NAME

fi_rstream - The Rstream Fabric Provider

OVERVIEW

The rstream provider supports stream messaging over message based RMA. It maps stream to message over a core RMA-based OFI provider. Only Endpoints and EQs are needed for connection start-up and messaging. Unlike other OFI providers, rstream does not support CQs or memory registration of any kind. In order to asynchronously wait for a completion (cm/msg), one can use fi_control on the endpoint/eq to get an fd to use in a poll call. For messaging completions, use FI_PEEK on send/recv after poll to see what type of transaction has transpired.

SUPPORTED FEATURES

The rstream provider currently supports FI_MSG capabilities.

Endpoint types: The provider supports only endpoint type FI_EP_SOCK_STREAM.

Endpoint capabilities : The following data transfer interface is supported: fi_msg.

Modes: The provider does not require the use of any mode bits but supports core providers that require FI_CONTEXT and FI_RX_CQ_DATA.
Progress: The rstream provider only supports FI_PROGRESS_MANUAL.
Threading Model: The provider supports FI_THREAD_SAFE
Verbs-iWarp: The provider has added features to enable iWarp. To use this feature, the ep protocol iWarp must be requested in an fi_getinfo call.

LIMITATIONS

The rstream provider is experimental and lacks performance validation and extensive testing. The iWarp protocol may need extra initialization work to re-enable. Currently the rstream provider is used to by the rsockets-OFI library as a ULP and hooks into the core provider verbs. It is not interoperable with the previous rsockets(v1) protocol. There are default settings that limit the message stream (provider memory region size and CQ size). These can be modified by fi_setopt.

SETTINGS

The rstream provider settings can be modified via fi_setopt on the endpoint (FI_OPT_ENDPOINT) along with the following parameters:

FI_OPT_SEND_BUF_SIZE: Size of the send buffer. Default is 32KB.
FI_OPT_RECV_BUF_SIZE: Size of the recv buffer. Default is 32KB.
FI_OPT_TX_SIZE: Size of the send queue. Default is 384.
FI_OPT_RX_SIZE: Size of the recv queue. Default is 384.

OFI EXTENSIONS

The rstream provider has extended the current OFI API set in order to enable a user implementation of Poll. Specifically sendmsg(FI_PEEK) is supported which replicates the behavior of the recvmsg(FI_PEEK) feature.

AUTHORS

OpenFabrics.

2022-12-11

Libfabric Programmer’s Manual