2. ISA-L Compression Poll Mode Driver
The ISA-L PMD (librte_pmd_isal_comp) 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).
ISA-L PMD has support for:
Huffman code type:
Window size support:
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|
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.
- Chained mbufs will not be supported until a future release, meaning max data size being passed to PMD through a single mbuf is 64K - 1. If data is larger than this it will need to be split up and sent as multiple operations.
- Compressdev level 0, no compression, is not supported.
- Checksums will not be supported until future release.
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:
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/
In order to enable this virtual compression PMD, user must:
To use the PMD in an application, user must:
rte_vdev_init("compress_isal")within the application.
--vdev="compress_isal"in the EAL options, which will call
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).