From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 0BDB843C8A; Mon, 11 Mar 2024 21:32:09 +0100 (CET) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 8075140EF0; Mon, 11 Mar 2024 21:31:44 +0100 (CET) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mails.dpdk.org (Postfix) with ESMTP id 64DB640647 for ; Mon, 11 Mar 2024 21:31:38 +0100 (CET) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BB06D153B; Mon, 11 Mar 2024 13:32:14 -0700 (PDT) Received: from ampere-altra-2-1.usa.Arm.com (ampere-altra-2-1.usa.arm.com [10.118.91.158]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A54A33F73F; Mon, 11 Mar 2024 13:31:37 -0700 (PDT) From: Paul Szczepanek To: dev@dpdk.org Cc: bruce.richardson@intel.com, Paul Szczepanek , Honnappa Nagarahalli , Nathan Brown Subject: [PATCH v10 4/5] docs: add pointer compression guide Date: Mon, 11 Mar 2024 20:31:28 +0000 Message-Id: <20240311203129.335720-5-paul.szczepanek@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240311203129.335720-1-paul.szczepanek@arm.com> References: <20230927150854.3670391-2-paul.szczepanek@arm.com> <20240311203129.335720-1-paul.szczepanek@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Documentation added in the prog guide for the new utility functions for pointer compression showing example code and potential usecases. Signed-off-by: Paul Szczepanek Reviewed-by: Honnappa Nagarahalli Reviewed-by: Nathan Brown --- MAINTAINERS | 1 + doc/guides/prog_guide/index.rst | 1 + doc/guides/prog_guide/ptr_compress_lib.rst | 142 +++++++++++++++++++++ 3 files changed, 144 insertions(+) create mode 100644 doc/guides/prog_guide/ptr_compress_lib.rst diff --git a/MAINTAINERS b/MAINTAINERS index 6f703b1b13..e70f92cdc4 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -1688,6 +1688,7 @@ F: lib/pci/ Pointer Compression M: Paul Szczepanek F: lib/ptr_compress/ +F: doc/guides/prog_guide/ptr_compress_lib.rst Power management M: Anatoly Burakov diff --git a/doc/guides/prog_guide/index.rst b/doc/guides/prog_guide/index.rst index d09d958e6c..6366849eb0 100644 --- a/doc/guides/prog_guide/index.rst +++ b/doc/guides/prog_guide/index.rst @@ -73,6 +73,7 @@ Programmer's Guide telemetry_lib bpf_lib graph_lib + ptr_compress_lib build-sdk-meson meson_ut build_app diff --git a/doc/guides/prog_guide/ptr_compress_lib.rst b/doc/guides/prog_guide/ptr_compress_lib.rst new file mode 100644 index 0000000000..1f9ef24da7 --- /dev/null +++ b/doc/guides/prog_guide/ptr_compress_lib.rst @@ -0,0 +1,142 @@ +.. SPDX-License-Identifier: BSD-3-Clause + Copyright(c) 2024 Arm Limited. + +Pointer Compression Library +=========================== + +Use ``rte_ptr_compress_16()`` and ``rte_ptr_decompress_16()`` to compress and +decompress pointers into 16-bit offsets. Use ``rte_ptr_compress_32()`` and +``rte_ptr_decompress_32()`` to compress and decompress pointers into 32-bit +offsets. + +Compression takes advantage of the fact that pointers are usually located in a +limited memory region (like a mempool). By converting them to offsets from a +base memory address they can be stored in fewer bytes. How many bytes are needed +to store the offset is dictated by the memory region size and alignment of +objects the pointers point to. + +For example, a pointer which is part of a 4GB memory pool can be stored as 32 +bit offset. If the pointer points to memory that is 8 bytes aligned then 3 bits +can be dropped from the offset and a 32GB memory pool can now fit in 32 bits. + +For performance reasons these requirements are not enforced programmatically. +The programmer is responsible for ensuring that the combination of distance +from the base pointer and memory alignment allow for storing of the offset in +the number of bits indicated by the function name (16 or 32). Start of mempool +memory would be a good candidate for the base pointer. Otherwise any pointer +that precedes all pointers, is close enough and has the same alignment as the +pointers being compressed will work. + +.. note:: + + Performance gains depend on the batch size of pointers and CPU capabilities + such as vector extensions. It's important to measure the performance + increase on target hardware. A test called ``ring_perf_autotest`` in + ``dpdk-test`` can provide the measurements. + +Example usage +~~~~~~~~~~~~~ + +In this example we send pointers between two cores through a ring. While this +is a realistic use case the code is simplified for demonstration purposes and +does not have error handling. + +.. code-block:: c + + #include + #include + #include + #include + + #define ITEMS_ARRAY_SIZE (1024) + #define BATCH_SIZE (128) + #define ALIGN_EXPONENT (3) + #define ITEM_ALIGN (1<