fi_psm(7) @VERSION@ fi_psm(7)NAMEfi_psm - The PSM Fabric Provider
OVERVIEW
The psm provider runs over the PSM 1.x interface that is currently sup‐
ported by the Intel TrueScale Fabric. PSM provides tag-matching mes‐
sage queue functions that are optimized for MPI implementations. PSM
also has limited Active Message support, which is not officially pub‐
lished 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 lib‐
fabric 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 overlap‐
ping 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 capabili‐
ties. 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 applica‐
tion purely depends on the provider to make auto progress.
Unsupported features : These features are unsupported: connection man‐
agement, 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 nor‐
mally. 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 pro‐
cesses 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 sepa‐
rate 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 trans‐
fers 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 end‐
points. 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.
SEE ALSOfabric(7), fi_provider(7), fi_psm2(7),
AUTHORS
OpenFabrics.
Libfabric Programmer's Manual 2016-02-28 fi_psm(7)