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1) Parallel Compression Benchmark
*********************************
1.1) How was the Benchmark Performed?
An optimized build of squashfs-tools-ng was compiled and installed to a tmpfs:
$ mkdir /dev/shm/temp
$ ln -s /dev/shm/temp out
$ ./autogen.sh
$ ./configure CFLAGS="-O3 -Ofast -march=native -mtune=native" \
LDFLAGS="-O3 -Ofast" --prefix=$(pwd)/out
$ make -j install
$ cd out
A SquashFS image to be tested was unpacked in this directory:
$ ./bin/sqfs2tar <IMAGE> > test.tar
And then repacked as follows:
$ time ./bin/tar2sqfs -j <NUM_CPU> -c <COMPRESSOR> -f test.sqfs < test.tar
Out of 4 runs, the worst wall-clock time ("real") was used for comparison.
For the serial reference version, configure was re-run with the option
--without-pthread, the tools re-compiled and re-installed.
1.2) What Image was Tested?
A Debian image extracted from the Debian 10.2 LiveDVD for AMD64 with XFCE
was used.
The input size and resulting output sizes turned out to be as follows:
- As uncompressed tarball: ~6.5GiB (7,008,118,272)
- As LZ4 compressed SquashFS image: ~3.1GiB (3,381,751,808)
- As LZO compressed SquashFS image: ~2.5GiB (2,732,015,616)
- As zstd compressed SquashFS image: ~2.1GiB (2,295,017,472)
- As gzip compressed SquashFS image: ~2.3GiB (2,471,276,544)
- As lzma compressed SquashFS image: ~2.0GiB (2,102,169,600)
- As XZ compressed SquashFS image: ~2.0GiB (2,098,466,816)
The Debian image is expected to contain realistic input data for a Linux
file system and also provide enough data for an interesting benchmark.
1.3) What Test System was used?
AMD Ryzen 7 3700X
32GiB DDR4 RAM
Fedora 31
1.4) What software version was used?
squashfs-tools-ng v0.9
TODO: update data and write the *exact* commit hash here.
1.5) Results
The raw timing results are as follows:
Jobs XZ lzma gzip LZO LZ4 zstd
serial 17m39.613s 16m10.710s 9m56.606s 13m22.337s 12.159s 9m33.600s
1 17m38.050s 15m49.753s 9m46.948s 13m06.705s 11.908s 9m23.445s
2 9m26.712s 8m24.706s 5m08.152s 6m53.872s 7.395s 5m 1.734s
3 6m29.733s 5m47.422s 3m33.235s 4m44.407s 6.069s 3m30.708s
4 5m02.993s 4m30.361s 2m43.447s 3m39.825s 5.864s 2m44.418s
5 4m07.959s 3m40.860s 2m13.454s 2m59.395s 5.749s 2m16.745s
6 3m30.514s 3m07.816s 1m53.641s 2m32.461s 5.926s 1m57.607s
7 3m04.009s 2m43.765s 1m39.742s 2m12.536s 6.281s 1m43.734s
8 2m45.050s 2m26.996s 1m28.776s 1m58.253s 6.395s 1m34.500s
9 2m34.993s 2m18.868s 1m21.668s 1m50.461s 6.890s 1m29.820s
10 2m27.399s 2m11.214s 1m15.461s 1m44.060s 7.225s 1m26.176s
11 2m20.068s 2m04.592s 1m10.286s 1m37.749s 7.557s 1m22.566s
12 2m13.131s 1m58.710s 1m05.957s 1m32.596s 8.127s 1m18.883s
13 2m07.472s 1m53.481s 1m02.041s 1m27.982s 8.704s 1m16.218s
14 2m02.365s 1m48.773s 1m00.337s 1m24.444s 9.494s 1m14.175s
15 1m58.298s 1m45.079s 58.348s 1m21.445s 10.192s 1m12.134s
16 1m55.940s 1m42.176s 56.615s 1m19.030s 10.964s 1m11.049s
The file "benchmark.ods" contains those values, values derived from this and
charts depicting the results.
1.6) Discussion
Most obviously, the results indicate that LZ4, unlike the other compressors,
is clearly I/O bound and not CPU bound and doesn't benefit from parallelization
beyond 2-4 worker threads and even that benefit is marginal with efficiency
plummetting immediately.
The other compressors are clearly CPU bound. Speedup increases linearly until
about 8 cores, but with a slope < 1, as evident by efficiency linearly
decreasing and reaching 80% for 8 cores.
A reason for this sub-linear scaling may be the choke point introduced by the
creation of fragment blocks, that *requires* a synchronization. To test this
theory, a second benchmark should be performed with fragment block generation
completely disabled. This requires a new flag to be added to tar2sqfs (and
also gensquashfs).
Using more than 8 jobs causes a much slower increase in speedup and efficency
declines even faster. This is probably due to the fact that the test system
only has 8 physical cores and beyond that, SMT has to be used.
It should also be noted that the thread pool compressor with only a single
thread turns out to be *slightly* faster than the serial reference
implementation. A possible explanation for this might be that the fragment
blocks are actually assembled in the main thread, in parallel to the worker
that can still continue with other data blocks. Because of this decoupling
there is in fact some degree of parallelism, even if only one worker thread
is used.
As a side effect, this benchmark also produces some insights into the
compression ratio and throughput of the supported compressors. Indicating that
for the Debian live image, XZ clearly provides the highest data density, while
LZ4 is clearly the fastest compressor available.
The throughput of the zstd compressor is comparable to gzip, while the
resulting compression ratio is closer to LZMA.
Repeating the benchmark without tail-end-packing and with fragments completely
disabled would also show the effectiveness of tail-end-packing and fragment
packing as a side effect.
2) Reference Decompression Benchmark
************************************
2.1) How was the Benchmark Performed?
An optimized build of squashfs-tools-ng was compiled and installed to a tmpfs:
$ mkdir /dev/shm/temp
$ ln -s /dev/shm/temp out
$ ./autogen.sh
$ ./configure CFLAGS="-O3 -Ofast -march=native -mtune=native" \
LDFLAGS="-O3 -Ofast" --prefix=$(pwd)/out
$ make -j install
$ cd out
A SquashFS image to be tested was repacked with a desired compressor in
this directory:
$ ./bin/sqfs2tar <IMAGE> | ./bin/tar2sqfs -c <COMPRESSOR> test.sqfs
And then unpacked as follows:
$ time ./bin/sqfs2tar test.sqfs > /dev/null
Out of 4 runs, the worst wall-clock time ("real") was used for comparison.
2.2) What Image was Tested?
A Debian image extracted from the Debian 10.2 LiveDVD for AMD64 with XFCE
was used.
The input size and resulting output sizes turned out to be as follows:
- As LZ4 compressed SquashFS image: ~3.1GiB (3,381,751,808)
- As LZO compressed SquashFS image: ~2.5GiB (2,732,015,616)
- As zstd compressed SquashFS image: ~2.1GiB (2,295,017,472)
- As gzip compressed SquashFS image: ~2.3GiB (2,471,276,544)
- As lzma compressed SquashFS image: ~2.0GiB (2,102,169,600)
- As XZ compressed SquashFS image: ~2.0GiB (2,098,466,816)
- As uncompressed tarball: ~6.5GiB (7,008,118,272)
The Debian image is expected to contain realistic input data for a Linux
file system and also provide enough data for an interesting benchmark.
2.3) What Test System was used?
AMD Ryzen 7 3700X
32GiB DDR4 RAM
Fedora 32
2.4) What software version was used?
squashfs-tools-ng commit cc1141984a03da003e15ff229d3b417f8e5a24ad
2.5) Results
gzip 20.466s
lz4 2.519s
lzma 1m58.455s
lzo 10.521s
xz 1m59.451s
zstd 7.833s
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