657.xz_s
Lasse Collin <lasse.collin [at] tukaani.org> is the author of XZ Utils
Igor Pavlov wrote key portions of the compression algorithm, according to the references.
Jindrich Novy wrote pxz, which is used by the SPEC version to provide parallelism when multiple OpenMP threads are available.
Data compression
657.xz_s is based directly on Lasse Collin's XZ Utils 5.0.5, with these differences: it incorporates pxz; performs no file I/O other than reading the input; does all compression and decompression entirely in memory; and prefers generic portable routines rather than platform-specific routines. As usual for SPEC CPU®, the intent is to measure the compute-intensive portion of a real application, while minimizing IO; thereby focusing on the performance of the CPU, memory, and compiler.
Inputs for 657.xz_s are XZ-compressed files containing the data that will be compressed during the test. The reference (timed) workloads use three components: a tar archive of HTML documentation and some supporting images; a database of ClamAV malware signatures; and an input file with combined text and image data. All three have highly compressible sections and incompressible sections.
Parameters for each test are taken from the command line. In order, they are:
| The refrate workload (for 557.xz_r) is invoked with these parameters: | ||||
| Input file | Buffer (MiB) | Minimum | Maximum | Compression level |
|---|---|---|---|---|
| cld.tar.xz | 160 | 59,796,407 | 61,004,416 | 6 |
| cpu2006docs.tar.xz | 250 | 23,047,774 | 23,513,385 | 6e |
| input.combined.xz | 250 | 40,401,484 | 41,217,675 | 7 |
| The refspeed workload (for 657.xz_s) uses: | ||||
| Input file | Buffer (MiB) | Minimum | Maximum | Compression level |
| cpu2006docs.tar.xz | 6643 | 1,036,078,272 | 1,111,795,472 | 4 |
| cld.tar.xz | 1400 | 536,995,164 | 539,938,872 | 8 |
Command lines are constructed by the run harness from the contents of the control file. Adding new workloads is quite simple; it's just a file of data to be compressed and an entry for that file in the control file.
Each input set is initially decompressed and the SHA-512 sum of the decompression is verified against the one specified on the command line. Then that input is duplicated (or truncated) until its size matches what was requested on the command line. It's then compressed using the XZ preset ("compression level") requested on the command line. Verification of compressed size is output, if compressed size checking is enabled. (Compressed data size may vary slightly depending on the number of threads used to do compression.) That compressed data is then decompressed and its SHA-512 sum calculated and compared to the one generated during the initial load. Doing the comparison in this way reduces the verification-related memory access for the benchmark, as well as its memory footprint.
About memory usage: The second parameter selects the size of a buffer that will be the input to the compression phase. The total virtual memory used by the benchmark will be larger. On one particular platform tested by SPEC, the total memory for 557.xz_r and 657.xz_s was about
(2 * the buffer size) + (0.5 to 1.0 GiB)
Your usage may vary, depending on (among other things): compiler options, operating system, and the number of OpenMP threads.
The output files provide a brief outline of what the benchmark is doing as it runs. Output sizes for each compression and decompression are printed to facilitate validation, and the results of decompression are compared with the input data to ensure that they match.
ISO C99
OpenMP for speed workload
None
The benchmark is based on XZ Utils 5.0.5, which is Public Domain. It includes a modified version of Jindrich Novy's pxz, which is licensed under GPLv2 or later. SPEC started from pxz revision ae80846 from 18 October 2014. Additional components added by SPEC are mentioned at SPEC CPU®2017 Licenses.
Last updated: $Date: 2020-08-19 18:52:31 -0400 (Wed, 19 Aug 2020) $
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