Provided by: libfabric-dev_1.6.2-3ubuntu0.1_amd64 
NAME
fi_cq - Completion queue operations
fi_cq_open / fi_close : Open/close a completion queue
fi_control : Control CQ operation or attributes.
fi_cq_read / fi_cq_readfrom / fi_cq_readerr : Read a completion from a completion queue
fi_cq_sread / fi_cq_sreadfrom : A synchronous (blocking) read that waits until a specified condition has
been met before reading a completion from a completion queue.
fi_cq_signal : Unblock any thread waiting in fi_cq_sread or fi_cq_sreadfrom.
fi_cq_strerror : Converts provider specific error information into a printable string
SYNOPSIS
#include <rdma/fi_domain.h>
int fi_cq_open(struct fid_domain *domain, struct fi_cq_attr *attr,
struct fid_cq **cq, void *context);
int fi_close(struct fid *cq);
int fi_control(struct fid *cq, int command, void *arg);
ssize_t fi_cq_read(struct fid_cq *cq, void *buf, size_t count);
ssize_t fi_cq_readfrom(struct fid_cq *cq, void *buf, size_t count,
fi_addr_t *src_addr);
ssize_t fi_cq_readerr(struct fid_cq *cq, struct fi_cq_err_entry *buf,
uint64_t flags);
ssize_t fi_cq_sread(struct fid_cq *cq, void *buf, size_t count,
const void *cond, int timeout);
ssize_t fi_cq_sreadfrom(struct fid_cq *cq, void *buf, size_t count,
fi_addr_t *src_addr, const void *cond, int timeout);
int fi_cq_signal(struct fid_cq *cq);
const char * fi_cq_strerror(struct fid_cq *cq, int prov_errno,
const void *err_data, char *buf, size_t len);
ARGUMENTS
domain : Open resource domain
cq : Completion queue
attr : Completion queue attributes
context : User specified context associated with the completion queue.
buf : For read calls, the data buffer to write completions into. For write calls, a completion to insert
into the completion queue. For fi_cq_strerror, an optional buffer that receives printable error
information.
count : Number of CQ entries.
len : Length of data buffer
src_addr : Source address of a completed receive operation
flags : Additional flags to apply to the operation
command : Command of control operation to perform on CQ.
arg : Optional control argument
cond : Condition that must be met before a completion is generated
timeout : Time in milliseconds to wait. A negative value indicates infinite timeout.
prov_errno : Provider specific error value
err_data : Provider specific error data related to a completion
DESCRIPTION
Completion queues are used to report events associated with data transfers. They are associated with
message sends and receives, RMA, atomic, tagged messages, and triggered events. Reported events are
usually associated with a fabric endpoint, but may also refer to memory regions used as the target of an
RMA or atomic operation.
fi_cq_open
fi_cq_open allocates a new completion queue. Unlike event queues, completion queues are associated with
a resource domain and may be offloaded entirely in provider hardware.
The properties and behavior of a completion queue are defined by struct fi_cq_attr.
struct fi_cq_attr {
size_t size; /* # entries for CQ */
uint64_t flags; /* operation flags */
enum fi_cq_format format; /* completion format */
enum fi_wait_obj wait_obj; /* requested wait object */
int signaling_vector; /* interrupt affinity */
enum fi_cq_wait_cond wait_cond; /* wait condition format */
struct fid_wait *wait_set; /* optional wait set */
};
size : Specifies the minimum size of a completion queue. A value of 0 indicates that the provider may
choose a default value.
flags : Flags that control the configuration of the CQ.
• FI_AFFINITY : Indicates that the signaling_vector field (see below) is valid.
format : Completion queues allow the application to select the amount of detail that it must store and
report. The format attribute allows the application to select one of several completion formats,
indicating the structure of the data that the completion queue should return when read. Supported
formats and the structures that correspond to each are listed below. The meaning of the CQ entry fields
are defined in the Completion Fields section.
• FI_CQ_FORMAT_UNSPEC : If an unspecified format is requested, then the CQ will use a provider selected
default format.
• FI_CQ_FORMAT_CONTEXT : Provides only user specified context that was associated with the completion.
struct fi_cq_entry {
void *op_context; /* operation context */
};
• FI_CQ_FORMAT_MSG : Provides minimal data for processing completions, with expanded support for
reporting information about received messages.
struct fi_cq_msg_entry {
void *op_context; /* operation context */
uint64_t flags; /* completion flags */
size_t len; /* size of received data */
};
• FI_CQ_FORMAT_DATA : Provides data associated with a completion. Includes support for received message
length, remote CQ data, and multi-receive buffers.
struct fi_cq_data_entry {
void *op_context; /* operation context */
uint64_t flags; /* completion flags */
size_t len; /* size of received data */
void *buf; /* receive data buffer */
uint64_t data; /* completion data */
};
• FI_CQ_FORMAT_TAGGED : Expands completion data to include support for the tagged message interfaces.
struct fi_cq_tagged_entry {
void *op_context; /* operation context */
uint64_t flags; /* completion flags */
size_t len; /* size of received data */
void *buf; /* receive data buffer */
uint64_t data; /* completion data */
uint64_t tag; /* received tag */
};
wait_obj : CQ's may be associated with a specific wait object. Wait objects allow applications to block
until the wait object is signaled, indicating that a completion is available to be read. Users may use
fi_control to retrieve the underlying wait object associated with a CQ, in order to use it in other
system calls. The following values may be used to specify the type of wait object associated with a CQ:
FI_WAIT_NONE, FI_WAIT_UNSPEC, FI_WAIT_SET, FI_WAIT_FD, and FI_WAIT_MUTEX_COND. The default is
FI_WAIT_NONE.
• FI_WAIT_NONE : Used to indicate that the user will not block (wait) for completions on the CQ. When
FI_WAIT_NONE is specified, the application may not call fi_cq_sread or fi_cq_sreadfrom.
• FI_WAIT_UNSPEC : Specifies that the user will only wait on the CQ using fabric interface calls, such as
fi_cq_sread or fi_cq_sreadfrom. In this case, the underlying provider may select the most appropriate
or highest performing wait object available, including custom wait mechanisms. Applications that
select FI_WAIT_UNSPEC are not guaranteed to retrieve the underlying wait object.
• FI_WAIT_SET : Indicates that the completion queue should use a wait set object to wait for completions.
If specified, the wait_set field must reference an existing wait set object.
• FI_WAIT_FD : Indicates that the CQ should use a file descriptor as its wait mechanism. A file
descriptor wait object must be usable in select, poll, and epoll routines. However, a provider may
signal an FD wait object by marking it as readable, writable, or with an error.
• FI_WAIT_MUTEX_COND : Specifies that the CQ should use a pthread mutex and cond variable as a wait
object.
• FI_WAIT_CRITSEC_COND : Windows specific. Specifies that the CQ should use a critical section and
condition variable as a wait object.
signaling_vector : If the FI_AFFINITY flag is set, this indicates the logical cpu number (0..max cpu - 1)
that interrupts associated with the CQ should target. This field should be treated as a hint to the
provider and may be ignored if the provider does not support interrupt affinity.
wait_cond : By default, when a completion is inserted into a CQ that supports blocking reads
(fi_cq_sread/fi_cq_sreadfrom), the corresponding wait object is signaled. Users may specify a condition
that must first be met before the wait is satisfied. This field indicates how the provider should
interpret the cond field, which describes the condition needed to signal the wait object.
A wait condition should be treated as an optimization. Providers are not required to meet the
requirements of the condition before signaling the wait object. Applications should not rely on the
condition necessarily being true when a blocking read call returns.
If wait_cond is set to FI_CQ_COND_NONE, then no additional conditions are applied to the signaling of the
CQ wait object, and the insertion of any new entry will trigger the wait condition. If wait_cond is set
to FI_CQ_COND_THRESHOLD, then the cond field is interpreted as a size_t threshold value. The threshold
indicates the number of entries that are to be queued before at the CQ before the wait is satisfied.
This field is ignored if wait_obj is set to FI_WAIT_NONE.
wait_set : If wait_obj is FI_WAIT_SET, this field references a wait object to which the completion queue
should attach. When an event is inserted into the completion queue, the corresponding wait set will be
signaled if all necessary conditions are met. The use of a wait_set enables an optimized method of
waiting for events across multiple event and completion queues. This field is ignored if wait_obj is not
FI_WAIT_SET.
fi_close
The fi_close call releases all resources associated with a completion queue. Any completions which
remain on the CQ when it is closed are lost.
When closing the CQ, there must be no opened endpoints, transmit contexts, or receive contexts associated
with the CQ. If resources are still associated with the CQ when attempting to close, the call will
return -FI_EBUSY.
fi_control
The fi_control call is used to access provider or implementation specific details of the completion
queue. Access to the CQ should be serialized across all calls when fi_control is invoked, as it may
redirect the implementation of CQ operations. The following control commands are usable with a CQ.
FI_GETWAIT (void **) : This command allows the user to retrieve the low-level wait object associated with
the CQ. The format of the wait-object is specified during CQ creation, through the CQ attributes. The
fi_control arg parameter should be an address where a pointer to the returned wait object will be
written. See fi_eq.3 for addition details using fi_control with FI_GETWAIT.
fi_cq_read
The fi_cq_read operation performs a non-blocking read of completion data from the CQ. The format of the
completion event is determined using the fi_cq_format option that was specified when the CQ was opened.
Multiple completions may be retrieved from a CQ in a single call. The maximum number of entries to
return is limited to the specified count parameter, with the number of entries successfully read from the
CQ returned by the call. (See return values section below.)
CQs are optimized to report operations which have completed successfully. Operations which fail are
reported 'out of band'. Such operations are retrieved using the fi_cq_readerr function. When an
operation that has completed with an unexpected error is encountered, it is placed into a temporary error
queue. Attempting to read from a CQ while an item is in the error queue results in fi_cq_read failing
with a return code of -FI_EAVAIL. Applications may use this return code to determine when to call
fi_cq_readerr.
fi_cq_readfrom
The fi_cq_readfrom call behaves identical to fi_cq_read, with the exception that it allows the CQ to
return source address information to the user for any received data. Source address data is only
available for those endpoints configured with FI_SOURCE capability. If fi_cq_readfrom is called on an
endpoint for which source addressing data is not available, the source address will be set to
FI_ADDR_NOTAVAIL. The number of input src_addr entries must be the same as the count parameter.
Returned source addressing data is converted from the native address used by the underlying fabric into
an fi_addr_t, which may be used in transmit operations. Typically, returning fi_addr_t requires that the
source address be inserted into the address vector associated with the receiving endpoint. For endpoints
allocated using the FI_SOURCE_ERR capability, if the source address has not been inserted into the
address vector, fi_cq_readfrom will return -FI_EAVAIL. The completion will then be reported through
fi_cq_readerr with error code -FI_EADDRNOTAVAIL. See fi_cq_readerr for details.
If FI_SOURCE is specified without FI_SOURCE_ERR, source addresses which cannot be mapped to a local
fi_addr_t will be reported as FI_ADDR_NOTAVAIL. The behavior is dependent on the type of address vector
in use. For AVs of type FI_AV_MAP, source addresses may be mapped directly to an fi_addr_t value, even
if the source address were not inserted into the AV. This allows the provider to optimize the reporting
of the source fi_addr_t without the overhead of verifying whether the address is in the AV. If full
address validation is necessary, FI_SOURCE_ERR must be used.
fi_cq_sread / fi_cq_sreadfrom
The fi_cq_sread and fi_cq_sreadfrom calls are the blocking equivalent operations to fi_cq_read and
fi_cq_readfrom. Their behavior is similar to the non-blocking calls, with the exception that the calls
will not return until either a completion has been read from the CQ or an error or timeout occurs.
It is invalid for applications to call these functions if the CQ has been configured with a wait object
of FI_WAIT_NONE or FI_WAIT_SET.
fi_cq_readerr
The read error function, fi_cq_readerr, retrieves information regarding any asynchronous operation which
has completed with an unexpected error. fi_cq_readerr is a non-blocking call, returning immediately
whether an error completion was found or not.
Error information is reported to the user through struct fi_cq_err_entry. The format of this structure
is defined below.
struct fi_cq_err_entry {
void *op_context; /* operation context */
uint64_t flags; /* completion flags */
size_t len; /* size of received data */
void *buf; /* receive data buffer */
uint64_t data; /* completion data */
uint64_t tag; /* message tag */
size_t olen; /* overflow length */
int err; /* positive error code */
int prov_errno; /* provider error code */
void *err_data; /* error data */
size_t err_data_size; /* size of err_data */
};
The general reason for the error is provided through the err field. Provider specific error information
may also be available through the prov_errno and err_data fields. Users may call fi_cq_strerror to
convert provider specific error information into a printable string for debugging purposes. See field
details below for more information on the use of err_data and err_data_size.
Notable completion error codes are given below.
FI_EADDRNOTAVAIL : This error code is used by CQs configured with FI_SOURCE_ERR to report completions for
which a matching fi_addr_t source address could not be found. An error code of FI_EADDRNOTAVAIL
indicates that the data transfer was successfully received and processed, with the fi_cq_err_entry fields
containing information about the completion. The err_data field will be set to the source address data.
The source address will be in the same format as specified through the fi_info addr_format field for the
opened domain. This may be passed directly into an fi_av_insert call to add the source address to the
address vector.
fi_cq_signal
The fi_cq_signal call will unblock any thread waiting in fi_cq_sread or fi_cq_sreadfrom. This may be
used to wake-up a thread that is blocked waiting to read a completion operation. The fi_cq_signal
operation is only available if the CQ was configured with a wait object.
COMPLETION FIELDS
The CQ entry data structures share many of the same fields. The meanings of these fields are the same
for all CQ entry structure formats.
op_context : The operation context is the application specified context value that was provided with an
asynchronous operation. The op_context field is valid for all completions that are associated with an
asynchronous operation.
For completion events that are not associated with a posted operation, this field will be set to NULL.
This includes completions generated at the target in response to RMA write operations that carry CQ data
(FI_REMOTE_WRITE | FI_REMOTE_CQ_DATA flags set), when the FI_RX_CQ_DATA mode bit is not required.
flags : This specifies flags associated with the completed operation. The Completion Flags section below
lists valid flag values. Flags are set for all relevant completions.
len : This len field only applies to completed receive operations (e.g. fi_recv, fi_trecv, etc.). It
indicates the size of received message data -- i.e. how many data bytes were placed into the associated
receive buffer by a corresponding fi_send/fi_tsend/et al call. If an endpoint has been configured with
the FI_MSG_PREFIX mode, the len also reflects the size of the prefix buffer.
buf : The buf field is only valid for completed receive operations, and only applies when the receive
buffer was posted with the FI_MULTI_RECV flag. In this case, buf points to the starting location where
the receive data was placed.
data : The data field is only valid if the FI_REMOTE_CQ_DATA completion flag is set, and only applies to
receive completions. If FI_REMOTE_CQ_DATA is set, this field will contain the completion data provided
by the peer as part of their transmit request. The completion data will be given in host byte order.
tag : A tag applies only to received messages that occur using the tagged interfaces. This field
contains the tag that was included with the received message. The tag will be in host byte order.
olen : The olen field applies to received messages. It is used to indicate that a received message has
overrun the available buffer space and has been truncated. The olen specifies the amount of data that
did not fit into the available receive buffer and was discarded.
err : This err code is a positive fabric errno associated with a completion. The err value indicates the
general reason for an error, if one occurred. See fi_errno.3 for a list of possible error codes.
prov_errno : On an error, prov_errno may contain a provider specific error code. The use of this field
and its meaning is provider specific. It is intended to be used as a debugging aid. See fi_cq_strerror
for additional details on converting this error value into a human readable string.
err_data : On an error, err_data may reference a provider specific amount of data associated with an
error. The use of this field and its meaning is provider specific. It is intended to be used as a
debugging aid. See fi_cq_strerror for additional details on converting this error data into a human
readable string.
err_data_size : On input, err_data_size indicates the size of the err_data buffer in bytes. On output,
err_data_size will be set to the number of bytes copied to the err_data buffer. The err_data information
is typically used with fi_cq_strerror to provide details about the type of error that occurred.
For compatibility purposes, if err_data_size is 0 on input, or the fabric was opened with release < 1.5,
err_data will be set to a data buffer owned by the provider. The contents of the buffer will remain
valid until a subsequent read call against the CQ. Applications must serialize access to the CQ when
processing errors to ensure that the buffer referenced by err_data does not change.
COMPLETION FLAGS
Completion flags provide additional details regarding the completed operation. The following completion
flags are defined.
FI_SEND : Indicates that the completion was for a send operation. This flag may be combined with an
FI_MSG or FI_TAGGED flag.
FI_RECV : Indicates that the completion was for a receive operation. This flag may be combined with an
FI_MSG or FI_TAGGED flag.
FI_RMA : Indicates that an RMA operation completed. This flag may be combined with an FI_READ, FI_WRITE,
FI_REMOTE_READ, or FI_REMOTE_WRITE flag.
FI_ATOMIC : Indicates that an atomic operation completed. This flag may be combined with an FI_READ,
FI_WRITE, FI_REMOTE_READ, or FI_REMOTE_WRITE flag.
FI_MSG : Indicates that a message-based operation completed. This flag may be combined with an FI_SEND
or FI_RECV flag.
FI_TAGGED : Indicates that a tagged message operation completed. This flag may be combined with an
FI_SEND or FI_RECV flag.
FI_MULTICAST : Indicates that a multicast operation completed. This flag may be combined with FI_MSG and
relevant flags. This flag is only guaranteed to be valid for received messages if the endpoint has been
configured with FI_SOURCE.
FI_READ : Indicates that a locally initiated RMA or atomic read operation has completed. This flag may
be combined with an FI_RMA or FI_ATOMIC flag.
FI_WRITE : Indicates that a locally initiated RMA or atomic write operation has completed. This flag may
be combined with an FI_RMA or FI_ATOMIC flag.
FI_REMOTE_READ : Indicates that a remotely initiated RMA or atomic read operation has completed. This
flag may be combined with an FI_RMA or FI_ATOMIC flag.
FI_REMOTE_WRITE : Indicates that a remotely initiated RMA or atomic write operation has completed. This
flag may be combined with an FI_RMA or FI_ATOMIC flag.
FI_REMOTE_CQ_DATA : This indicates that remote CQ data is available as part of the completion.
FI_MULTI_RECV : This flag applies to receive buffers that were posted with the FI_MULTI_RECV flag set.
This completion flag indicates that the original receive buffer referenced by the completion has been
consumed and was released by the provider. Providers may set this flag on the last message that is
received into the multi- recv buffer, or may generate a separate completion that indicates that the
buffer has been released.
Applications can distinguish between these two cases by examining the completion entry flags field. If
additional flags, such as FI_RECV, are set, the completion is associated with a received message. In
this case, the buf field will reference the location where the received message was placed into the
multi-recv buffer. Other fields in the completion entry will be determined based on the received
message. If other flag bits are zero, the provider is reporting that the multi-recv buffer has been
released, and the completion entry is not associated with a received message.
NOTES
A completion queue must be bound to at least one enabled endpoint before any operation such as
fi_cq_read, fi_cq_readfrom, fi_cq_sread, fi_cq_sreadfrom etc. can be called on it.
Completion flags may be suppressed if the FI_NOTIFY_FLAGS_ONLY mode bit has been set. When enabled, only
the following flags are guaranteed to be set in completion data when they are valid: FI_REMOTE_READ and
FI_REMOTE_WRITE (when FI_RMA_EVENT capability bit has been set), FI_REMOTE_CQ_DATA, and FI_MULTI_RECV.
If a completion queue has been overrun, it will be placed into an 'overrun' state. Read operations will
continue to return any valid, non-corrupted completions, if available. After all valid completions have
been retrieved, any attempt to read the CQ will result in it returning an FI_EOVERRUN error event.
Overrun completion queues are considered fatal and may not be used to report additional completions once
the overrun occurs.
RETURN VALUES
fi_cq_open / fi_cq_signal : Returns 0 on success. On error, a negative value corresponding to fabric
errno is returned.
fi_cq_read / fi_cq_readfrom / fi_cq_readerr fi_cq_sread / fi_cq_sreadfrom : On success, returns the
number of completion events retrieved from the completion queue. On error, a negative value
corresponding to fabric errno is returned. If no completions are available to return from the CQ,
-FI_EAGAIN will be returned.
fi_cq_strerror : Returns a character string interpretation of the provider specific error returned with a
completion.
Fabric errno values are defined in rdma/fi_errno.h.
SEE ALSO
fi_getinfo(3), fi_endpoint(3), fi_domain(3), fi_eq(3), fi_cntr(3), fi_poll(3)
AUTHORS
OpenFabrics.
Libfabric Programmer's Manual 2017-12-06 fi_cq(3)