fi_rxm(7) Libfabric Programmer's Manual
fi_rxm - The RxM (RDM over MSG) Utility Provider
The RxM provider (ofi_rxm) is an utility provider that supports RDM endpoint emulated over MSG endpoint of a core provider.
RxM provider requires the core provider to support the following features:
MSG endpoints (FI_EP_MSG)
RMA read/write (FI_RMA)
FI_OPT_CM_DATA_SIZE of at least 24 bytes
The RxM provider currently supports FI_MSG, FI_TAGGED and FI_RMA capabilities.
- Endpoint types
- The provider supports only FI_EP_RDM.
- Endpoint capabilities
- The following data transfer interface is supported: FI_MSG, FI_TAGGED, FI_RMA.
- The RxM provider supports FI_PROGRESS_AUTO.
- Addressing Formats
- FI_SOCKADDR, FI_SOCKADDR_IN
- Memory Region
- FI_MR_VIRT_ADDR, FI_MR_ALLOCATED, FI_MR_PROV_KEY MR mode bits would be required from the app in case the core provider requires it.
When using RxM provider, some limitations from the underlying MSG provider could also show up. Please refer to the corresponding MSG provider man pages to find about those limitations.
RxM provider does not support the following features:
Application error data buffers
Reporting unknown source addr data as part of completions
When sending large messages, an app doing an sread or waiting on the CQ file descriptor may not get a completion when reading the CQ after being woken up from the wait. The app has to do sread or wait on the file descriptor again.
The ofi_rxm provider checks for the following environment variables.
- Defines the transmit buffer size / inject size. Messages of size less than this would be transmitted via an eager protocol and those above would be transmitted via a rendezvous protocol. Transmit data would be copied up to this size (default: ~16k).
- Defines the maximum number of MSG provider CQ entries (default: 1) that would be read per progress (RxM CQ read).
- Defines default TX context size (default: 1024)
- Defines default RX context size (default: 1024)
- Defines FI_EP_MSG TX size that would be requested (default: 128).
- Defines FI_EP_MSG RX size that would be requested (default: 128).
- Defines the expected number of ranks / peers an endpoint would communicate with (default: 256).
To optimize for bandwidth, ensure you use higher values than default for FI_OFI_RXM_TX_SIZE, FI_OFI_RXM_RX_SIZE, FI_OFI_RXM_MSG_TX_SIZE, FI_OFI_RXM_MSG_RX_SIZE subject to memory limits of the system and the tx and rx sizes supported by the MSG provider.
To conserve memory, ensure FI_UNIVERSE_SIZE set to what is required. Similarly check that FI_OFI_RXM_TX_SIZE, FI_OFI_RXM_RX_SIZE, FI_OFI_RXM_MSG_TX_SIZE and FI_OFI_RXM_MSG_RX_SIZE env variables are set to only required values.