Ubuntu Manpage: fi_psm - The PSM Fabric Provider

NAME

       fi_psm - The PSM Fabric Provider

OVERVIEW

       The  psm provider runs over the PSM 1.x interface that is currently supported by the Intel
       TrueScale Fabric.  PSM provides tag-matching message queue functions  that  are  optimized
       for  MPI  implementations.   PSM  also  has  limited  Active Message support, which is not
       officially published but is quite stable and well documented in the source code  (part  of
       the  OFED  release).   The  psm  provider makes use of both the tag-matching message queue
       functions and the Active Message functions to support a variety of libfabric data transfer
       APIs, including tagged message queue, message queue, RMA, and atomic operations.

       The  psm provider can work with the psm2-compat library, which exposes a PSM 1.x interface
       over the Intel Omni-Path Fabric.

LIMITATIONS

       The psm provider doesn't support all the features defined in the libfabric API.  Here  are
       some of the limitations:

       Endpoint types : Only support non-connection based types FI_DGRAM and FI_RDM

       Endpoint   capabilities   :  Endpoints  can  support  any  combination  of  data  transfer
       capabilities FI_TAGGED, FI_MSG, FI_ATOMICS, and FI_RMA.  These capabilities can be further
       refined  by  FI_SEND,  FI_RECV,  FI_READ, FI_WRITE, FI_REMOTE_READ, and FI_REMOTE_WRITE to
       limit the direction of operations.  The limitation is  that  no  two  endpoints  can  have
       overlapping  receive  or  RMA  target  capabilities  in  any of the above categories.  For
       example it is fine to have two endpoints with  FI_TAGGED  |  FI_SEND,  one  endpoint  with
       FI_TAGGED | FI_RECV, one endpoint with FI_MSG, one endpoint with FI_RMA | FI_ATOMICS.  But
       it is not allowed to have two endpoints with FI_TAGGED, or two endpoints with FI_RMA.

       FI_MULTI_RECV is supported for non-tagged message queue only.

       Other supported capabilities include FI_TRIGGER.

       Modes : FI_CONTEXT is required for the FI_TAGGED and FI_MSG capabilities.  That means, any
       request  belonging  to  these  two categories that generates a completion must pass as the
       operation context a valid pointer to type struct fi_context, and the space  referenced  by
       the  pointer  must remain untouched until the request has completed.  If none of FI_TAGGED
       and FI_MSG is asked for, the FI_CONTEXT mode is not required.

       Progress : The psm provider requires manual progress.  The application is expected to call
       fi_cq_read  or fi_cntr_read function from time to time when no other libfabric function is
       called to ensure progress is made in a timely manner.   The  provider  does  support  auto
       progress  mode.  However, the performance can be significantly impacted if the application
       purely depends on the provider to make auto progress.

       Unsupported features : These features are  unsupported:  connection  management,  scalable
       endpoint, passive endpoint, shared receive context, send/inject with immediate data.

RUNTIME PARAMETERS

The psm provider checks for the following environment variables:

FI_PSM_UUID : PSM requires that each job has a unique ID (UUID). All the processes in the
same job need to use the same UUID in order to be able to talk to each other. The PSM
reference manual advises to keep UUID unique to each job. In practice, it generally works
fine to reuse UUID as long as (1) no two jobs with the same UUID are running at the same
time; and (2) previous jobs with the same UUID have exited normally. If running into
"resource busy" or "connection failure" issues with unknown reason, it is advisable to
manually set the UUID to a value different from the default.

The default UUID is 0FFF0FFF-0000-0000-0000-0FFF0FFF0FFF.

FI_PSM_NAME_SERVER : The psm provider has a simple built-in name server that can be used
to resolve an IP address or host name into a transport address needed by the fi_av_insert
call. The main purpose of this name server is to allow simple client-server type
applications (such as those in fabtest) to be written purely with libfabric, without using
any out-of-band communication mechanism. For such applications, the server would run
first, and the client would call fi_getinfo with the node parameter set to the IP address
or host name of the server. The resulting fi_info structure would have the transport
address of the server in the dest_addr field.

The name server won't work properly if there are more than one processes from the same job
(i.e. with the same UUID) running on the same node and acting as servers. For such
scenario it is recommended to have each process getting local transport address with
fi_getname and exchanging the addresses with out-of-band mechanism.

The name server is on by default. It can be turned off by setting the variable to 0.
This may save a small amount of resource since a separate thread is created when the name
server is on.

The provider detects OpenMPI and MPICH runs and changes the default setting to off.

FI_PSM_TAGGED_RMA : The RMA functions are implemented on top of the PSM Active Message
functions. The Active Message functions have limit on the size of data can be transferred
in a single message. Large transfers can be divided into small chunks and be pipe-lined.
However, the bandwidth is sub-optimal by doing this way.

The psm provider use PSM tag-matching message queue functions to achieve higher bandwidth
for large size RMA. For this purpose, a bit is reserved from the tag space to separate
the RMA traffic from the regular tagged message queue.

The option is on by default. To turn it off set the variable to 0.

FI_PSM_AM_MSG : The psm provider implements the non-tagged message queue over the PSM
tag-matching message queue. One tag bit is reserved for this purpose. Alternatively, the
non-tagged message queue can be implemented over Active Message. This experimental
feature has slightly larger latency.

This option is off by default. To turn it on set the variable to 1.

FI_PSM_DELAY : Time (seconds) to sleep before closing PSM endpoints. This is a workaround
for a bug in some versions of PSM library.

The default setting is 1.

FI_PSM_TIMEOUT : Timeout (seconds) for gracefully closing PSM endpoints. A forced closing
will be issued if timeout expires.

The default setting is 5.

FI_PSM_PROG_INTERVAL : When auto progress is enabled (asked via the hints to fi_getinfo),
a progress thread is created to make progress calls from time to time. This option set
the interval (microseconds) between progress calls.

The default setting is 1 if affininty is set, or 1000 if not. See FI_PSM_PROG_AFFINITY.

FI_PSM_PROG_AFFINITY : When set, specify the set of CPU cores to set the progress thread
affinity to. The format is <start>[:<end>[:<stride>]][,<start>[:<end>[:<stride>]]]*,
where each triplet <start>:<end>:<stride> defines a block of core_ids. Both <start> and
<end> can be either the core_id (when >=0) or core_id - num_cores (when <0).

By default affinity is not set.

AUTHORS

       OpenFabrics.

NAME

OVERVIEW

LIMITATIONS

RUNTIME PARAMETERS

SEE ALSO

AUTHORS