Ubuntu Manpage: fi_cntr - Completion and event counter operations

Provided by: libfabric-dev_1.17.0-3_amd64

NAME

       fi_cntr - Completion and event counter operations

       fi_cntr_open / fi_close
              Allocate/free a counter

       fi_cntr_read
              Read the current value of a counter

       fi_cntr_readerr
              Reads the number of operations which have completed in error.

       fi_cntr_add
              Increment a counter by a specified value

       fi_cntr_set
              Set a counter to a specified value

       fi_cntr_wait
              Wait for a counter to be greater or equal to a threshold value

SYNOPSIS

              #include <rdma/fi_domain.h>

              int fi_cntr_open(struct fid_domain *domain, struct fi_cntr_attr *attr,
                  struct fid_cntr **cntr, void *context);

              int fi_close(struct fid *cntr);

              uint64_t fi_cntr_read(struct fid_cntr *cntr);

              uint64_t fi_cntr_readerr(struct fid_cntr *cntr);

              int fi_cntr_add(struct fid_cntr *cntr, uint64_t value);

              int fi_cntr_adderr(struct fid_cntr *cntr, uint64_t value);

              int fi_cntr_set(struct fid_cntr *cntr, uint64_t value);

              int fi_cntr_seterr(struct fid_cntr *cntr, uint64_t value);

              int fi_cntr_wait(struct fid_cntr *cntr, uint64_t threshold,
                  int timeout);

ARGUMENTS

       domain Fabric domain

       cntr   Fabric counter

       attr   Counter attributes

       context
              User specified context associated with the counter

       value  Value to increment or set counter

       threshold
              Value to compare counter against

       timeout
              Time in milliseconds to wait.  A negative value indicates infinite timeout.

DESCRIPTION

Counters record the number of requested operations that have completed. Counters can
provide a light-weight completion mechanism by allowing the suppression of CQ completion
entries. They are useful for applications that only need to know the number of requests
that have completed, and not details about each request. For example, counters may be
useful for implementing credit based flow control or tracking the number of remote
processes that have responded to a request.

Counters typically only count successful completions. However, if an operation completes
in error, it may increment an associated error value. That is, a counter actually stores
two distinct values, with error completions updating an error specific value.

Counters are updated following the completion event semantics defined in fi_cq(3). The
timing of the update is based on the type of transfer and any specified operation flags.

fi_cntr_open
fi_cntr_open allocates a new fabric counter. The properties and behavior of the counter
are defined by struct fi_cntr_attr.

struct fi_cntr_attr {
enum fi_cntr_events events; /* type of events to count */
enum fi_wait_obj wait_obj; /* requested wait object */
struct fid_wait *wait_set; /* optional wait set */
uint64_t flags; /* operation flags */
};

events A counter captures different types of events. The specific type which is to
counted are one of the following:

- FI_CNTR_EVENTS_COMP
The counter increments for every successful completion that occurs on an associated
bound endpoint. The type of completions – sends and/or receives – which are
counted may be restricted using control flags when binding the counter and the
endpoint. Counters increment on all successful completions, separately from
whether the operation generates an entry in an event queue.

wait_obj
Counters may be associated with a specific wait object. Wait objects allow
applications to block until the wait object is signaled, indicating that a counter
has reached a specific threshold. Users may use fi_control to retrieve the
underlying wait object associated with a counter, 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 counter: FI_WAIT_NONE, FI_WAIT_UNSPEC, FI_WAIT_SET, FI_WAIT_FD,
FI_WAIT_MUTEX_COND, and FI_WAIT_YIELD. The default is FI_WAIT_NONE.

- FI_WAIT_NONE
Used to indicate that the user will not block (wait) for events on the counter.

- FI_WAIT_UNSPEC
Specifies that the user will only wait on the counter using fabric interface calls,
such as fi_cntr_wait. 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 event counter should use a wait set object to wait for events.
If specified, the wait_set field must reference an existing wait set object.

- FI_WAIT_FD
Indicates that the counter 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 counter should use a pthread mutex and cond variable as a wait
object.

- FI_WAIT_YIELD
Indicates that the counter will wait without a wait object but instead yield on
every wait. Allows usage of fi_cntr_wait through a spin.

wait_set
If wait_obj is FI_WAIT_SET, this field references a wait object to which the event
counter should attach. When an event is added to the event counter, 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 counters. This field is ignored if wait_obj is not FI_WAIT_SET.

flags Flags are reserved for future use, and must be set to 0.

fi_close
The fi_close call releases all resources associated with a counter. When closing the
counter, there must be no opened endpoints, transmit contexts, receive contexts or memory
regions associated with the counter. If resources are still associated with the counter
when attempting to close, the call will return -FI_EBUSY.

fi_cntr_control
The fi_cntr_control call is used to access provider or implementation specific details of
the counter. Access to the counter should be serialized across all calls when
fi_cntr_control is invoked, as it may redirect the implementation of counter operations.
The following control commands are usable with a counter:

FI_GETOPSFLAG (uint64_t *)
Returns the current default operational flags associated with the counter.

FI_SETOPSFLAG (uint64_t *)
Modifies the current default operational flags associated with the counter.

FI_GETWAIT (void **)
This command allows the user to retrieve the low-level wait object associated with
the counter. The format of the wait-object is specified during counter creation,
through the counter attributes. See fi_eq.3 for addition details using control
with FI_GETWAIT.

fi_cntr_read
The fi_cntr_read call returns the current value of the counter.

fi_cntr_readerr
The read error call returns the number of operations that completed in error and were
unable to update the counter.

fi_cntr_add
This adds the user-specified value to the counter.

fi_cntr_adderr
This adds the user-specified value to the error value of the counter.

fi_cntr_set
This sets the counter to the specified value.

fi_cntr_seterr
This sets the error value of the counter to the specified value.

fi_cntr_wait
This call may be used to wait until the counter reaches the specified threshold, or until
an error or timeout occurs. Upon successful return from this call, the counter will be
greater than or equal to the input threshold value.

If an operation associated with the counter encounters an error, it will increment the
error value associated with the counter. Any change in a counter’s error value will
unblock any thread inside fi_cntr_wait.

If the call returns due to timeout, -FI_ETIMEDOUT will be returned. The error value
associated with the counter remains unchanged.

It is invalid for applications to call this function if the counter has been configured
with a wait object of FI_WAIT_NONE or FI_WAIT_SET.

RETURN VALUES

       Returns  0  on  success.   On  error,  a  negative  value corresponding to fabric errno is
       returned.

       fi_cntr_read / fi_cntr_readerr
              Returns the current value of the counter.

       Fabric errno values are defined in rdma/fi_errno.h.

NOTES

       In order to support a variety of counter implementations, updates made to  counter  values
       (e.g. fi_cntr_set  or  fi_cntr_add)  may  not  be  immediately  visible  to  counter  read
       operations (i.e. fi_cntr_read or fi_cntr_readerr).  A  small,  but  undefined,  delay  may
       occur between the counter changing and the reported value being updated.  However, a final
       updated value will eventually be reflected in the read counter value.

       Additionally, applications should ensure that the value of a counter  is  stable  and  not
       subject  to  change  prior  to  calling  fi_cntr_set  or  fi_cntr_seterr.   Otherwise, the
       resulting value of the counter after fi_cntr_set / fi_cntr_seterr is undefined, as updates
       to  the counter may be lost.  A counter value is considered stable if all previous updates
       using fi_cntr_set / fi_cntr_seterr and results of related operations are reflected in  the
       observed value of the counter.

AUTHORS

       OpenFabrics.