Ubuntu Manpage: ibacm - address and route resolution services for InfiniBand.

NAME

       ibacm - address and route resolution services for InfiniBand.

SYNOPSIS

       ibacm [-D] [-P] [-A addr_file] [-O option_file]

DESCRIPTION

The IB ACM implements and provides a framework for name, address, and route (path) resolution services
over InfiniBand. It is intended to address connection setup scalability issues running MPI applications
on large clusters. The IB ACM provides information needed to establish a connection, but does not
implement the CM protocol.

A primary user of the ibacm service is the librdmacm library. This enables applications to make use of
the ibacm service without code changes or needing to be aware that the service is in use. librdmacm
versions 1.0.12 - 1.0.15 can invoke IB ACM services when built using the --with-ib_acm option. Version
1.0.16 and newer of librdmacm will automatically use the IB ACM if it is installed. The IB ACM services
tie in under the rdma_resolve_addr, rdma_resolve_route, and rdma_getaddrinfo routines. For maximum
benefit, the rdma_getaddrinfo routine should be used, however existing applications should still see
significant connection scaling benefits using the calls available in librdmacm 1.0.11 and previous
releases.

The IB ACM is focused on being scalable, efficient, and extensible. It implements a plugin architecture
that allows a vendor to supply its proprietary provider in addition to the default provider. The current
default provider implementation ibacmp limits network traffic, SA interactions, and centralized services.
Ibacmp supports multiple resolution protocols in order to handle different fabric topologies.

The IB ACM package is comprised of three components: the ibacm core service, the default provider ibacmp
shared library, and a test/configuration utility - ib_acme. All three are userspace components and are
available for Linux. Additional details are given below.

OPTIONS

       -D     run in daemon mode (default)

       -P     run as standard process

       -A addr_file
              address configuration file

       -O option_file
              option configuration file

       --systemd
              Enable systemd integration. This includes optional socket activation  of  the  daemon's  listening
              socket.

QUICK START GUIDE

       1.  Prerequisites: libibverbs and libibumad must be installed.  The IB stack should be running with IPoIB
       configured.  These steps assume that the user has administrative privileges.

       2. Install the IB ACM package.  This installs ibacm, ibacmp, ib_acme, and init.d scripts.

       3. Run 'ibacm' as administrator to start the ibacm daemon.

       4. Optionally, run 'ib_acme -d <dest_ip> -v' to verify that the ibacm service is running.

       5. Install librdmacm, using the build option --with-ib_acm if needed.  This build option  is  not  needed
       with  librdmacm  1.0.17  or newer.  The librdmacm will automatically use the ibacm service.  On failures,
       the librdmacm will fall back to normal resolution.

       6. You can use ib_acme -P to gather performance statistics from the local ibacm  daemon  to  see  if  the
       service is working correctly.  Similarly, the command ib_acme -e could be used to enumerate all endpoints
       created by the local ibacm service.

NOTES

ib_acme:

The ib_acme program serves a dual role. It acts as a utility to test ibacm operation and help verify if
the ibacm service and selected protocol is usable for a given cluster configuration. Additionally, it
automatically generates ibacm configuration files to assist with or eliminate manual setup.

ibacm configuration files:

The ibacm service relies on two configuration files.

The ibacm_addr.cfg file contains name and address mappings for each IB <device, port, pkey> endpoint.
Although the names in the ibacm_addr.cfg file can be anything, ib_acme maps the host name to the IB
endpoints. IP addresses, on the other hand, are assigned dynamically. If the address file cannot be
found, the ibacm service will attempt to create one using default values.

The ibacm_opts.cfg file provides a set of configurable options for the ibacm core service and default
provider, such as timeout, number of retries, logging level, etc. ib_acme generates the ibacm_opts.cfg
file using static information. If an option file cannot be found, ibacm will use default values.

ibacm:

The ibacm service is responsible for resolving names and addresses to InfiniBand path information and
caching such data. It should execute with administrative privileges.

The ibacm implements a client interface over TCP sockets, which is abstracted by the librdmacm library.
One or more providers can be loaded by the core service, depending on the configuration. In the default
provider ibacmp, one or more back-end protocols are used to satisfy user requests. Although ibacmp
supports standard SA path record queries on the back-end, it also supports a resolution protocol based on
multicast traffic. The latter is not usable on all fabric topologies, specifically ones that may not
have reversible paths or fabrics using torus routing. Users should use the ib_acme utility to verify
that multicast protocol is usable before running other applications.

Conceptually, the default provider ibacmp implements an ARP like protocol and either uses IB multicast
records to construct path record data or queries the SA directly, depending on the selected route
protocol. By default, the ibacmp provider uses and caches SA path record queries.

Specifically, all IB endpoints join a number of multicast groups. Multicast groups differ based on
rates, mtu, sl, etc., and are prioritized. All participating endpoints must be able to communicate on
the lowest priority multicast group. The ibacmp assigns one or more names/addresses to each IB endpoint
using the ibacm_addr.cfg file. Clients provide source and destination names or addresses as input to the
service, and receive as output path record data.

The service maps a client's source name/address to a local IB endpoint. If the destination name/address
is not cached locally in the default provider, it sends a multicast request out on the lowest priority
multicast group on the local endpoint. The request carries a list of multicast groups that the sender
can use. The recipient of the request selects the highest priority multicast group that it can use as
well and returns that information directly to the sender. The request data is cached by all endpoints
that receive the multicast request message. The source endpoint also caches the response and uses the
multicast group that was selected to construct or obtain path record data, which is returned to the
client.

The current implementation of the provider ibacmp has several additional restrictions:

- The ibacmp is limited in its handling of dynamic changes. ibacm must be stopped and restarted if a
cluster is reconfigured.

- Support for IPv6 has not been verified.

- The number of multicast groups that an endpoint can support is limited to 2.

The ibacmp contains several internal caches. These include caches for GID and LID destination addresses.
These caches can be optionally preloaded. ibacm supports the OpenSM dump_pr plugin "full" PathRecord
format which is used to preload these caches. The file format is specified in the ibacm_opts.cfg file
via the route_preload setting which should be set to full_opensm_v1 for this file format. Default format
is none which does not preload these caches. See dump_pr.notes.txt in dump_pr for more information on
the full_opensm_v1 file format and how to configure OpenSM to generate this file.