pmsetmode(3) — Linux manual page

NAME | C SYNOPSIS | DESCRIPTION | EXAMPLES | LARGE DELTA VALUES | SEE ALSO | DIAGNOSTICS | COLOPHON

PMSETMODE(3)            Library Functions Manual            PMSETMODE(3)

NAME         top

       pmSetMode - set collection time parameters for the current PMAPI
       context

C SYNOPSIS         top

       #include <pcp/pmapi.h>

       int pmSetMode(int mode, const struct timeval *when, int delta);

       cc ... -lpcp

DESCRIPTION         top

       pmSetMode is used to define the collection time and/or mode for
       accessing performance metrics and meta-data in the current
       Performance Metrics Application Programming Interface (PMAPI)
       context.  This mode affects the semantics of subsequent calls to
       the following PMAPI routines: pmFetch(3), pmFetchArchive(3),
       pmLookupDesc(3), pmGetInDom(3), pmLookupInDom(3) and
       pmNameInDom(3).

       If mode is PM_MODE_LIVE then all information is returned from the
       active pool of performance metrics as of the time that the PMAPI
       call is made, and the other two parameters to pmSetMode are
       ignored.  PM_MODE_LIVE is the default mode when a new PMAPI
       context of type PM_CONTEXT_HOST is created.

       If the mode is not PM_MODE_LIVE, then the when parameter defines
       a time origin, and all requests for meta-data (metric
       descriptions and instance identifiers from the instance domains)
       will be processed to reflect the state of the meta-data as of the
       time origin, i.e. we use the last state of this information at,
       or before, the time origin.

       If the mode is PM_MODE_INTERP then, in the case of pmFetch(3),
       the underlying code will use an interpolation scheme to compute
       the values of the metrics from the values recorded for times in
       the proximity of the time origin.  A mode of PM_MODE_INTERP may
       only be used with an archive context.

       If the mode is PM_MODE_FORW then, in the case of pmFetch(3), the
       collection of recorded metric values will be scanned in a
       forwards direction in time, until values for at least one of the
       requested metrics is located after the time origin, and then all
       requested metrics stored in the set of archives at that time will
       be returned with the corresponding timestamp.  A mode of
       PM_MODE_FORW may only be used with an archive context.

       If the mode is PM_MODE_BACK then, the situation is the same as
       for PM_MODE_FORW, except a pmFetch(3) will be serviced by
       scanning the collection of recorded metrics in a backwards
       direction in time for metrics before the time origin.  A mode of
       PM_MODE_BACK may only be used with an archive context.

       If the mode is PM_MODE_FORW or PM_MODE_BACK, and no qualifying
       metrics can be found in the requested direction of searching
       before the end or start of the set of archive logs is found, then
       pmFetch(3) returns the special error indicator, PM_ERR_EOL.

       For modes other than PM_MODE_LIVE, after each successful
       pmFetch(3), the time origin is reset to the timestamp returned
       via the pmResult structure from pmFetch(3).

       The pmSetMode parameter delta defines an additional number of
       time units that should be used to adjust the time origin
       (forwards or backwards), after the new time origin from the
       pmResult has been determined.  This automatic adjustment of the
       time origin only occurs when the mode is PM_MODE_INTERP, and the
       adjustment is applied, even if the pmFetch(3) fails because the
       time origin is outside the range defined by the records in a set
       of archive logs, i.e. returns PM_ERR_EOL.

       By default delta is interpreted as milliseconds (but see the
       LARGE DELTA VALUES section below).

       Using these mode options, an application can implement replay,
       playback, fast forward, reverse, etc. for performance metric
       values held in the set of archive logs by alternating calls to
       pmSetMode and pmFetch(3).

       As a special case, if when is NULL then the mode and delta
       arguments are used as described above, but the current time in
       the archive is not altered.

EXAMPLES         top

       The following code fragment may be used to dump just those values
       recorded in an archive in correct temporal sequence, for a
       selected set of performance metrics; this uses the default
       collection time mechanisms.

            pmNewContext(PM_CONTEXT_ARCHIVE, "myarchive");
            while (pmFetch(npmid, pmidlist, &result) != PM_ERR_EOL) {
                /*
                 * process real metric values as of result->timestamp
                 */
                . . .
                pmFreeResult(result);
            }

       Alternatively, to replay interpolated metrics from the log in
       reverse chronological order, at 10 second intervals (of recorded
       time), the following code fragment could be used.

            struct timeval mytime;

            mytime.tv_sec = 0x7fffffff; /* or use pmGetArchiveEnd(&mtime) */
            pmSetMode(PM_MODE_BACK, &mytime, 0);
            pmFetchArchive(&result);
            mytime = result->timestamp;
            pmFreeResult(result);
            pmSetMode(PM_MODE_INTERP | PM_XTB_SET(PM_TIME_SEC), &mytime, -10);

            while (pmFetch(numpmid, pmidlist, &result) != PM_ERR_EOL) {
                /*
                 * process interpolated metric values as of
                 * result->timestamp
                 */
                . . .
                pmFreeResult(result);
            }

LARGE DELTA VALUES         top

       Because delta is an int and treated as milliseconds by default
       there is a limit on the maximum absolute value of delta that can
       be specified with this default interpretation, namely about 24
       days if a signed int has 31 bits of precision.  To accommodate
       longer values of delta the high-order bits of the mode parameter
       is also used to optionally set the units of time for the delta
       parameter. To specify the units of time use the PM_XTB_SET macro
       with one of the values PM_TIME_NSEC, PM_TIME_MSEC, PM_TIME_SEC,
       etc.  to set the mode as follows:

            PM_MODE_INTERP | PM_XTB_SET(PM_TIME_XXXX)

       The following code shows how this could be done if the desired
       delta is initially encoded in interval (a struct timeval).

            struct timeval interval;
            int mode;

            mode = ...

            if (abs(interval.tv_sec / (3600*24)) <= 24) {
                /* default encoding of milliseconds is fine */
                mode = PM_MODE_INTERP;
                delta = interval.tv_sec * 1000 + (interval.tv_usec + 500)/ 1000;
            }
            else {
                /* encode delta in units of seconds */
                mode = PM_MODE_INTERP | PM_XTB_SET(PM_TIME_SEC);
                delta = interval.tv_sec + (interval.tv_usec + 500000)/ 1000000;
            }

       For millisecond encoding of delta, using PM_XTB_SET(PM_TIME_MSEC)
       is functionally equivalent to not using PM_XTB_SET at all.

SEE ALSO         top

       PMAPI(3), pmFetch(3), pmFetchArchive(3), pmGetInDom(3),
       pmLookupDesc(3), pmLookupInDom(3) and pmNameInDom(3).

DIAGNOSTICS         top

       PM_ERR_MODE
              The mode parameter is invalid

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               PCP                      PMSETMODE(3)

Pages that refer to this page: pcpintro(1)pcpintro(3)pmapi(3)pmfetch(3)pmfetcharchive(3)pmfetchgroup(3)pmgetarchiveend(3)pmnewcontext(3)pmstore(3)pmtime(3)QmcGroup(3)