--- /dev/null
+.. BSD LICENSE
+ Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions
+ are met:
+
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in
+ the documentation and/or other materials provided with the
+ distribution.
+ * Neither the name of Intel Corporation nor the names of its
+ contributors may be used to endorse or promote products derived
+ from this software without specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+IVSHMEM Library
+===============
+
+The DPDK IVSHMEM library facilitates fast zero-copy data sharing among virtual machines
+(host-to-guest or guest-to-guest) by means of QEMU's IVSHMEM mechanism.
+
+The library works by providing a command line for QEMU to map several hugepages into a single IVSHMEM device.
+For the guest to know what is inside any given IVSHMEM device
+(and to distinguish between DPDK and non-DPDK IVSHMEM devices),
+a metadata file is also mapped into the IVSHMEM segment.
+No work needs to be done by the guest application to map IVSHMEM devices into memory;
+they are automatically recognized by the DPDK Environment Abstraction Layer (EAL).
+
+A typical DPDK IVSHMEM use case looks like the following.
+
+
+.. figure:: img/ivshmem.*
+
+ Typical Ivshmem use case
+
+
+The same could work with several virtual machines, providing host-to-VM or VM-to-VM communication.
+The maximum number of metadata files is 32 (by default) and each metadata file can contain different (or even the same) hugepages.
+The only constraint is that each VM has to have access to the memory it is sharing with other entities (be it host or another VM).
+For example, if the user wants to share the same memzone across two VMs, each VM must have that memzone in its metadata file.
+
+IVHSHMEM Library API Overview
+-----------------------------
+
+The following is a simple guide to using the IVSHMEM Library API:
+
+* Call rte_ivshmem_metadata_create() to create a new metadata file.
+ The metadata name is used to distinguish between multiple metadata files.
+
+* Populate each metadata file with DPDK data structures.
+ This can be done using the following API calls:
+
+ * rte_ivhshmem_metadata_add_memzone() to add rte_memzone to metadata file
+
+ * rte_ivshmem_metadata_add_ring() to add rte_ring to metadata file
+
+ * rte_ivshmem_metadata_add_mempool() to add rte_mempool to metadata file
+
+* Finally, call rte_ivshmem_metadata_cmdline_generate() to generate the command line for QEMU.
+ Multiple metadata files (and thus multiple command lines) can be supplied to a single VM.
+
+.. note::
+
+ Only data structures fully residing in DPDK hugepage memory work correctly.
+ Supported data structures created by malloc(), mmap()
+ or otherwise using non-DPDK memory cause undefined behavior and even a segmentation fault.
+
+IVSHMEM Environment Configuration
+---------------------------------
+
+The steps needed to successfully run IVSHMEM applications are the following:
+
+* Compile a special version of QEMU from sources.
+
+ The source code can be found on the QEMU website (currently, version 1.4.x is supported, but version 1.5.x is known to work also),
+ however, the source code will need to be patched to support using regular files as the IVSHMEM memory backend.
+ The patch is not included in the DPDK package,
+ but is available on the `Intel®DPDK-vswitch project webpage <https://01.org/packet-processing/intel%C2%AE-ovdk>`_
+ (either separately or in a DPDK vSwitch package).
+
+* Enable IVSHMEM library in the DPDK build configuration.
+
+ In the default configuration, IVSHMEM library is not compiled. To compile the IVSHMEM library,
+ one has to either use one of the provided IVSHMEM targets
+ (for example, x86_64-ivshmem-linuxapp-gcc),
+ or set CONFIG_RTE_LIBRTE_IVSHMEM to "y" in the build configuration.
+
+* Set up hugepage memory on the virtual machine.
+
+ The guest applications run as regular DPDK (primary) processes and thus need their own hugepage memory set up inside the VM.
+ The process is identical to the one described in the *DPDK Getting Started Guide*.
+
+Best Practices for Writing IVSHMEM Applications
+-----------------------------------------------
+
+When considering the use of IVSHMEM for sharing memory, security implications need to be carefully evaluated.
+IVSHMEM is not suitable for untrusted guests, as IVSHMEM is essentially a window into the host process memory.
+This also has implications for the multiple VM scenarios.
+While the IVSHMEM library tries to share as little memory as possible,
+it is quite probable that data designated for one VM might also be present in an IVSMHMEM device designated for another VM.
+Consequently, any shared memory corruption will affect both host and all VMs sharing that particular memory.
+
+IVSHMEM applications essentially behave like multi-process applications,
+so it is important to implement access serialization to data and thread safety.
+DPDK ring structures are already thread-safe, however,
+any custom data structures that the user might need would have to be thread-safe also.
+
+Similar to regular DPDK multi-process applications,
+it is not recommended to use function pointers as functions might have different memory addresses in different processes.
+
+It is best to avoid freeing the rte_mbuf structure on a different machine from where it was allocated,
+that is, if the mbuf was allocated on the host, the host should free it.
+Consequently, any packet transmission and reception should also happen on the same machine (whether virtual or physical).
+Failing to do so may lead to data corruption in the mempool cache.
+
+Despite the IVSHMEM mechanism being zero-copy and having good performance,
+it is still desirable to do processing in batches and follow other procedures described in
+:ref:`Performance Optimization <Performance_Optimization>`.
+
+Best Practices for Running IVSHMEM Applications
+-----------------------------------------------
+
+For performance reasons,
+it is best to pin host processes and QEMU processes to different cores so that they do not interfere with each other.
+If NUMA support is enabled, it is also desirable to keep host process' hugepage memory and QEMU process on the same NUMA node.
+
+For the best performance across all NUMA nodes, each QEMU core should be pinned to host CPU core on the appropriate NUMA node.
+QEMU's virtual NUMA nodes should also be set up to correspond to physical NUMA nodes.
+More on how to set up DPDK and QEMU NUMA support can be found in *DPDK Getting Started Guide* and
+`QEMU documentation <http://qemu.weilnetz.de/qemu-doc.html>`_ respectively.
+A script called cpu_layout.py is provided with the DPDK package (in the tools directory)
+that can be used to identify which CPU cores correspond to which NUMA node.
+
+The QEMU IVSHMEM command line creation should be considered the last step before starting the virtual machine.
+Currently, there is no hot plug support for QEMU IVSHMEM devices,
+so one cannot add additional memory to an IVSHMEM device once it has been created.
+Therefore, the correct sequence to run an IVSHMEM application is to run host application first,
+obtain the command lines for each IVSHMEM device and then run all QEMU instances with guest applications afterwards.
+
+It is important to note that once QEMU is started, it holds on to the hugepages it uses for IVSHMEM devices.
+As a result, if the user wishes to shut down or restart the IVSHMEM host application,
+it is not enough to simply shut the application down.
+The virtual machine must also be shut down (if not, it will hold onto outdated host data).
Code Review / deb_dpdk.git / blobdiff