Tribblix: manual page: dat_srq

DAT_SRQ_CREATE(3DAT) Direct Access Transport Library Functions

NAME

dat_srq_create - create an instance of a shared receive queue

SYNOPSIS

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

DAT_RETURN
dat_srq_create (
IN DAT_IA_HANDLE ia_handle,
IN DAT_PZ_HANDLE pz_handle,
IN DAT_SRQ_ATTR *srq_attr,
OUT DAT_SRQ_HANDLE *srq_handle
)

PARAMETERS

ia_handle
A handle for an open instance of the IA to which the
created SRQ belongs.

pz_handle
A handle for an instance of the Protection Zone.

srq_attr
A pointer to a structure that contains Consumer-
requested SRQ attributes.

srq_handle
A handle for the created instance of a Shared Receive
Queue.

DESCRIPTION

The dat_srq_create() function creates an instance of a Shared Receive
Queue (SRQ) that is provided to the Consumer as srq_handle. If the
value of DAT_RETURN is not DAT_SUCCESS, the value of srq_handle is
not defined.

The created SRQ is unattached to any Endpoints.

The Protection Zone pz_handle allows Consumers to control what local
memory can be used for the Recv DTO buffers posted to the SRQ. Only
memory referred to by LMRs of the posted Recv buffers that match the
SRQ Protection Zone can be accessed by the SRQ.

The srq_attributes argument specifies the initial attributes of the
created SRQ. If the operation is successful, the created SRQ will
have the queue size at least max_recv_dtos and the number of entries
on the posted Recv scatter list of at lease max_recv_iov. The created
SRQ can have the queue size and support number of entries on post
Recv buffers larger than requested. Consumer can query SRQ to find
out the actual supported queue size and maximum Recv IOV.

The Consumer must set low_watermark to DAT_SRQ_LW_DEFAULT to ensure
that an asynchronous event will not be generated immediately, since
there are no buffers in the created SRQ. The Consumer should set the
Maximum Receive DTO attribute and the Maximum number of elements in
IOV for posted buffers as needed.

When an associated EP tries to get a buffer from SRQ and there are no
buffers available, the behavior of the EP is the same as when there
are no buffers on the EP Recv Work Queue.

RETURN VALUES

DAT_SUCCESS
The operation was successful.

DAT_INSUFFICIENT_RESOURCES
The operation failed due to resource
limitations.

DAT_INVALID_HANDLE
Either ia_handle or pz_handle is an
invalid DAT handle.

DAT_INVALID_PARAMETER
One of the parameters is invalid.
Either one of the requested SRQ
attributes was invalid or a combination
of attributes is invalid.

DAT_MODEL_NOT_SUPPORTED
The requested Model was not supported
by the Provider.

USAGE

SRQ is created by the Consumer prior to creation of the EPs that will
be using it. Some Providers might restrict whether multiple EPs that
share a SRQ can have different Protection Zones. Check the
srq_ep_pz_difference_support Provider attribute. The EPs that use SRQ
might or might not use the same recv_evd.

Since a Recv buffer of SRQ can be used by any EP that is using SRQ,
the Consumer should ensure that the posted Recv buffers are large
enough to receive an incoming message on any of the EPs.

If Consumers do not want to receive an asynchronous event when the
number of buffers in SRQ falls below the Low Watermark, they should
leave its value as DAT_SRQ_LW_DEFAULT. If Consumers do want to
receive a notification, they can set the value to the desired one by
calling dat_srq_set_lw(3DAT).

SRQ allows the Consumer to use fewer Recv buffers then posting the
maximum number of buffers for each connection. If the Consumer can
upper bound the number of incoming messages over all connections
whose local EP is using SRQ, then instead of posting this maximum for
each connection the Consumer can post them for all connections on
SRQ. For example, the maximum utilized link bandwidth divided over
the message size can be used for an upper bound.

Depending on the underlying Transport, one or more messages can
arrive simultaneously on an EP that is using SRQ. Thus, the same EP
can have multiple Recv buffers in its possession without these
buffers being on SRQ or recv_evd.

Since Recv buffers can be used by multiple connections of the local
EPs that are using SRQ, the completion order of the Recv buffers is
no longer guaranteed even when they use of the same recv_evd. For
each connection the Recv buffers completion order is guaranteed to be
in the order of the posted matching Sends to the other end of the
connection. There is no ordering guarantee that Receive buffers will
be returned in the order they were posted even if there is only a
single connection (Endpoint) associated with the SRQ. There is no
ordering guarantee between different connections or between different
recv_evds.

ATTRIBUTES