ceph/src/seastar/dpdk/doc/guides/compressdevs/isal.rst

   1 ..  SPDX-License-Identifier: BSD-3-Clause
   2     Copyright(c) 2018 Intel Corporation.
   3
   4 ISA-L Compression Poll Mode Driver
   5 ==================================
   6
   7 The ISA-L PMD (**librte_pmd_isal_comp**) provides poll mode compression &
   8 decompression driver support for utilizing Intel ISA-L library,
   9 which implements the deflate algorithm for both Deflate(compression) and Inflate(decompression).
  10
  11
  12 Features
  13 --------
  14
  15 ISA-L PMD has support for:
  16
  17 Compression/Decompression algorithm:
  18
  19     * DEFLATE
  20
  21 Huffman code type:
  22
  23     * FIXED
  24     * DYNAMIC
  25
  26 Window size support:
  27
  28     * 32K
  29
  30 Checksum:
  31
  32     * CRC32
  33     * ADLER32
  34
  35 To enable a checksum in the driver, the compression and/or decompression xform
  36 structure, rte_comp_xform, must be filled with either of the CompressDev
  37 checksum flags supported. ::
  38
  39  compress_xform->compress.chksum = RTE_COMP_CHECKSUM_CRC32
  40
  41  decompress_xform->decompress.chksum = RTE_COMP_CHECKSUM_CRC32
  42
  43 ::
  44
  45  compress_xform->compress.chksum = RTE_COMP_CHECKSUM_ADLER32
  46
  47  decompress_xform->decompress.chksum = RTE_COMP_CHECKSUM_ADLER32
  48
  49 If you request a checksum for compression or decompression,
  50 the checksum field in the operation structure,  ``op->output_chksum``,
  51 will be filled with the checksum.
  52
  53 .. Note::
  54
  55  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.
  56
  57 Level guide:
  58
  59 The ISA-L levels have been mapped to somewhat correspond to the same ZLIB level,
  60 i.e. ZLIB L1 gives a compression ratio similar to ISA-L L1.
  61 Compressdev level 0 enables "No Compression", which passes the uncompressed
  62 data to the output buffer, plus deflate headers.
  63 The ISA-L library does not support this, therefore compressdev level 0 is not supported.
  64
  65 The compressdev API has 10 levels, 0-9. ISA-L has 4 levels of compression, 0-3.
  66 As a result the level mappings from the API to the PMD are shown below.
  67
  68 .. _table_ISA-L_compression_levels:
  69
  70 .. table:: Level mapping from Compressdev to ISA-L PMD.
  71
  72    +-------------+----------------------------------------------+-----------------------------------------------+
  73    | Compressdev | PMD Functionality                            | Internal ISA-L                                |
  74    | API Level   |                                              | Level                                         |
  75    +=============+==============================================+===============================================+
  76    | 0           | No compression, Not Supported                | ---                                           |
  77    +-------------+----------------------------------------------+-----------------------------------------------+
  78    | 1           | Dynamic (Fast compression)                   | 1                                             |
  79    +-------------+----------------------------------------------+-----------------------------------------------+
  80    | 2           | Dynamic                                      | 2                                             |
  81    |             | (Higher compression ratio)                   |                                               |
  82    +-------------+----------------------------------------------+-----------------------------------------------+
  83    | 3           | Dynamic                                      | 3                                             |
  84    |             | (Best compression ratio)                     | (Level 2 if                                   |
  85    |             |                                              | no AVX512/AVX2)                               |
  86    +-------------+----------------------------------------------+-----------------------------------------------+
  87    | 4           | Dynamic (Best compression ratio)             | Same as above                                 |
  88    +-------------+----------------------------------------------+-----------------------------------------------+
  89    | 5           | Dynamic (Best compression ratio)             | Same as above                                 |
  90    +-------------+----------------------------------------------+-----------------------------------------------+
  91    | 6           | Dynamic (Best compression ratio)             | Same as above                                 |
  92    +-------------+----------------------------------------------+-----------------------------------------------+
  93    | 7           | Dynamic (Best compression ratio)             | Same as above                                 |
  94    +-------------+----------------------------------------------+-----------------------------------------------+
  95    | 8           | Dynamic (Best compression ratio)             | Same as above                                 |
  96    +-------------+----------------------------------------------+-----------------------------------------------+
  97    | 9           | Dynamic (Best compression ratio)             | Same as above                                 |
  98    +-------------+----------------------------------------------+-----------------------------------------------+
  99
 100 .. Note::
 101
 102  The above table only shows mapping when API calls for dynamic compression.
 103  For fixed compression, regardless of API level, internally ISA-L level 0 is always used.
 104
 105
 106 Limitations
 107 -----------
 108
 109 * Compressdev level 0, no compression, is not supported.
 110
 111 Installation
 112 ------------
 113
 114 * To build DPDK with Intel's ISA-L library, the user is required to download the library from `<https://github.com/01org/isa-l>`_.
 115
 116 * Once downloaded, the user needs to build the library, the ISA-L autotools are usually sufficient::
 117
 118     ./autogen.sh
 119     ./configure
 120
 121 * make can  be used to install the library on their system, before building DPDK::
 122
 123     make
 124     sudo make install
 125
 126 * To build with meson, the **libisal.pc** file, must be copied into "pkgconfig",
 127   e.g. /usr/lib/pkgconfig or /usr/lib64/pkgconfig depending on your system,
 128   for meson to find the ISA-L library. The **libisal.pc** is located in library sources::
 129
 130     cp isal/libisal.pc /usr/lib/pkgconfig/
 131
 132
 133 Initialization
 134 --------------
 135
 136 In order to enable this virtual compression PMD, user must:
 137
 138 * Set ``CONFIG_RTE_LIBRTE_PMD_ISAL=y`` in config/common_base.
 139
 140 To use the PMD in an application, user must:
 141
 142 * Call ``rte_vdev_init("compress_isal")`` within the application.
 143
 144 * Use ``--vdev="compress_isal"`` in the EAL options, which will call ``rte_vdev_init()`` internally.
 145
 146 The following parameter (optional) can be provided in the previous two calls:
 147
 148 * ``socket_id:`` Specify the socket where the memory for the device is going to be allocated
 149   (by default, socket_id will be the socket where the core that is creating the PMD is running on).