2. ISA-L Compression Poll Mode Driver

The ISA-L PMD (librte_compress_isal) provides poll mode compression & decompression driver support for utilizing Intel ISA-L library, which implements the deflate algorithm for both Deflate(compression) and Inflate(decompression).

2.1. Features

ISA-L PMD has support for:

Compression/Decompression algorithm:

  • DEFLATE

Huffman code type:

  • FIXED
  • DYNAMIC

Window size support:

  • 32K

Checksum:

  • CRC32
  • ADLER32

To enable a checksum in the driver, the compression and/or decompression xform structure, rte_comp_xform, must be filled with either of the CompressDev checksum flags supported.

compress_xform->compress.chksum = RTE_COMP_CHECKSUM_CRC32

decompress_xform->decompress.chksum = RTE_COMP_CHECKSUM_CRC32

compress_xform->compress.chksum = RTE_COMP_CHECKSUM_ADLER32

decompress_xform->decompress.chksum = RTE_COMP_CHECKSUM_ADLER32

If you request a checksum for compression or decompression, the checksum field in the operation structure, op->output_chksum, will be filled with the checksum.

Note

For the compression case above, your output buffer will need to be large enough to hold the compressed data plus a scratchpad for the checksum at the end, the scratchpad is 8 bytes for CRC32 and 4 bytes for Adler32.

Level guide:

The ISA-L levels have been mapped to somewhat correspond to the same ZLIB level, i.e. ZLIB L1 gives a compression ratio similar to ISA-L L1. Compressdev level 0 enables “No Compression”, which passes the uncompressed data to the output buffer, plus deflate headers. The ISA-L library does not support this, therefore compressdev level 0 is not supported.

The compressdev API has 10 levels, 0-9. ISA-L has 4 levels of compression, 0-3. As a result the level mappings from the API to the PMD are shown below.

Table 2.2 Level mapping from Compressdev to ISA-L PMD.
Compressdev API Level PMD Functionality Internal ISA-L Level
0 No compression, Not Supported —
1 Dynamic (Fast compression) 1
2 Dynamic (Higher compression ratio) 2
3 Dynamic (Best compression ratio) 3 (Level 2 if no AVX512/AVX2)
4 Dynamic (Best compression ratio) Same as above
5 Dynamic (Best compression ratio) Same as above
6 Dynamic (Best compression ratio) Same as above
7 Dynamic (Best compression ratio) Same as above
8 Dynamic (Best compression ratio) Same as above
9 Dynamic (Best compression ratio) Same as above

Note

The above table only shows mapping when API calls for dynamic compression. For fixed compression, regardless of API level, internally ISA-L level 0 is always used.

2.2. Limitations

  • Compressdev level 0, no compression, is not supported.

2.3. Installation

  • To build DPDK with Intel’s ISA-L library, the user is required to download the library from https://github.com/01org/isa-l.

  • Once downloaded, the user needs to build the library, the ISA-L autotools are usually sufficient:

    ./autogen.sh
./configure

  • make can be used to install the library on their system, before building DPDK:

    make
sudo make install

  • To build with meson, the libisal.pc file, must be copied into “pkgconfig”, e.g. /usr/lib/pkgconfig or /usr/lib64/pkgconfig depending on your system, for meson to find the ISA-L library. The libisal.pc is located in library sources:

    cp isal/libisal.pc /usr/lib/pkgconfig/

2.4. Initialization

To use the PMD in an application, user must:

  • Call rte_vdev_init("compress_isal") within the application.
  • Use --vdev="compress_isal" in the EAL options, which will call rte_vdev_init() internally.

The following parameter (optional) can be provided in the previous two calls:

  • socket_id: Specify the socket where the memory for the device is going to be allocated (by default, socket_id will be the socket where the core that is creating the PMD is running on).