From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id C31D3A04B5; Wed, 30 Sep 2020 15:09:09 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id F3F771DAE6; Wed, 30 Sep 2020 15:08:16 +0200 (CEST) Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by dpdk.org (Postfix) with ESMTP id 41B321D630 for ; Wed, 30 Sep 2020 15:08:10 +0200 (CEST) IronPort-SDR: 9QJImaHHn9+KVhQInaxZ9pDc6tzvZc0blhT45gLdnkkauVLwo8UREckQZlv51hMxOxKduG8mKc eRtqO/oKYfNw== X-IronPort-AV: E=McAfee;i="6000,8403,9759"; a="150223448" X-IronPort-AV: E=Sophos;i="5.77,322,1596524400"; d="scan'208";a="150223448" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Sep 2020 06:08:08 -0700 IronPort-SDR: zbFH8STS1FMRP2BhXjjCSAI4k+uSU2D0HjdXUEGRv6RmxR1Hu29VhCUp35UEg3kFM0dpGo3eXA 6heWBX15n97g== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.77,322,1596524400"; d="scan'208";a="294603183" Received: from silpixa00399953.ir.intel.com (HELO silpixa00399953.ger.corp.intel.com) ([10.237.222.53]) by fmsmga008.fm.intel.com with ESMTP; 30 Sep 2020 06:08:06 -0700 From: Ciara Power To: dev@dpdk.org Cc: Ciara Power , Anatoly Burakov , John McNamara , Marko Kovacevic Date: Wed, 30 Sep 2020 14:03:59 +0100 Message-Id: <20200930130415.11211-4-ciara.power@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200930130415.11211-1-ciara.power@intel.com> References: <20200807155859.63888-1-ciara.power@intel.com> <20200930130415.11211-1-ciara.power@intel.com> Subject: [dpdk-dev] [PATCH v3 03/18] doc: add detail on using max SIMD bitwidth X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" This patch adds documentation on the usage of the max SIMD bitwidth EAL setting, and how to use it to enable AVX-512 at runtime. Cc: Anatoly Burakov Cc: John McNamara Cc: Marko Kovacevic Signed-off-by: Ciara Power --- v3: - Added enum value for disabling use of max SIMD to doc. - Added entry to HowTo index. --- doc/guides/howto/avx512.rst | 36 +++++++++++++++++++ doc/guides/howto/index.rst | 1 + doc/guides/linux_gsg/eal_args.include.rst | 16 +++++++++ .../prog_guide/env_abstraction_layer.rst | 32 +++++++++++++++++ 4 files changed, 85 insertions(+) create mode 100644 doc/guides/howto/avx512.rst diff --git a/doc/guides/howto/avx512.rst b/doc/guides/howto/avx512.rst new file mode 100644 index 0000000000..ebae0f2b4f --- /dev/null +++ b/doc/guides/howto/avx512.rst @@ -0,0 +1,36 @@ +.. SPDX-License-Identifier: BSD-3-Clause + Copyright(c) 2020 Intel Corporation. + + +Using AVX-512 with DPDK +======================= + +AVX-512 is not used by default in DPDK, but it can be selected at runtime by apps through the use of EAL API, +and by the user with a commandline argument. DPDK has a setting for max SIMD bitwidth, +which can be modified and will then limit the vector path taken by the code. + + +Using the API in apps +--------------------- + +Apps can request DPDK uses AVX-512 at runtime, if it provides improved application performance. +This can be done by modifying the EAL setting for max SIMD bitwidth to 512, as by default it is 256, +which does not allow for AVX-512. + +.. code-block:: c + + rte_set_max_simd_bitwidth(RTE_MAX_512_SIMD); + +This API should only be called once at initialization, before EAL init. +For more information on the possible enum values to use as a parameter, go to :ref:`max_simd_bitwidth`: + + +Using the command-line argument +--------------------------------------------- + +The user can select to use AVX-512 at runtime, using the following argument to set the max bitwidth:: + + ./app/dpdk-testpmd --force-max-simd-bitwidth=512 + +This will override any further changes to the max SIMD bitwidth in DPDK, +which is useful for testing purposes. diff --git a/doc/guides/howto/index.rst b/doc/guides/howto/index.rst index 5a97ea508c..c2a2c60ddb 100644 --- a/doc/guides/howto/index.rst +++ b/doc/guides/howto/index.rst @@ -20,3 +20,4 @@ HowTo Guides telemetry debug_troubleshoot openwrt + avx512 diff --git a/doc/guides/linux_gsg/eal_args.include.rst b/doc/guides/linux_gsg/eal_args.include.rst index 0fe4457968..a0bfbd1a98 100644 --- a/doc/guides/linux_gsg/eal_args.include.rst +++ b/doc/guides/linux_gsg/eal_args.include.rst @@ -210,3 +210,19 @@ Other options * ``--no-telemetry``: Disable telemetry. + +* ``--force-max-simd-bitwidth=``: + + Specify the maximum SIMD bitwidth size to handle. This limits which vector paths, + if any, are taken, as any paths taken must use a bitwidth below the max bitwidth limit. + For example, to allow all SIMD bitwidths up to and including AVX-512:: + + --force-max-simd-bitwidth=512 + + The following example shows limiting the bitwidth to 64-bits to disable all vector code:: + + --force-max-simd-bitwidth=64 + + To disable use of max SIMD bitwidth limit:: + + --force-max-simd-bitwidth=0 diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst index f64ae953d1..58f591e921 100644 --- a/doc/guides/prog_guide/env_abstraction_layer.rst +++ b/doc/guides/prog_guide/env_abstraction_layer.rst @@ -486,6 +486,38 @@ the desired addressing mode when virtual devices that are not directly attached To facilitate forcing the IOVA mode to a specific value the EAL command line option ``--iova-mode`` can be used to select either physical addressing('pa') or virtual addressing('va'). +.. _max_simd_bitwidth: + + +Max SIMD bitwidth +~~~~~~~~~~~~~~~~~ + +The EAL provides a single setting to limit the max SIMD bitwidth used by DPDK, +which is used in determining the vector path, if any, chosen by a component. +The value can be set at runtime by an application using the 'rte_set_max_simd_bitwidth(uint16_t bitwidth)' function, +which should only be called once at initialization, before EAL init. +The value can be overridden by the user using the EAL command-line option '--force-max-simd-bitwidth'. + +When choosing a vector path, along with checking the CPU feature support, +the value of the max SIMD bitwidth must also be checked, and can be retrieved using the 'rte_get_max_simd_bitwidth()' function. +The value should be compared against the enum values for accepted max SIMD bitwidths: + +.. code-block:: c + + enum rte_max_simd_t { + RTE_NO_SIMD = 64, + RTE_MAX_128_SIMD = 128, + RTE_MAX_256_SIMD = 256, + RTE_MAX_512_SIMD = 512, + RTE_MAX_SIMD_DISABLE = UINT16_MAX, + }; + + if (rte_get_max_simd_bitwidth() >= RTE_MAX_512_SIMD) + /* Take AVX-512 vector path */ + else if (rte_get_max_simd_bitwidth() >= RTE_MAX_256_SIMD) + /* Take AVX2 vector path */ + + Memory Segments and Memory Zones (memzone) ------------------------------------------ -- 2.17.1