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diff --git a/doc/parallelism.txt b/doc/parallelism.txt index 046c559..97bb87e 100644 --- a/doc/parallelism.txt +++ b/doc/parallelism.txt @@ -112,34 +112,129 @@ 2) Benchmarks ************* - TODO: benchmarks with the following images: - - Debian live iso (2G) - - Arch Linux live iso (~550M) - - Raspberry Pi 3 QT demo image (~390M) + 2.1) How was the Benchmark Performed? - sqfs2tar $IMAGE | tar2sqfs -j $NUM_CPU -f out.sqfs + An optimized build of squashfs-tools-ng was compiled and installed to a tmpfs: - Values to measure: - - Total wall clock time of tar2sqfs. - - Througput (bytes read / time, bytes written / time). + $ 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 - Try the above for different compressors and stuff everything into - a huge spread sheet. Then, determine the following and plot some - nice graphs: + A SquashFS image to be tested was unpacked in this directory: - - Absolute speedup (normalized to serial implementation). - - Absolute efficiency (= speedup / $NUM_CPU) - - Relative speedup (normalized to thread pool with -j 1). - - Relative efficiency + $ ./bin/sqfs2tar <IMAGE> > test.tar + And then repacked as follows: - Available test hardware: - - 8(16) core AMD Ryzen 7 3700X, 32GiB DDR4 RAM. - - Various 4 core Intel Xeon servers. Precise Specs not known yet. - - TODO: Check if my credentials on LCC2 still work. The cluster nodes AFAIK - have dual socket Xeons. Not sure if 8 cores per CPU or 8 in total? + $ time ./bin/tar2sqfs -j <NUM_CPU> -c <COMPRESSOR> -f test.sqfs < test.tar - For some compressors and work load, tar2sqfs may be I/O bound rather than CPU - bound. The different machines have different storage which may impact the - result. Should this be taken into account for comparison or eliminated by - using a ramdisk or fiddling with the queue backlog? + + 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. + + + 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 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: ~2.4GiB (2,536,910,848) + - 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. + + + 2.3) What Test System was used? + + AMD Ryzen 7 3700X + 32GiB DDR4 RAM + Fedora 31 with Linux 5.4.17 + + + 2.4) Results + + The raw timing results are as follows: + + Jobs XZ lzma gzip LZO LZ4 zstd + serial 17m59.413s 16m08.868s 10m02.632s 13m17.956s 18.218s 35.280s + 1 18m01.695s 16m02.329s 9m57.334s 13m14.374s 16.727s 34.108s + 2 9m34.939s 8m32.806s 5m12.791s 6m56.017s 13.161s 21.696s + 3 6m37.701s 5m55.246s 3m35.409s 4m50.138s 12.798s 18.265s + 4 5m07.896s 4m34.419s 2m47.108s 3m43.153s 13.191s 16.885s + 5 4m11.593s 3m44.764s 2m17.371s 3m02.429s 14.251s 17.389s + 6 3m34.115s 3m12.032s 1m57.972s 2m35.601s 14.824s 17.023s + 7 3m07.806s 2m47.815s 1m44.661s 2m16.289s 15.643s 17.676s + 8 2m47.589s 2m30.433s 1m33.865s 2m01.389s 16.262s 17.524s + 9 2m38.737s 2m22.159s 1m27.477s 1m53.976s 16.887s 18.110s + 10 2m30.942s 2m14.427s 1m22.424s 1m47.411s 17.316s 18.497s + 11 2m23.512s 2m08.470s 1m17.419s 1m41.965s 17.759s 18.831s + 12 2m17.083s 2m02.814s 1m13.644s 1m36.742s 18.335s 19.082s + 13 2m11.450s 1m57.820s 1m10.310s 1m32.492s 18.827s 19.232s + 14 2m06.525s 1m53.951s 1m07.483s 1m28.779s 19.471s 20.070s + 15 2m02.338s 1m50.358s 1m04.954s 1m25.993s 19.772s 20.608s + 16 1m58.566s 1m47.371s 1m03.616s 1m23.241s 20.188s 21.779s + + The file "benchmark.ods" contains those values, values derived from this and + charts depicting the results. + + + 2.5) Discussion + + Most obviously, the results indicate that LZ4 and zstd compression are clearly + I/O bound and not CPU bound. They don't benefit from parallelization beyond + 2-4 worker threads and even that benefit is marginal with efficiency + plummetting immediately. + + + The other compressors (XZ, lzma, gzip, lzo) are clearly CPU bound. Speedup + increases linearly until about 8 cores, but with a factor k < 1, paralleled by + efficiency decreasing down to 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, directly followed by zstd + which has a much better compression ratio than LZ4, comparable to the gzip + compressor, while being almost 50 times faster. The throughput of the zstd + compressor is truly impressive, considering the compression ratio it achieves. + + Repeating the benchmark without tail-end-packing and wit fragments completely + disabled would also show the effectiveness of tail-end-packing and fragment + packing as a side effect. |