fi_cntr(3) Libfabric v1.15.1 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 imple- menting 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 oper- ation 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 ob- jects 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 fol- lowing values may be used to specify the type of wait object associ- ated 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 under- lying 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 vari- able as a wait object. - FI_WAIT_YIELD Indicates that the counter will wait without a wait object but in- stead 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 coun- ters. 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 re- sources 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 spe- cific 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 spec- ified 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 er- ror 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 re- flected 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. Libfabric Programmer's Manual 2021-03-22 fi_cntr(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | RETURN VALUES | NOTES | SEE ALSO | AUTHORS
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