NAME

The Sockets Fabric Provider

OVERVIEW

The sockets provider is a general purpose provider that can be used on any system that supports TCP sockets. The provider is not intended to provide performance improvements over regular TCP sockets, but rather to allow developers to write, test, and debug application code even on platforms that do not have high-performance fabric hardware. The sockets provider supports all libfabric provider requirements and interfaces.

SUPPORTED FEATURES

The sockets provider supports all the features defined for the libfabric API. Key features include:

Endpoint types: The provider supports all endpoint types: FI_EP_MSG, FI_EP_RDM, and FI_EP_DGRAM.
Endpoint capabilities: The following data transfer interface is supported for a all endpoint types: fi_msg. Additionally, these interfaces are supported for reliable endpoints (FI_EP_MSG and FI_EP_RDM): fi_tagged, fi_atomic, and fi_rma.
Modes: The sockets provider supports all operational modes including FI_CONTEXT and FI_MSG_PREFIX.
Progress: Sockets provider supports both FI_PROGRESS_AUTO and FI_PROGRESS_MANUAL, with a default set to auto. When progress is set to auto, a background thread runs to ensure that progress is made for asynchronous requests.

LIMITATIONS

Sockets provider attempts to emulate the entire API set, including all defined options. In order to support development on a wide range of systems, it is implemented over TCP sockets. As a result, the performance numbers are lower compared to other providers implemented over high-speed fabric, and lower than what an application might see implementing to sockets directly.

Does not support FI_ADDR_STR address format.

RUNTIME PARAMETERS

The sockets provider checks for the following environment variables -

FI_SOCKETS_PE_WAITTIME: An integer value that specifies how many milliseconds to spin while waiting for progress in FI_PROGRESS_AUTO mode.
FI_SOCKETS_MAX_CONN_RETRY: An integer value that specifies the number of socket connection retries before reporting as failure.
FI_SOCKETS_DEF_CONN_MAP_SZ: An integer to specify the default connection map size.
FI_SOCKETS_DEF_AV_SZ: An integer to specify the default address vector size.
FI_SOCKETS_DEF_CQ_SZ: An integer to specify the default completion queue size.
FI_SOCKETS_DEF_EQ_SZ: An integer to specify the default event queue size.
FI_SOCKETS_DGRAM_DROP_RATE: An integer value to specify the drop rate of dgram frame when endpoint is FI_EP_DGRAM. This is for debugging purpose only.
FI_SOCKETS_PE_AFFINITY: If specified, progress thread is bound to the indicated range(s) of Linux virtual processor ID(s). This option is currently not supported on OS X. The usage is - id_start[-id_end[:stride]][,].

LARGE SCALE JOBS

For large scale runs one can use these environment variables to set the default parameters e.g. size of the address vector(AV), completion queue (CQ), connection map etc. that satisfies the requriment of the particular benchmark. The recommended parameters for large scale runs are FI_SOCKETS_MAX_CONN_RETRY, FI_SOCKETS_DEF_CONN_MAP_SZ, FI_SOCKETS_DEF_AV_SZ, FI_SOCKETS_DEF_CQ_SZ, FI_SOCKETS_DEF_EQ_SZ.