QmcIndom(3) — Linux manual page

NAME | C++ SYNOPSIS | DESCRIPTION | CONSTRUCTORS | DYNAMIC INDOMS | PROFILES | SEE ALSO | DIAGNOSTICS | BUGS | COLOPHON

QMCINDOM(3)             Library Functions Manual             QMCINDOM(3)

NAME         top

       QmcIndom - container for a instance domain description

C++ SYNOPSIS         top

       #include <QmcIndom.h>

       CC ... -lqmc -lpcp

DESCRIPTION         top

       A QmcIndom object represents a PMAPI(3) instance domain.  This
       includes a description of all the instances in the instance
       domain.

       A QmcInstance is a structure used to describe each instance in
       the instance domain.  This includes:

          - internal identifier. If this is less than zero, the instance
          is treated as a NULL entry in the instance table.

          - external name

          - reference count, ie. the number of QmcMetric objects
          referring to this instance.

          - the likely position of the instance in the pmResult from a
          pmFetch(3).  This is also used to indicate the position of the
          next NULL instance in the instance table, if this entry is
          also NULL.

          - a flag indicating if the instance was in the last
          pmGetInDom(3).

       The QmcIndom object has a list of QmcInstance structures, and
       various flags and counters to support dynamic instance domains
       where instances may come and go with each fetch and efficient
       profile generation.

CONSTRUCTORS         top

       QmcIndom::QmcIndom(int type, QmcDesc &desc);
           Calls pmGetInDom(3) and pmGetInDomArchive(3) for host and
           archive contexts to obtain the entire instance list for the
           instance domain of type and identified in desc.

DYNAMIC INDOMS         top

       The support of dynamic instance domains for live contexts is
       complex since many metrics may be referencing any of the
       instances in the domain.  Therefore the instance list may be
       sparse as the position of instances in the list must be
       maintained.

       When the instance domain is updated, instances may be removed
       from the list if they are not in the new instance list (as
       returned by pmGetInDom(3)) and is not referenced by any metrics.
       Each instance in the new list is then compared with the old list
       to determine which instances are still active, and any new
       instances need to be added.  An instance is considered the same
       if both the internal and external identifiers are the same.  New
       instances are first inserted into positions of deleted instances
       before being appended to the list.

       This algorithm is expensive (potentially O(N^2)).

       bool changed() const;
           Returns true if the instance domain may have changed in the
           last fetch.

       void newFetch();
           Reset the flags that may have indicated that the instance
           domain had changed.  This is called by QmcContext::fetch.

       void hasChanged();
           Set the flags to indicate that the instance domain may have
           changed.  This is called by QmcMetric::extractValues.

       int update();
           Update the instance domain as described above. On subsequent
           calls, before the next fetch, this method will remove any
           instances that are no longer referenced without updating the
           instance list with a pmGetInDom(3) call.

       uint_t numInsts() const;
           Returns the number of instances that are not NULL.

       uint_t numActiveInsts() const;
           Returns the number of instances that are active according to
           the last QmcIndom::update call.

       uint_t listLen() const;
           Returns the length of the instance list, including NULL
           instances.

PROFILES         top

       The algorithm for determining the most compact profile uses the
       number of instances (_instances.length()), the number of
       referenced instances (_count), the number of active instances
       (_numActive) and the number of referenced active instances
       (_numActiveRef).

               if (all active instances are referenced
                   or there are no active instances)

                       request all instances implicitly

               else if (the number of referenced instances
                        is less than the number of active
                        instances that are not referenced)

                       delete all instances from profile
                       add all referenced instances

               else

                       add all instances to profile
                       delete all instances that are not referenced

       bool diffProfile() const;
           Returns true if the profile has potentially changed since the
           last call to QmcIndom::genProfile.

       int genProfile();
           Generates a new profile for the instance domain. a PMAPI(3)
           error code is returned if the profile failed.

SEE ALSO         top

       PMAPI(3), QMC(3), QmcContext(3), QmcDesc(3), QmcMetric(3),
       pmFetch(3), pmflush(3), pmGetInDom(3), pmGetInDomArchive(3) and
       pmprintf(3).

DIAGNOSTICS         top

       Error messages are generated using pmprintf(3) but are not
       flushed. It is the responsibility of the user to call pmflush(3)
       to output any messages.

       Additional diagnostics may be activated by adding the options pmc
       and/or indom to the global debugging specification, as described
       in pmSetDebug(3).

BUGS         top

       User's have no control over the algorithm used to generate the
       profile. In the case of proc metrics, an implicit profile could
       be generated if all process instances are required, even though
       this will result in no values being returned in the fetch.

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at 
       ⟨http://www.pcp.io/⟩.  If you have a bug report for this manual
       page, send it to pcp@groups.io.  This page was obtained from the
       project's upstream Git repository
       ⟨https://github.com/performancecopilot/pcp.git⟩ on 2020-12-18.
       (At that time, the date of the most recent commit that was found
       in the repository was 2020-12-18.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Performance Co-Pilot               SGI                       QMCINDOM(3)

Pages that refer to this page: QMC(3)QmcContext(3)