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 * Copyright © 2013-2014 University of Wisconsin-La Crosse.
 *                         All rights reserved.
 * Copyright © 2014 Cisco Systems, Inc.  All rights reserved.
 *
 * Copyright © 2014-2018 Inria.  All rights reserved.
 * See COPYING in top-level directory.
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 */

/*! \page netloc_intro Network Locality (netloc)

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Portable abstraction of network topologies for high-performance computing.

The netloc documentation spans of these sections:
<ul>
<li>
  \ref netloc_intro, this section below
</li>
<li>
  \ref netloc_scotch
</li>
</ul>



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\section netloc_summary Netloc Summary

The Portable Network Locality (netloc) software package provides network
topology discovery tools, and an abstract representation of those networks
topologies for a range of network types and configurations. It is provided as a
companion to the Portable Hardware Locality (hwloc) package. These two software
packages work together to provide a comprehensive view of the HPC system
topology, spanning from the processor cores in one server to the cores in
another - including the complex network(s) in between.

Towards this end, netloc is divided into two sets of components. The first
tools are for the admin to extract the information about the topology of the
machines with topology discovery tools for each network type and discovery
technique (called readers). The second set of tools is for the user to exploit
the collected information: to display the topology or create a
topology-aware mapping of the processes of an application.

\image html netloc_design.png
\image latex netloc_design.png "" width=9cm



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\subsection supportednetworks Supported Networks

For now, only InfiniBand (See \ref netloc_setup) is supported, but it is
planned to be extended it very soon.



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\section netloc_installation Netloc Installation

The generic installation procedure for both hwloc and netloc
is described in \ref common_installation.

Note that netloc is currently not supported on as many platforms as
the original hwloc project.
netloc is enabled by default when supported, or can be disabled
by passing <tt>\--disable-netloc</tt> to the configure command-line.



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\section netloc_setup Setup

To use Netloc tools, we need two steps. The first step consists in getting
information about network directly from tools distributed by manufacturers. For
Infiniband, for instance, this operation needs privileges to access to the
network device. For this step we have wrappers in Netloc that will call the
right tools with the right options.

The second step will transform the raw files generated by manufacturer tools,
into files in a format readable by Netloc tools, and that will not depend on
network technologies.

To be clear, let's take an example with Infiniband. This first step is handled by
\c netloc_ib_gather_raw that will call \c ibnetdiscover and \c ibroutes tools
to generate the necessary raw data files. The step has to be run by an
administrator, since the Infiniband tools need to access to the network device.

\verbatim
shell$ netloc_ib_gather_raw --help
Usage: netloc_ib_gather_raw [options] <outdir>
  Dumps topology information to <outdir>/ib-raw/
  Subnets are guessed from the <outdir>/hwloc/ directory where
  the hwloc XML exports of some nodes are stored.
Options:
 --sudo
    Pass sudo to internal ibnetdiscover and ibroute invocations.
    Useful when the entire script cannot run as root.
 --hwloc-dir <dir>
    Use <dir> instead of <outdir>/hwloc/ for hwloc XML exports.
 --force-subnet [<subnet>:]<board>:<port> to force the discovery
    Do not guess subnets from hwloc XML exports.
    Force discovery on local board <board> port <port>
    and optionally force the subnet id <subnet>
    instead of reading it from the first GID.
    Examples: --force-subnet mlx4_0:1
              --force-subnet fe80:0000:0000:0000:mlx4_0:1
 --ibnetdiscover /path/to/ibnetdiscover
 --ibroute /path/to/ibroute
    Specify exact location of programs. Default is /usr/bin/<program>
 --sleep <n>
    Sleep for <n> seconds between invocations of programs probing the network
 --ignore-errors
    Ignore errors from ibnetdiscover and ibroute, assume their outputs are ok
 --force -f
    Always rediscover to overwrite existing files without asking
 --verbose -v
    Add verbose messages
 --dry-run
    Do not actually run programs or modify anything
 --help -h
    Show this help

shell$ ./netloc_ib_gather_raw /home/netloc/data
WARNING: Not running as root.
Using /home/netloc/data/hwloc as hwloc lstopo XML directory.

Exporting local node hwloc XML...
  Running lstopo-no-graphics...

Found 1 subnets in hwloc directory:
 Subnet fe80:0000:0000:0000 is locally accessible from board qib0 port 1.

Looking at fe80:0000:0000:0000 (through local board qib0 port 1)...
 Running ibnetdiscover...
 Getting routes...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L112' LID 18...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L108' LID 20...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L102' LID 23...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L104' LID 25...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L106' LID 24...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L114' LID 22...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L116' LID 21...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L109' LID 12...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L111' LID 11...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L107' LID 13...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L103' LID 17...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L105' LID 16...
  Running ibroute for switch 'QLogic 12800-180 GUID=0x00066a00e8001310 L113' LID 15...
\endverbatim

The second step, that can be done by a regular user, is done by the tool \c
netloc_ib_extract_dats.

\verbatim
shell$ netloc_ib_extract_dats --help
Usage: netloc_ib_extract_dats <path to input raw data files> <output path> [--hwloc-dir
<hwloc xml path>]
        hwloc-dir can be an absolute path or a relative path from output path

shell$ netloc_ib_extract_dats /home/netloc/data/ib-raw /home/netloc/data/netloc \
  --hwloc-dir ../hwloc
Read subnet: fe80:0000:0000:0000
2 partitions found
        'node'
        'admin'
\endverbatim



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\section netloc_draw Topology display

Netloc provides a tool, \c netloc_draw.html, that displays a topology in a web
browser, by using a JSON file.

\subsection netloc_draw_setup Generate the JSON file

In order to display a topology, Netloc needs to generate a JSON file
corresponding to a topology. For this operation, the user must run \c
netloc_draw_to_json.

\verbatim
shell$ netloc_draw_to_json --help
Usage: netloc_draw_to_json <path to topology directory>

shell$ netloc_draw_to_json /home/netloc/data/netloc
\endverbatim

The \c netloc_draw_to_json command will write a JSON file for each topology
file found in the input directory. The output files, written also in the input
directory, can be open by \c netloc_draw.html in a web browser.

\subsection netloc_draw_tool Using netloc_draw

Once the JSON file is opened, the rendering is generated by the Javascript vis
library for computing the position of the nodes. From the interface, it is
possible to search for a specific node, to color the nodes, to expand merged
switches, to show statistics, to export as an image... The user can interact
with the nodes by moving them. For now, there are bugs and other nodes might
move too.

The placement of the nodes is done statically if the topology is detected as a
tree. If not, vis.js will use physics to find good positions, and it can be very
time consuming.

\image html netloc_draw.png
\image latex netloc_draw.png "" width=15cm

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\page netloc_scotch Netloc with Scotch

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Scotch is a toolbox for graph partitioning [XXX], that can do mapping between a
communication graph and an architecture. Netloc interfaces with Scotch, by
getting the topology of the machine and building the Scotch architecture. It is
also possible to directly build a mapping file that can be given to \c mpirun.

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\section scotch_intro Introduction

Scotch is able to deal architectures to represent the topology of a complete
machine. Scotch handles several types of topologies: complete graphs,
hypercubes, fat trees, meshes, torus, and random graphs.  Moreover, Scotch is
able to manage parts of architectures that are called sub-architectures. Thus,
from a complete architecture, we can create a sub-architecture that will
represent the available resources of the complete machine.

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\section scotch_setup Setup

The first step in order to use Netloc tools is to discover the network. For
this task, we provide tools called netloc_gather that are wrappers to the
dedicated tools provided by the manufacturer of the network, that generate the
raw data given by the devices. This task needs privileges to access to the
network devices. Once, this task is completed, the raw data is converted in a
generic format independent to the fabric by extract_dats. Figure 1 shows how
the different modules of Netloc are linked, and what are the tools provided by
Netloc.

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\section scotch_tools_api Tools and API

When the machine is discovered and all the needed files are generated as seen
previously, a user can call the netlocscotch functions from the API and
interact with Scotch.

\subsection netlocscotch_arch Build Scotch architectures

Netloc provides a function to export the built topology into the Scotch format.
That will give the possibility to the user to play with the topology in Scotch.
Since Netloc matches the discovered topology with known topologies, the Scotch
architecture won’t be random graphs but known topologies also in Scotch that
will lead to optimized graph algorithms. This function is called
netlocscotch_build_arch.

When the network topology is a tree, the topology converted by netlocscotch is
the complete topology of the machine containing intranode topologies from
hwloc. In this case, merging the two levels results in a bigger tree. For other
network topologies, the global graph created for Scotch is a generic graph
since it not not (at this moment) possible to create nested known
architectures.

\subsection netlocscotch_subarch Build Scotch sub-architectures

Most of the time, the user does not have access to the complete machine. He
uses a resource manager  to run his application and he will gain access only to
a set of nodes. In this case getting the Scotch architecture of the complete
machine is not relevant. Fortunately, Netloc is also able to build a Scotch
sub-architecture that will contain only the available nodes. For this operation
the user needs to run a specific program, netloc_get_resources, that will
record in a file, the lists of available nodes and available cores by using MPI
and hwloc. From this file, the function netlocscotch_build_subarch will build
the Scotch sub-architecture.

\subsection netlocscotch_mapping Mapping of processes

A main goal in having all these data about the network topology, especially in
Scotch structures, is to help the process placement. For that, we use the
mapping of a process graph to the architecture provided by Scotch. As we have
seen previously, Netloc is able to detect the structure of the topology and
will build the adapted Scotch architecture that will be more efficient than a
random structure.

In case, the network topology is not a tree, netlocscotch converts the complete
topology into a generic graph. The drawback in that is the Scotch graph
algorithms are less efficient. To overcome that, netlocscotch does two steps of
mapping: first it maps the processes to the nodes, and then for each node maps
the processes to the cores. We have to conduct tests to check if the method
gives better results than using a generic graph directly.

The other input needed in Scotch is the process graph. Since we want to
optimize the placement to decrease the communication time, a good metric for
building the application graph is the amount of communications between all
pairs of processes. Studies still have to be done to choose, in the most
efficient way, what we take into account to define the amount of communications
between the number of messages, the size of messages... This information will
be transformed into a process graph.

Once we have a good mapping computed by Scotch, we can give it to the user, or
Netloc can even generate the corresponding rank file useful to MPI.

*/
