fi_cntr(3)

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, deprecated */
        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.

- FI_CNTR_EVENTS_BYTES
    The counter is incremented by the number of user bytes, excluding any CQ data, transferred in a transport message upon reaching the specified completion semantic. For initiator side counters, the count reflects the size of the requested transfer and is updated after the message reaches the desired completion level (FI_INJECT_COMPLETE, FI_TRANSMIT_COMPLETE, etc.). For send and write operations, the count reflects the number of bytes transferred to the peer. For read operations, the count reflects the number of bytes returned in a read response. Operations which may both write and read data, such as atomics, behave as read operations at the initiator, but writes at the target. For target side counters, the count reflects the size of received user data and is incremented subject to target side completion semantics. In most cases, this indicates FI_DELIVERY_COMPLETE, but may differ when accessing device memory (HMEM). On error, the tranfer size is not applied to the error field, that field is increment by 1. The FI_COLLECTIVE transfer type is not supported.

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 (deprecated), 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 (deprecated)
    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 (deprecated)
    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 (deprecated)
    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.

Applications must manage counter values that approach the limit defined by the domain attribute max_cntr_value. This value, which defaults to UINT64_MAX but may be lower due to provider limitations, defines the maximum value returned by fi_cntr_read().

When a counter reaches its maximum value and additional operations complete, the counter behavior will be undefined. Applications that need to track the total number of operations beyond the provider’s counter limits are responsible for detecting and handling this condition by resetting counters with fi_cntr_set before they reach the maximum, or it could result in incorrect values.

  fi_cntr_readerr

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

Applications must manage error counter values that approach the limit defined by the domain attribute max_err_cntr_value. This value, which defaults to UINT64_MAX but may be lower due to provider limitations, defines the maximum value returned by fi_cntr_readerr().

When an error counter reaches its maximum value and additional error operations complete, the counter behavior will be undefined. Applications that need to track the total number of error operations beyond the provider’s counter limits are responsible for detecting and handling this condition by resetting the error counters with fi_cntr_set before they reach the maximum, or it could result in incorrect values.

  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.

SEE ALSO

fi_getinfo(3), fi_endpoint(3), fi_domain(3), fi_eq(3), fi_poll(3)

AUTHORS
OpenFabrics.