man pages section 3: Extended Library Functions, Volume 1

Exit Print View

Updated: July 2014
 
 

dat_lmr_sync_rdma_read(3DAT)

Name

dat_lmr_sync_rdma_read - synchronize local memory with RDMA read on non-coherent memory

Synopsis

cc [ flag… ] file–ldat [ library… ] 
#include <dat/udat.h>

DAT_RETURN
    dat_lmr_sync_rdma_read (
    IN DAT_IA_HANDLE ia_handle,
    IN const DAT_LMR_TRIPLET *local_segments,
    IN DAT_VLEN num_segments
    )

Parameters

ia_handle

A handle for an open instance of the IA.

local_segments

An array of buffer segments.

num_segments

The number of segments in the local_segments argument.

Description

The dat_lmr_sync_rdma_read() function makes memory changes visible to an incoming RDMA Read operation. This operation guarantees consistency by locally flushing the non-coherent cache prior to it being retrieved by remote peer RDMA read operations.

The dat_lmr_sync_rdma_read() function is needed if and only if the Provider attribute specifies that this operation is needed prior to an incoming RDMA Read operation. The Consumer must call dat_lmr_sync_rdma_read() after modifying data in a memory range in this region that will be the target of an incoming RDMA Read operation. The dat_lmr_sync_rdma_read() function must be called after the Consumer has modified the memory range but before the RDMA Read operation begins. The memory range that will be accessed by the RDMA read operation must be supplied by the caller in the local_segments array. After this call returns, the RDMA Read operation can safely see the modified contents of the memory range. It is permissible to batch synchronizations for multiple RDMA Read operations in a single call by passing a local_segments array that includes all modified memory ranges. The local_segments entries need not contain the same LMR and need not be in the same Protection Zone.

If the Provider attribute specifying that this operation is required attempts to read from a memory range that is not properly synchronized using dat_lmr_sync_rdma_read(), the returned contents are undefined.

Return Values

DAT_SUCCESS

The operation was successful.

DAT_INVALID_HANDLE

The DAT handle is invalid.

DAT_INVALID_PARAMETER

One of the parameters is invalid. For example, the address range for a local segment fell outside the boundaries of the corresponding Local Memory Region or the LMR handle was invalid.

Usage

Determining when an RDMA Read will start and what memory range it will read is the Consumer's responsibility. One possibility is to have the Consumer that is modifying memory call dat_lmr_sync_rdma_read() and then post a Send DTO message that identifies the range in the body of the Send. The Consumer wanting to perform the RDMA Read can receive this message and know when it is safe to initiate the RDMA Read operation.

This call ensures that the Provider receives a coherent view of the buffer contents upon a subsequent remote RDMA Read operation. After the call completes, the Consumer can be assured that all platform-specific buffer and cache updates have been performed, and that the LMR range has consistency with the Provider hardware. Any subsequent write by the Consumer can void this consistency. The Provider is not required to detect such access.

The action performed on the cache before the RDMA Read depends on the cache type:

  • I/O noncoherent cache will be invalidated.

  • CPU noncoherent cache will be flushed.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
Unsafe
Standard
uDAPL, 1.2

See Also

dat_lmr_sync_rdma_write(3DAT), libdat(3LIB) , attributes(5)