opensm - InfiniBand subnet manager and administration (SM/SA)
opensm [--version]] [-F | --config <file_name>] [-c(reate-config)
<file_name>] [-g(uid) <GUID in hex>] [-l(mc) <LMC>] [-p(riority)
<PRIORITY>] [-smkey <SM_Key>] [-r(eassign_lids)] [-R <engine name(s)> |
--routing_engine <engine name(s)>] [-A | --ucast_cache] [-z |
--connect_roots] [-M <file name> | --lid_matrix_file <file name>] [-U
<file name> | --lfts_file <file name>] [-S | --sadb_file <file name>]
[-a | --root_guid_file <path to file>] [-u | --cn_guid_file <path to
file>] [-X | --guid_routing_order_file <path to file>] [-m |
--ids_guid_file <path to file>] [-o(nce)] [-s(weep) <interval>]
[-t(imeout) <milliseconds>] [-maxsmps <number>] [-console [off | local
| socket | loopback]] [-console-port <port>] [-i(gnore-guids)
<equalize-ignore-guids-file>] [-f <log file path> | --log_file <log
file path> ] [-L | --log_limit <size in MB>] [-e(rase_log_file)]
[-P(config) <partition config file> ] [-N | --no_part_enforce] [-Q |
--qos [-Y | --qos_policy_file <file name>]] [-y | --stay_on_fatal] [-B
| --daemon] [-I | --inactive] [--perfmgr] [--perfmgr_sweep_time_s
<seconds>] [--prefix_routes_file <path>] [--consolidate_ipv6_snm_req]
[-v(erbose)] [-V] [-D <flags>] [-d(ebug) <number>] [-h(elp)] [-?]
opensm is an InfiniBand compliant Subnet Manager and Administration,
and runs on top of OpenIB.
opensm provides an implementation of an InfiniBand Subnet Manager and
Administration. Such a software entity is required to run for in order
to initialize the InfiniBand hardware (at least one per each InfiniBand
opensm also now contains an experimental version of a performance
manager as well.
opensm defaults were designed to meet the common case usage on clusters
with up to a few hundred nodes. Thus, in this default mode, opensm will
scan the IB fabric, initialize it, and sweep occasionally for changes.
opensm attaches to a specific IB port on the local machine and
configures only the fabric connected to it. (If the local machine has
other IB ports, opensm will ignore the fabrics connected to those other
ports). If no port is specified, it will select the first "best"
opensm can present the available ports and prompt for a port number to
By default, the run is logged to two files: /var/log/messages and
/var/log/opensm.log. The first file will register only general major
events, whereas the second will include details of reported errors. All
errors reported in this second file should be treated as indicators of
IB fabric health issues. (Note that when a fatal and non-recoverable
error occurs, opensm will exit.) Both log files should include the
message "SUBNET UP" if opensm was able to setup the subnet correctly.
Prints OpenSM version and exits.
-F, --config <config file>
The name of the OpenSM config file. When not specified
/etc/opensm/opensm.conf will be used (if exists).
-c, --create-config <file name>
OpenSM will dump its configuration to the specified file and
exit. This is a way to generate OpenSM configuration file
-g, --guid <GUID in hex>
This option specifies the local port GUID value with which
OpenSM should bind. OpenSM may be bound to 1 port at a time.
If GUID given is 0, OpenSM displays a list of possible port
GUIDs and waits for user input. Without -g, OpenSM tries to use
the default port.
-l, --lmc <LMC value>
This option specifies the subnet’s LMC value. The number of
LIDs assigned to each port is 2^LMC. The LMC value must be in
the range 0-7. LMC values > 0 allow multiple paths between
ports. LMC values > 0 should only be used if the subnet
topology actually provides multiple paths between ports, i.e.
multiple interconnects between switches. Without -l, OpenSM
defaults to LMC = 0, which allows one path between any two
-p, --priority <Priority value>
This option specifies the SM´s PRIORITY. This will effect the
handover cases, where master is chosen by priority and GUID.
Range goes from 0 (default and lowest priority) to 15 (highest).
-smkey <SM_Key value>
This option specifies the SM´s SM_Key (64 bits). This will
effect SM authentication. Note that OpenSM version 3.2.1 and
below used the default value ’1’ in a host byte order, it is
fixed now but you may need this option to interoperate with old
OpenSM running on a little endian machine.
This option causes OpenSM to reassign LIDs to all end nodes.
Specifying -r on a running subnet may disrupt subnet traffic.
Without -r, OpenSM attempts to preserve existing LID assignments
resolving multiple use of same LID.
-R, --routing_engine <Routing engine names>
This option chooses routing engine(s) to use instead of Min Hop
algorithm (default). Multiple routing engines can be specified
separated by commas so that specific ordering of routing
algorithms will be tried if earlier routing engines fail.
Supported engines: minhop, updn, file, ftree, lash, dor
This option enables unicast routing cache and prevents routing
recalculation (which is a heavy task in a large cluster) when
there was no topology change detected during the heavy sweep, or
when the topology change does not require new routing
calculation, e.g. when one or more CAs/RTRs/leaf switches going
down, or one or more of these nodes coming back after being
down. A very common case that is handled by the unicast routing
cache is host reboot, which otherwise would cause two full
routing recalculations: one when the host goes down, and the
other when the host comes back online.
This option enforces a routing engine (currently up/down only)
to make connectivity between root switches and in this way to be
fully IBA complaint. In many cases this can violate "pure"
deadlock free algorithm, so use it carefully.
-M, --lid_matrix_file <file name>
This option specifies the name of the lid matrix dump file from
where switch lid matrices (min hops tables will be loaded.
-U, --lfts_file <file name>
This option specifies the name of the LFTs file from where
switch forwarding tables will be loaded.
-S, --sadb_file <file name>
This option specifies the name of the SA DB dump file from where
SA database will be loaded.
-a, --root_guid_file <file name>
Set the root nodes for the Up/Down or Fat-Tree routing algorithm
to the guids provided in the given file (one to a line).
-u, --cn_guid_file <file name>
Set the compute nodes for the Fat-Tree routing algorithm to the
guids provided in the given file (one to a line).
-m, --ids_guid_file <file name>
Name of the map file with set of the IDs which will be used by
Up/Down routing algorithm instead of node GUIDs (format: <guid>
<id> per line).
-X, --guid_routing_order_file <file name>
Set the order port guids will be routed for the MinHop and
Up/Down routing algorithms to the guids provided in the given
file (one to a line).
This option causes OpenSM to configure the subnet once, then
exit. Ports remain in the ACTIVE state.
-s, --sweep <interval value>
This option specifies the number of seconds between subnet
sweeps. Specifying -s 0 disables sweeping. Without -s, OpenSM
defaults to a sweep interval of 10 seconds.
-t, --timeout <value>
This option specifies the time in milliseconds used for
transaction timeouts. Specifying -t 0 disables timeouts.
Without -t, OpenSM defaults to a timeout value of 200
This option specifies the number of VL15 SMP MADs allowed on the
wire at any one time. Specifying -maxsmps 0 allows unlimited
outstanding SMPs. Without -maxsmps, OpenSM defaults to a
maximum of 4 outstanding SMPs.
-console [off | local | socket | loopback]
This option brings up the OpenSM console (default off). Note
that the socket and loopback options will only be available if
OpenSM was built with --enable-console-socket.
Specify an alternate telnet port for the socket console (default
10000). Note that this option only appears if OpenSM was built
-i, -ignore-guids <equalize-ignore-guids-file>
This option provides the means to define a set of ports (by node
guid and port number) that will be ignored by the link load
This option forces OpenSM to honor the guid2lid file, when it
comes out of Standby state, if such file exists under
OSM_CACHE_DIR, and is valid. By default, this is FALSE.
-f, --log_file <file name>
This option defines the log to be the given file. By default,
the log goes to /var/log/opensm.log. For the log to go to
standard output use -f stdout.
-L, --log_limit <size in MB>
This option defines maximal log file size in MB. When specified
the log file will be truncated upon reaching this limit.
This option will cause deletion of the log file (if it
previously exists). By default, the log file is accumulative.
-P, --Pconfig <partition config file>
This option defines the optional partition configuration file.
The default name is /etc/opensm/partitions.conf.
--prefix_routes_file <file name>
Prefix routes control how the SA responds to path record queries
for off-subnet DGIDs. By default, the SA fails such queries.
The PREFIX ROUTES section below describes the format of the
configuration file. The default path is
This option enables QoS setup. It is disabled by default.
-Y, --qos_policy_file <file name>
This option defines the optional QoS policy file. The default
name is /etc/opensm/qos-policy.conf.
This option disables partition enforcement on switch external
This option will cause SM not to exit on fatal initialization
issues: if SM discovers duplicated guids or a 12x link with lane
reversal badly configured. By default, the SM will exit on
Run in daemon mode - OpenSM will run in the background.
Start SM in inactive rather than init SM state. This option can
be used in conjunction with the perfmgr so as to run a
standalone performance manager without SM/SA. However, this is
NOT currently implemented in the performance manager.
Enable the perfmgr. Only takes effect if --enable-perfmgr was
specified at configure time.
Specify the sweep time for the performance manager in seconds
(default is 180 seconds). Only takes effect if --enable-perfmgr
was specified at configure time.
Consolidate IPv6 Solicited Node Multicast group join requests
into one multicast group per MGID PKey.
This option increases the log verbosity level. The -v option
may be specified multiple times to further increase the
verbosity level. See the -D option for more information about
-V This option sets the maximum verbosity level and forces log
flushing. The -V option is equivalent to ´-D 0xFF -d 2´. See
the -D option for more information about log verbosity.
This option sets the log verbosity level. A flags field must
follow the -D option. A bit set/clear in the flags
enables/disables a specific log level as follows:
BIT LOG LEVEL ENABLED
0x01 - ERROR (error messages)
0x02 - INFO (basic messages, low volume)
0x04 - VERBOSE (interesting stuff, moderate volume)
0x08 - DEBUG (diagnostic, high volume)
0x10 - FUNCS (function entry/exit, very high volume)
0x20 - FRAMES (dumps all SMP and GMP frames)
0x40 - ROUTING (dump FDB routing information)
0x80 - currently unused.
Without -D, OpenSM defaults to ERROR + INFO (0x3). Specifying
-D 0 disables all messages. Specifying -D 0xFF enables all
messages (see -V). High verbosity levels may require increasing
the transaction timeout with the -t option.
-d, --debug <value>
This option specifies a debug option. These options are not
normally needed. The number following -d selects the debug
option to enable as follows:
-d0 - Ignore other SM nodes
-d1 - Force single threaded dispatching
-d2 - Force log flushing after each log message
-d3 - Disable multicast support
Display this usage info then exit.
-? Display this usage info then exit.
The following environment variables control opensm behavior:
OSM_TMP_DIR - controls the directory in which the temporary files
generated by opensm are created. These files are: opensm-subnet.lst,
opensm.fdbs, and opensm.mcfdbs. By default, this directory is /var/log.
OSM_CACHE_DIR - opensm stores certain data to the disk such that
subsequent runs are consistent. The default directory used is
/var/cache/opensm. The following file is included in it:
guid2lid - stores the LID range assigned to each GUID
When opensm receives a HUP signal, it starts a new heavy sweep as if a
trap was received or a topology change was found.
Also, SIGUSR1 can be used to trigger a reopen of /var/log/opensm.log
for logrotate purposes.
The default name of OpenSM partitions configuration file is
/etc/opensm/partitions.conf. The default may be changed by using
--Pconfig (-P) option with OpenSM.
The default partition will be created by OpenSM unconditionally even
when partition configuration file does not exist or cannot be accessed.
The default partition has P_Key value 0x7fff. OpenSM´s port will have
full membership in default partition. All other end ports will have
Line content followed after ´#´ character is comment and ignored by
General file format:
<Partition Definition>:<PortGUIDs list> ;
PartitionName - string, will be used with logging. When omitted
empty string will be used.
PKey - P_Key value for this partition. Only low 15 bits will
be used. When omitted will be autogenerated.
flag - used to indicate IPoIB capability of this partition.
defmember=full|limited - specifies default membership for port guid
list. Default is limited.
Currently recognized flags are:
ipoib - indicates that this partition may be used for IPoIB, as
result IPoIB capable MC group will be created.
rate=<val> - specifies rate for this IPoIB MC group
(default is 3 (10GBps))
mtu=<val> - specifies MTU for this IPoIB MC group
(default is 4 (2048))
sl=<val> - specifies SL for this IPoIB MC group
(default is 0)
scope=<val> - specifies scope for this IPoIB MC group
(default is 2 (link local)). Multiple scope settings
are permitted for a partition.
Note that values for rate, mtu, and scope should be specified as
defined in the IBTA specification (for example, mtu=4 for 2048).
PortGUID - GUID of partition member EndPort. Hexadecimal
numbers should start from 0x, decimal numbers
are accepted too.
full or limited - indicates full or limited membership for this
port. When omitted (or unrecognized) limited
membership is assumed.
There are two useful keywords for PortGUID definition:
- ’ALL’ means all end ports in this subnet.
- ’SELF’ means subnet manager’s port.
Empty list means no ports in this partition.
White space is permitted between delimiters (’=’, ’,’,’:’,’;’).
The line can be wrapped after ’:’ followed after Partition Definition
PartitionName does not need to be unique, PKey does need to be unique.
If PKey is repeated then those partition configurations will be merged
and first PartitionName will be used (see also next note).
It is possible to split partition configuration in more than one
definition, but then PKey should be explicitly specified (otherwise
different PKey values will be generated for those definitions).
Default=0x7fff : ALL, SELF=full ;
NewPartition , ipoib : 0x123456=full, 0x3456789034=limi, 0x2134af2306
YetAnotherOne = 0x300 : SELF=full ;
YetAnotherOne = 0x300 : ALL=limited ;
ShareIO = 0x80 , defmember=full : 0x123451, 0x123452;
# 0x123453, 0x123454 will be limited
ShareIO = 0x80 : 0x123453, 0x123454, 0x123455=full;
# 0x123456, 0x123457 will be limited
ShareIO = 0x80 : defmember=limited : 0x123456, 0x123457,
ShareIO = 0x80 , defmember=full : 0x123459, 0x12345a;
ShareIO = 0x80 , defmember=full : 0x12345b, 0x12345c=limited,
The following rule is equivalent to how OpenSM used to run prior to the
There are a set of QoS related low-level configuration parameters. All
these parameter names are prefixed by "qos_" string. Here is a full
list of these parameters:
qos_max_vls - The maximum number of VLs that will be on the subnet
qos_high_limit - The limit of High Priority component of VL
Arbitration table (IBA 7.6.9)
qos_vlarb_low - Low priority VL Arbitration table (IBA 7.6.9)
qos_vlarb_high - High priority VL Arbitration table (IBA 7.6.9)
Both VL arbitration templates are pairs of
VL and weight
qos_sl2vl - SL2VL Mapping table (IBA 7.6.6) template. It is
a list of VLs corresponding to SLs 0-15 (Note
that VL15 used here means drop this SL)
Typical default values (hard-coded in OpenSM initialization) are:
The syntax is compatible with rest of OpenSM configuration options and
values may be stored in OpenSM config file (cached options file).
In addition to the above, we may define separate QoS configuration
parameters sets for various target types. As targets, we currently
support CAs, routers, switch external ports, and switch’s enhanced port
0. The names of such specialized parameters are prefixed by
"qos_<type>_" string. Here is a full list of the currently supported
qos_ca_ - QoS configuration parameters set for CAs.
qos_rtr_ - parameters set for routers.
qos_sw0_ - parameters set for switches’ port 0.
qos_swe_ - parameters set for switches’ external ports.
Prefix routes control how the SA responds to path record queries for
off-subnet DGIDs. By default, the SA fails such queries. Note that
IBA does not specify how the SA should obtain off-subnet path record
information. The prefix routes configuration is meant as a stop-gap
until the specification is completed.
Each line in the configuration file is a 64-bit prefix followed by a
64-bit GUID, separated by white space. The GUID specifies the router
port on the local subnet that will handle the prefix. Blank lines are
ignored, as is anything between a # character and the end of the line.
The prefix and GUID are both in hex, the leading 0x is optional.
Either, or both, can be wild-carded by specifying an asterisk instead
of an explicit prefix or GUID.
When responding to a path record query for an off-subnet DGID, opensm
searches for the first prefix match in the configuration file.
Therefore, the order of the lines in the configuration file is
important: a wild-carded prefix at the beginning of the configuration
file renders all subsequent lines useless. If there is no match, then
opensm fails the query. It is legal to repeat prefixes in the
configuration file, opensm will return the path to the first available
matching router. A configuration file with a single line where both
prefix and GUID are wild-carded means that a path record query
specifying any off-subnet DGID should return a path to the first
available router. This configuration yields the same behaviour
formerly achieved by compiling opensm with -DROUTER_EXP.
OpenSM now offers five routing engines:
1. Min Hop Algorithm - based on the minimum hops to each node where
the path length is optimized.
2. UPDN Unicast routing algorithm - also based on the minimum hops to
each node, but it is constrained to ranking rules. This algorithm
should be chosen if the subnet is not a pure Fat Tree, and deadlock may
occur due to a loop in the subnet.
3. Fat Tree Unicast routing algorithm - this algorithm optimizes
routing for congestion-free "shift" communication pattern. It should
be chosen if a subnet is a symmetrical or almost symmetrical fat-tree
of various types, not just K-ary-N-Trees: non-constant K, not fully
staffed, any Constant Bisectional Bandwidth (CBB) ratio. Similar to
UPDN, Fat Tree routing is constrained to ranking rules.
4. LASH unicast routing algorithm - uses Infiniband virtual layers (SL)
to provide deadlock-free shortest-path routing while also distributing
the paths between layers. LASH is an alternative deadlock-free
topology-agnostic routing algorithm to the non-minimal UPDN algorithm
avoiding the use of a potentially congested root node.
5. DOR Unicast routing algorithm - based on the Min Hop algorithm, but
avoids port equalization except for redundant links between the same
two switches. This provides deadlock free routes for hypercubes when
the fabric is cabled as a hypercube and for meshes when cabled as a
mesh (see details below).
OpenSM also supports a file method which can load routes from a table.
See ´Modular Routing Engine´ for more information on this.
The basic routing algorithm is comprised of two stages:
1. MinHop matrix calculation
How many hops are required to get from each port to each LID ?
The algorithm to fill these tables is different if you run standard
(min hop) or Up/Down.
For standard routing, a "relaxation" algorithm is used to propagate
min hop from every destination LID through neighbor switches
For Up/Down routing, a BFS from every target is used. The BFS tracks
link direction (up or down) and avoid steps that will perform up after
a down step was used.
2. Once MinHop matrices exist, each switch is visited and for each
target LID a decision is made as to what port should be used to get to
This step is common to standard and Up/Down routing. Each port has a
counter counting the number of target LIDs going through it.
When there are multiple alternative ports with same MinHop to a LID,
the one with less previously assigned ports is selected.
If LMC > 0, more checks are added: Within each group of LIDs
assigned to same target port,
a. use only ports which have same MinHop
b. first prefer the ones that go to different systemImageGuid (then
the previous LID of the same LMC group)
c. if none - prefer those which go through another NodeGuid
d. fall back to the number of paths method (if all go to same node).
Effect of Topology Changes
OpenSM will preserve existing routing in any case where there is no
change in the fabric switches unless the -r (--reassign_lids) option is
This option causes OpenSM to reassign LIDs to all
end nodes. Specifying -r on a running subnet
may disrupt subnet traffic.
Without -r, OpenSM attempts to preserve existing
LID assignments resolving multiple use of same LID.
If a link is added or removed, OpenSM does not recalculate the routes
that do not have to change. A route has to change if the port is no
longer UP or no longer the MinHop. When routing changes are performed,
the same algorithm for balancing the routes is invoked.
In the case of using the file based routing, any topology changes are
currently ignored The ’file’ routing engine just loads the LFTs from
the file specified, with no reaction to real topology. Obviously, this
will not be able to recheck LIDs (by GUID) for disconnected nodes, and
LFTs for non-existent switches will be skipped. Multicast is not
affected by ’file’ routing engine (this uses min hop tables).
Min Hop Algorithm
The Min Hop algorithm is invoked by default if no routing algorithm is
specified. It can also be invoked by specifying ’-R minhop’.
The Min Hop algorithm is divided into two stages: computation of min-
hop tables on every switch and LFT output port assignment. Link
subscription is also equalized with the ability to override based on
port GUID. The latter is supplied by:
This option provides the means to define a set of ports
(by guid) that will be ignored by the link load
equalization algorithm. Note that only endports (CA,
switch port 0, and router ports) and not switch external
ports are supported.
LMC awareness routes based on (remote) system or switch basis.
Purpose of UPDN Algorithm
The UPDN algorithm is designed to prevent deadlocks from occurring in
loops of the subnet. A loop-deadlock is a situation in which it is no
longer possible to send data between any two hosts connected through
the loop. As such, the UPDN routing algorithm should be used if the
subnet is not a pure Fat Tree, and one of its loops may experience a
deadlock (due, for example, to high pressure).
The UPDN algorithm is based on the following main stages:
1. Auto-detect root nodes - based on the CA hop length from any switch
in the subnet, a statistical histogram is built for each switch (hop
num vs number of occurrences). If the histogram reflects a specific
column (higher than others) for a certain node, then it is marked as a
root node. Since the algorithm is statistical, it may not find any root
nodes. The list of the root nodes found by this auto-detect stage is
used by the ranking process stage.
Note 1: The user can override the node list manually.
Note 2: If this stage cannot find any root nodes, and the user did
not specify a guid list file, OpenSM defaults back to the
Min Hop routing algorithm.
2. Ranking process - All root switch nodes (found in stage 1) are
assigned a rank of 0. Using the BFS algorithm, the rest of the switch
nodes in the subnet are ranked incrementally. This ranking aids in the
process of enforcing rules that ensure loop-free paths.
3. Min Hop Table setting - after ranking is done, a BFS algorithm is
run from each (CA or switch) node in the subnet. During the BFS
process, the FDB table of each switch node traversed by BFS is updated,
in reference to the starting node, based on the ranking rules and guid
At the end of the process, the updated FDB tables ensure loop-free
paths through the subnet.
Note: Up/Down routing does not allow LID routing communication between
switches that are located inside spine "switch systems". The reason is
that there is no way to allow a LID route between them that does not
break the Up/Down rule. One ramification of this is that you cannot
run SM on switches other than the leaf switches of the fabric.
UPDN Algorithm Usage
Activation through OpenSM
Use ’-R updn’ option (instead of old ’-u’) to activate the UPDN
algorithm. Use ’-a <root_guid_file>’ for adding an UPDN guid file that
contains the root nodes for ranking. If the ‘-a’ option is not used,
OpenSM uses its auto-detect root nodes algorithm.
Notes on the guid list file:
1. A valid guid file specifies one guid in each line. Lines with an
invalid format will be discarded.
2. The user should specify the root switch guids. However, it is also
possible to specify CA guids; OpenSM will use the guid of the switch
(if it exists) that connects the CA to the subnet as a root node.
Fat-tree Routing Algorithm
The fat-tree algorithm optimizes routing for "shift" communication
pattern. It should be chosen if a subnet is a symmetrical or almost
symmetrical fat-tree of various types. It supports not just K-ary-N-
Trees, by handling for non-constant K, cases where not all leafs (CAs)
are present, any CBB ratio. As in UPDN, fat-tree also prevents credit-
If the root guid file is not provided (’-a’ or ’--root_guid_file’
options), the topology has to be pure fat-tree that complies with the
- Tree rank should be between two and eight (inclusively)
- Switches of the same rank should have the same number
of UP-going port groups*, unless they are root switches,
in which case the shouldn’t have UP-going ports at all.
- Switches of the same rank should have the same number
of DOWN-going port groups, unless they are leaf switches.
- Switches of the same rank should have the same number
of ports in each UP-going port group.
- Switches of the same rank should have the same number
of ports in each DOWN-going port group.
- All the CAs have to be at the same tree level (rank).
If the root guid file is provided, the topology doesn’t have to be pure
fat-tree, and it should only comply with the following rules:
- Tree rank should be between two and eight (inclusively)
- All the Compute Nodes** have to be at the same tree level (rank).
Note that non-compute node CAs are allowed here to be at different
* ports that are connected to the same remote switch are referenced as
** list of compute nodes (CNs) can be specified by ´-u´ or
´--cn_guid_file´ OpenSM options.
Topologies that do not comply cause a fallback to min hop routing.
Note that this can also occur on link failures which cause the topology
to no longer be "pure" fat-tree.
Note that although fat-tree algorithm supports trees with non-integer
CBB ratio, the routing will not be as balanced as in case of integer
CBB ratio. In addition to this, although the algorithm allows leaf
switches to have any number of CAs, the closer the tree is to be fully
populated, the more effective the "shift" communication pattern will
be. In general, even if the root list is provided, the closer the
topology to a pure and symmetrical fat-tree, the more optimal the
routing will be.
The algorithm also dumps compute node ordering file (opensm-ftree-ca-
order.dump) in the same directory where the OpenSM log resides. This
ordering file provides the CN order that may be used to create
efficient communication pattern, that will match the routing tables.
Activation through OpenSM
Use ’-R ftree’ option to activate the fat-tree algorithm. Use ’-a
<root_guid_file>’ to provide root nodes for ranking. If the ‘-a’ option
is not used, routing algorithm will detect roots automatically. Use
’-u <root_cn_file>’ to provide the list of compute nodes. If the ‘-u’
option is not used, all the CAs are considered as compute nodes.
Note: LMC > 0 is not supported by fat-tree routing. If this is
specified, the default routing algorithm is invoked instead.
LASH Routing Algorithm
LASH is an acronym for LAyered SHortest Path Routing. It is a
deterministic shortest path routing algorithm that enables topology
agnostic deadlock-free routing within communication networks.
When computing the routing function, LASH analyzes the network topology
for the shortest-path routes between all pairs of sources /
destinations and groups these paths into virtual layers in such a way
as to avoid deadlock.
Note LASH analyzes routes and ensures deadlock freedom between switch
pairs. The link from HCA between and switch does not need virtual
layers as deadlock will not arise between switch and HCA.
In more detail, the algorithm works as follows:
1) LASH determines the shortest-path between all pairs of source /
destination switches. Note, LASH ensures the same SL is used for all
SRC/DST - DST/SRC pairs and there is no guarantee that the return path
for a given DST/SRC will be the reverse of the route SRC/DST.
2) LASH then begins an SL assignment process where a route is assigned
to a layer (SL) if the addition of that route does not cause deadlock
within that layer. This is achieved by maintaining and analysing a
channel dependency graph for each layer. Once the potential addition of
a path could lead to deadlock, LASH opens a new layer and continues the
3) Once this stage has been completed, it is highly likely that the
first layers processed will contain more paths than the latter ones.
To better balance the use of layers, LASH moves paths from one layer to
another so that the number of paths in each layer averages out.
Note, the implementation of LASH in opensm attempts to use as few
layers as possible. This number can be less than the number of actual
In general LASH is a very flexible algorithm. It can, for example,
reduce to Dimension Order Routing in certain topologies, it is topology
agnostic and fares well in the face of faults.
It has been shown that for both regular and irregular topologies, LASH
outperforms Up/Down. The reason for this is that LASH distributes the
traffic more evenly through a network, avoiding the bottleneck issues
related to a root node and always routes shortest-path.
The algorithm was developed by Simula Research Laboratory.
Use ’-R lash -Q ’ option to activate the LASH algorithm.
Note: QoS support has to be turned on in order that SL/VL mappings are
Note: LMC > 0 is not supported by the LASH routing. If this is
specified, the default routing algorithm is invoked instead.
DOR Routing Algorithm
The Dimension Order Routing algorithm is based on the Min Hop algorithm
and so uses shortest paths. Instead of spreading traffic out across
different paths with the same shortest distance, it chooses among the
available shortest paths based on an ordering of dimensions. Each port
must be consistently cabled to represent a hypercube dimension or a
mesh dimension. Paths are grown from a destination back to a source
using the lowest dimension (port) of available paths at each step.
This provides the ordering necessary to avoid deadlock. When there are
multiple links between any two switches, they still represent only one
dimension and traffic is balanced across them unless port equalization
is turned off. In the case of hypercubes, the same port must be used
throughout the fabric to represent the hypercube dimension and match on
both ends of the cable. In the case of meshes, the dimension should
consistently use the same pair of ports, one port on one end of the
cable, and the other port on the other end, continuing along the mesh
Use ’-R dor’ option to activate the DOR algorithm.
To learn more about deadlock-free routing, see the article "Deadlock
Free Message Routing in Multiprocessor Interconnection Networks" by
William J Dally and Charles L Seitz (1985).
To learn more about the up/down algorithm, see the article "Effective
Strategy to Compute Forwarding Tables for InfiniBand Networks" by Jose
Carlos Sancho, Antonio Robles, and Jose Duato at the Universidad
Politecnica de Valencia.
To learn more about LASH and the flexibility behind it, the requirement
for layers, performance comparisons to other algorithms, see the
"Layered Routing in Irregular Networks", Lysne et al, IEEE Transactions
on Parallel and Distributed Systems, VOL.16, No12, December 2005.
"Routing for the ASI Fabric Manager", Solheim et al. IEEE
Communications Magazine, Vol.44, No.7, July 2006.
"Layered Shortest Path (LASH) Routing in Irregular System Area
Networks", Skeie et al. IEEE Computer Society Communication
Architecture for Clusters 2002.
Modular Routine Engine
Modular routing engine structure allows for the ease of "plugging" new
Currently, only unicast callbacks are supported. Multicast can be added
One existing routing module is up-down "updn", which may be activated
with ’-R updn’ option (instead of old ’-u’).
General usage is: $ opensm -R ’module-name’
There is also a trivial routing module which is able to load LFT tables
from a file.
- this will load switch LFTs and/or LID matrices (min hops tables)
- this will load switch LFTs according to the path entries introduced
in the file
- no additional checks will be performed (such as "is port connected",
- in case when fabric LIDs were changed this will try to reconstruct
LFTs correctly if endport GUIDs are represented in the file
(in order to disable this, GUIDs may be removed from the file
The file format is compatible with output of ’ibroute’ util and for
whole fabric can be generated with dump_lfts.sh script.
To activate file based routing module, use:
opensm -R file -U /path/to/lfts_file
If the lfts_file is not found or is in error, the default routing
algorithm is utilized.
The ability to dump switch lid matrices (aka min hops tables) to file
and later to load these is also supported.
The usage is similar to unicast forwarding tables loading from a lfts
file (introduced by ’file’ routing engine), but new lid matrix file
name should be specified by -M or --lid_matrix_file option. For
opensm -R file -M ./opensm-lid-matrix.dump
The dump file is named ´opensm-lid-matrix.dump´ and will be generated
in standard opensm dump directory (/var/log by default) when
OSM_LOG_ROUTING logging flag is set.
When routing engine ’file’ is activated, but the lfts file is not
specified or not cannot be open default lid matrix algorithm will be
There is also a switch forwarding tables dumper which generates a file
compatible with dump_lfts.sh output. This file can be used as input for
forwarding tables loading by ’file’ routing engine. Both or one of
options -U and -M can be specified together with ´-R file´.
default OpenSM config file.
default node name map file. See ibnetdiscover for more
information on format.
default partition config file
default QOS policy config file
default prefix routes file.