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.
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 callrte_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).