19ffc1615d
Update the doc and release note. Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com> Acked-by: Helin Zhang <helin.zhang@intel.com> Acked-by: Vincent Jardin <vincent.jardin@6wind.com>
175 lines
8.0 KiB
ReStructuredText
175 lines
8.0 KiB
ReStructuredText
Design
|
|
======
|
|
|
|
Environment or Architecture-specific Sources
|
|
--------------------------------------------
|
|
|
|
In DPDK and DPDK applications, some code is specific to an architecture (i686, x86_64) or to an executive environment (bsdapp or linuxapp) and so on.
|
|
As far as is possible, all such instances of architecture or env-specific code should be provided via standard APIs in the EAL.
|
|
|
|
By convention, a file is common if it is not located in a directory indicating that it is specific.
|
|
For instance, a file located in a subdir of "x86_64" directory is specific to this architecture.
|
|
A file located in a subdir of "linuxapp" is specific to this execution environment.
|
|
|
|
.. note::
|
|
|
|
Code in DPDK libraries and applications should be generic.
|
|
The correct location for architecture or executive environment specific code is in the EAL.
|
|
|
|
When absolutely necessary, there are several ways to handle specific code:
|
|
|
|
* Use a ``#ifdef`` with the CONFIG option in the C code.
|
|
This can be done when the differences are small and they can be embedded in the same C file:
|
|
|
|
.. code-block:: c
|
|
|
|
#ifdef RTE_ARCH_I686
|
|
toto();
|
|
#else
|
|
titi();
|
|
#endif
|
|
|
|
* Use the CONFIG option in the Makefile. This is done when the differences are more significant.
|
|
In this case, the code is split into two separate files that are architecture or environment specific.
|
|
This should only apply inside the EAL library.
|
|
|
|
.. note::
|
|
|
|
As in the linux kernel, the ``CONFIG_`` prefix is not used in C code.
|
|
This is only needed in Makefiles or shell scripts.
|
|
|
|
Per Architecture Sources
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The following config options can be used:
|
|
|
|
* ``CONFIG_RTE_ARCH`` is a string that contains the name of the architecture.
|
|
* ``CONFIG_RTE_ARCH_I686``, ``CONFIG_RTE_ARCH_X86_64``, ``CONFIG_RTE_ARCH_X86_64_32`` or ``CONFIG_RTE_ARCH_PPC_64`` are defined only if we are building for those architectures.
|
|
|
|
Per Execution Environment Sources
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The following config options can be used:
|
|
|
|
* ``CONFIG_RTE_EXEC_ENV`` is a string that contains the name of the executive environment.
|
|
* ``CONFIG_RTE_EXEC_ENV_BSDAPP`` or ``CONFIG_RTE_EXEC_ENV_LINUXAPP`` are defined only if we are building for this execution environment.
|
|
|
|
Library Statistics
|
|
------------------
|
|
|
|
Description
|
|
~~~~~~~~~~~
|
|
|
|
This document describes the guidelines for DPDK library-level statistics counter
|
|
support. This includes guidelines for turning library statistics on and off and
|
|
requirements for preventing ABI changes when implementing statistics.
|
|
|
|
|
|
Mechanism to allow the application to turn library statistics on and off
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Each library that maintains statistics counters should provide a single build
|
|
time flag that decides whether the statistics counter collection is enabled or
|
|
not. This flag should be exposed as a variable within the DPDK configuration
|
|
file. When this flag is set, all the counters supported by current library are
|
|
collected for all the instances of every object type provided by the library.
|
|
When this flag is cleared, none of the counters supported by the current library
|
|
are collected for any instance of any object type provided by the library:
|
|
|
|
.. code-block:: console
|
|
|
|
# DPDK file config/common_linuxapp, config/common_bsdapp, etc.
|
|
CONFIG_RTE_<LIBRARY_NAME>_STATS_COLLECT=y/n
|
|
|
|
The default value for this DPDK configuration file variable (either "yes" or
|
|
"no") is decided by each library.
|
|
|
|
|
|
Prevention of ABI changes due to library statistics support
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The layout of data structures and prototype of functions that are part of the
|
|
library API should not be affected by whether the collection of statistics
|
|
counters is turned on or off for the current library. In practical terms, this
|
|
means that space should always be allocated in the API data structures for
|
|
statistics counters and the statistics related API functions are always built
|
|
into the code, regardless of whether the statistics counter collection is turned
|
|
on or off for the current library.
|
|
|
|
When the collection of statistics counters for the current library is turned
|
|
off, the counters retrieved through the statistics related API functions should
|
|
have a default value of zero.
|
|
|
|
|
|
Motivation to allow the application to turn library statistics on and off
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
It is highly recommended that each library provides statistics counters to allow
|
|
an application to monitor the library-level run-time events. Typical counters
|
|
are: number of packets received/dropped/transmitted, number of buffers
|
|
allocated/freed, number of occurrences for specific events, etc.
|
|
|
|
However, the resources consumed for library-level statistics counter collection
|
|
have to be spent out of the application budget and the counters collected by
|
|
some libraries might not be relevant to the current application. In order to
|
|
avoid any unwanted waste of resources and/or performance impacts, the
|
|
application should decide at build time whether the collection of library-level
|
|
statistics counters should be turned on or off for each library individually.
|
|
|
|
Library-level statistics counters can be relevant or not for specific
|
|
applications:
|
|
|
|
* For Application A, counters maintained by Library X are always relevant and
|
|
the application needs to use them to implement certain features, such as traffic
|
|
accounting, logging, application-level statistics, etc. In this case,
|
|
the application requires that collection of statistics counters for Library X is
|
|
always turned on.
|
|
|
|
* For Application B, counters maintained by Library X are only useful during the
|
|
application debug stage and are not relevant once debug phase is over. In this
|
|
case, the application may decide to turn on the collection of Library X
|
|
statistics counters during the debug phase and at a later stage turn them off.
|
|
|
|
* For Application C, counters maintained by Library X are not relevant at all.
|
|
It might be that the application maintains its own set of statistics counters
|
|
that monitor a different set of run-time events (e.g. number of connection
|
|
requests, number of active users, etc). It might also be that the application
|
|
uses multiple libraries (Library X, Library Y, etc) and it is interested in the
|
|
statistics counters of Library Y, but not in those of Library X. In this case,
|
|
the application may decide to turn the collection of statistics counters off for
|
|
Library X and on for Library Y.
|
|
|
|
The statistics collection consumes a certain amount of CPU resources (cycles,
|
|
cache bandwidth, memory bandwidth, etc) that depends on:
|
|
|
|
* Number of libraries used by the current application that have statistics
|
|
counters collection turned on.
|
|
|
|
* Number of statistics counters maintained by each library per object type
|
|
instance (e.g. per port, table, pipeline, thread, etc).
|
|
|
|
* Number of instances created for each object type supported by each library.
|
|
|
|
* Complexity of the statistics logic collection for each counter: when only
|
|
some occurrences of a specific event are valid, additional logic is typically
|
|
needed to decide whether the current occurrence of the event should be counted
|
|
or not. For example, in the event of packet reception, when only TCP packets
|
|
with destination port within a certain range should be recorded, conditional
|
|
branches are usually required. When processing a burst of packets that have been
|
|
validated for header integrity, counting the number of bits set in a bitmask
|
|
might be needed.
|
|
|
|
PF and VF Considerations
|
|
------------------------
|
|
|
|
The primary goal of DPDK is to provide a userspace dataplane. Managing VFs from
|
|
a PF driver is a control plane feature and developers should generally rely on
|
|
the Linux Kernel for that.
|
|
|
|
Developers should work with the Linux Kernel community to get the required
|
|
functionality upstream. PF functionality should only be added to DPDK for
|
|
testing and prototyping purposes while the kernel work is ongoing. It should
|
|
also be marked with an "EXPERIMENTAL" tag. If the functionality isn't
|
|
upstreamable then a case can be made to maintain the PF functionality in DPDK
|
|
without the EXPERIMENTAL tag.
|