZ/simple: compressed & decompressed 2535300963 bytes in 30.42s (79.48MiB/s), mean compresion 99.95%, skipped 3570 bytes
LZ4/simple: compressed & decompressed 2535303543 bytes in 1.22s (1978.86MiB/s), mean compresion 99.60%, skipped 990 bytes
XZ/random: compressed & decompressed 381756649 bytes in 60.02s (6.07MiB/s), mean compresion 39.64%, skipped 27813723 bytes
LZ4/random: compressed & decompressed 2507385036 bytes in 0.97s (2477.52MiB/s), mean compresion 54.77%, skipped 27919497 bytes
If someone has ideas for more realistic test cases, they can be easily
added to this framework.
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Otherwise they can be optimized away with -DNDEBUG
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They have different size on 32 bit, so they are really not interchangable.
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and btw make it pass for 32bits where size_t != uint64_t
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This is useful to test the behaviour of the compressor for various buffer
sizes.
Time is limited to a minute per compression, since otherwise, when LZ4
takes more than a second which is necessary to reduce the noise, XZ
takes more than 10 minutes.
% build/test-compress-benchmark (without time limit)
XZ: compressed & decompressed 2535300963 bytes in 794.57s (3.04MiB/s), mean compresion 99.95%, skipped 3570 bytes
LZ4: compressed & decompressed 2535303543 bytes in 1.56s (1550.07MiB/s), mean compresion 99.60%, skipped 990 bytes
% build/test-compress-benchmark (with time limit)
XZ: compressed & decompressed 174321481 bytes in 60.02s (2.77MiB/s), mean compresion 99.76%, skipped 3570 bytes
LZ4: compressed & decompressed 2535303543 bytes in 1.63s (1480.83MiB/s), mean compresion 99.60%, skipped 990 bytes
It appears that there's a bug in lzma_end where it leaks 32 bytes.
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