1fi_cntr(3)                     Libfabric v1.14.0                    fi_cntr(3)
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NAME

6       fi_cntr - Completion and event counter operations
7
8       fi_cntr_open / fi_close
9              Allocate/free a counter
10
11       fi_cntr_read
12              Read the current value of a counter
13
14       fi_cntr_readerr
15              Reads the number of operations which have completed in error.
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17       fi_cntr_add
18              Increment a counter by a specified value
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20       fi_cntr_set
21              Set a counter to a specified value
22
23       fi_cntr_wait
24              Wait for a counter to be greater or equal to a threshold value
25

SYNOPSIS

27              #include <rdma/fi_domain.h>
28
29              int fi_cntr_open(struct fid_domain *domain, struct fi_cntr_attr *attr,
30                  struct fid_cntr **cntr, void *context);
31
32              int fi_close(struct fid *cntr);
33
34              uint64_t fi_cntr_read(struct fid_cntr *cntr);
35
36              uint64_t fi_cntr_readerr(struct fid_cntr *cntr);
37
38              int fi_cntr_add(struct fid_cntr *cntr, uint64_t value);
39
40              int fi_cntr_adderr(struct fid_cntr *cntr, uint64_t value);
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42              int fi_cntr_set(struct fid_cntr *cntr, uint64_t value);
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44              int fi_cntr_seterr(struct fid_cntr *cntr, uint64_t value);
45
46              int fi_cntr_wait(struct fid_cntr *cntr, uint64_t threshold,
47                  int timeout);
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ARGUMENTS

50       domain Fabric domain
51
52       cntr   Fabric counter
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54       attr   Counter attributes
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56       context
57              User specified context associated with the counter
58
59       value  Value to increment or set counter
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61       threshold
62              Value to compare counter against
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64       timeout
65              Time  in milliseconds to wait.  A negative value indicates infi‐
66              nite timeout.
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DESCRIPTION

69       Counters record the number of requested operations that have completed.
70       Counters  can  provide  a light-weight completion mechanism by allowing
71       the suppression of CQ completion entries.  They are useful for applica‐
72       tions  that only need to know the number of requests that have complet‐
73       ed, and not details about each request.  For example, counters  may  be
74       useful  for implementing credit based flow control or tracking the num‐
75       ber of remote processes that have responded to a request.
76
77       Counters typically only count successful completions.  However,  if  an
78       operation completes in error, it may increment an associated error val‐
79       ue.  That is, a counter actually stores two distinct values, with error
80       completions updating an error specific value.
81
82       Counters  are  updated following the completion event semantics defined
83       in fi_cq(3).  The timing of the update is based on the type of transfer
84       and any specified operation flags.
85
86   fi_cntr_open
87       fi_cntr_open allocates a new fabric counter.  The properties and behav‐
88       ior of the counter are defined by struct fi_cntr_attr.
89
90              struct fi_cntr_attr {
91                  enum fi_cntr_events  events;    /* type of events to count */
92                  enum fi_wait_obj     wait_obj;  /* requested wait object */
93                  struct fid_wait     *wait_set;  /* optional wait set */
94                  uint64_t             flags;     /* operation flags */
95              };
96
97       events A counter captures different types of events.  The specific type
98              which is to counted are one of the following:
99
100       - FI_CNTR_EVENTS_COMP
101              The  counter increments for every successful completion that oc‐
102              curs on an associated bound endpoint.  The type of completions –
103              sends  and/or receives – which are counted may be restricted us‐
104              ing control flags when binding the  counter  and  the  endpoint.
105              Counters  increment  on  all  successful completions, separately
106              from whether the operation generates an entry in an event queue.
107
108       wait_obj
109              Counters may be associated with a specific  wait  object.   Wait
110              objects  allow  applications  to  block until the wait object is
111              signaled, indicating that  a  counter  has  reached  a  specific
112              threshold.   Users may use fi_control to retrieve the underlying
113              wait object associated with a counter, in order  to  use  it  in
114              other system calls.  The following values may be used to specify
115              the type of wait object associated with a counter: FI_WAIT_NONE,
116              FI_WAIT_UNSPEC, FI_WAIT_SET, FI_WAIT_FD, FI_WAIT_MUTEX_COND, and
117              FI_WAIT_YIELD.  The default is FI_WAIT_NONE.
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119       - FI_WAIT_NONE
120              Used to indicate that the user will not block (wait) for  events
121              on the counter.
122
123       - FI_WAIT_UNSPEC
124              Specifies that the user will only wait on the counter using fab‐
125              ric interface calls, such as fi_cntr_wait.  In  this  case,  the
126              underlying  provider  may select the most appropriate or highest
127              performing wait object available, including custom  wait  mecha‐
128              nisms.   Applications that select FI_WAIT_UNSPEC are not guaran‐
129              teed to retrieve the underlying wait object.
130
131       - FI_WAIT_SET
132              Indicates that the event counter should use a wait set object to
133              wait  for  events.  If specified, the wait_set field must refer‐
134              ence an existing wait set object.
135
136       - FI_WAIT_FD
137              Indicates that the counter should use a file descriptor  as  its
138              wait mechanism.  A file descriptor wait object must be usable in
139              select, poll, and epoll routines.  However, a provider may  sig‐
140              nal  an  FD  wait object by marking it as readable, writable, or
141              with an error.
142
143       - FI_WAIT_MUTEX_COND
144              Specifies that the counter should use a pthread mutex  and  cond
145              variable as a wait object.
146
147       - FI_WAIT_YIELD
148              Indicates  that  the counter will wait without a wait object but
149              instead yield on  every  wait.   Allows  usage  of  fi_cntr_wait
150              through a spin.
151
152       wait_set
153              If  wait_obj is FI_WAIT_SET, this field references a wait object
154              to which the event counter should  attach.   When  an  event  is
155              added  to  the event counter, the corresponding wait set will be
156              signaled if all necessary conditions are  met.   The  use  of  a
157              wait_set  enables  an  optimized  method  of  waiting for events
158              across multiple  event  counters.   This  field  is  ignored  if
159              wait_obj is not FI_WAIT_SET.
160
161       flags  Flags are reserved for future use, and must be set to 0.
162
163   fi_close
164       The  fi_close  call  releases  all resources associated with a counter.
165       When closing the counter, there must be no opened  endpoints,  transmit
166       contexts,  receive  contexts  or  memory  regions  associated  with the
167       counter.  If resources are still associated with the counter  when  at‐
168       tempting to close, the call will return -FI_EBUSY.
169
170   fi_cntr_control
171       The  fi_cntr_control  call is used to access provider or implementation
172       specific details of the counter.  Access to the counter should be seri‐
173       alized  across all calls when fi_cntr_control is invoked, as it may re‐
174       direct the implementation of counter operations.  The following control
175       commands are usable with a counter:
176
177       FI_GETOPSFLAG (uint64_t *)
178              Returns  the  current  default operational flags associated with
179              the counter.
180
181       FI_SETOPSFLAG (uint64_t *)
182              Modifies the current default operational flags  associated  with
183              the counter.
184
185       FI_GETWAIT (void **)
186              This  command allows the user to retrieve the low-level wait ob‐
187              ject associated with the counter.  The format of the wait-object
188              is  specified  during  counter creation, through the counter at‐
189              tributes.  See fi_eq.3 for addition details using  control  with
190              FI_GETWAIT.
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192   fi_cntr_read
193       The fi_cntr_read call returns the current value of the counter.
194
195   fi_cntr_readerr
196       The  read error call returns the number of operations that completed in
197       error and were unable to update the counter.
198
199   fi_cntr_add
200       This adds the user-specified value to the counter.
201
202   fi_cntr_adderr
203       This adds the user-specified value to the error value of the counter.
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205   fi_cntr_set
206       This sets the counter to the specified value.
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208   fi_cntr_seterr
209       This sets the error value of the counter to the specified value.
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211   fi_cntr_wait
212       This call may be used to wait until the counter reaches  the  specified
213       threshold, or until an error or timeout occurs.  Upon successful return
214       from this call, the counter will be greater than or equal to the  input
215       threshold value.
216
217       If  an  operation  associated  with the counter encounters an error, it
218       will increment the error value associated with the counter.  Any change
219       in a counter’s error value will unblock any thread inside fi_cntr_wait.
220
221       If  the  call  returns  due to timeout, -FI_ETIMEDOUT will be returned.
222       The error value associated with the counter remains unchanged.
223
224       It is invalid for applications to call this function if the counter has
225       been configured with a wait object of FI_WAIT_NONE or FI_WAIT_SET.
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RETURN VALUES

228       Returns 0 on success.  On error, a negative value corresponding to fab‐
229       ric errno is returned.
230
231       fi_cntr_read / fi_cntr_readerr
232              Returns the current value of the counter.
233
234       Fabric errno values are defined in rdma/fi_errno.h.
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NOTES

237       In order to support a variety of counter implementations, updates  made
238       to  counter values (e.g. fi_cntr_set or fi_cntr_add) may not be immedi‐
239       ately visible to counter read operations (i.e. fi_cntr_read  or  fi_cn‐
240       tr_readerr).   A  small,  but  undefined,  delay  may occur between the
241       counter changing and the reported value being updated.  However, a  fi‐
242       nal updated value will eventually be reflected in the read counter val‐
243       ue.
244
245       Additionally, applications should ensure that the value of a counter is
246       stable and not subject to change prior to calling fi_cntr_set or fi_cn‐
247       tr_seterr.  Otherwise, the resulting value of the counter after  fi_cn‐
248       tr_set  / fi_cntr_seterr is undefined, as updates to the counter may be
249       lost.  A counter value is considered stable if all previous updates us‐
250       ing  fi_cntr_set / fi_cntr_seterr and results of related operations are
251       reflected in the observed value of the counter.
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SEE ALSO

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

257       OpenFabrics.
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261Libfabric Programmer’s Manual     2021-03-22                        fi_cntr(3)
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