NAME

       pmConvScale - rescale a performance metric value

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmConvScale(int type, const pmAtomValue *ival, const pmUnits *iunit, pmAtomValue *oval,
               const pmUnits *ounit);

       cc ... -lpcp

DESCRIPTION

       All performance metric values may be encoded in a pmAtomValue union, defined as follows;

            typedef union {
                __int32_t    l;     /* 32-bit signed */
                __uint32_t   ul;    /* 32-bit unsigned */
                __int64_t    ll;    /* 64-bit signed */
                __uint64_t   ull;   /* 64-bit unsigned */
                float        f;     /* 32-bit floating point */
                double       d;     /* 64-bit floating point */
                char         *cp;   /* char ptr */
                pmValueBlock *vbp;  /* pmValueBlock ptr */
            } pmAtomValue;

       The encoding of a performance metric's dimensionality and scale uses a pmUnits structure; see pmLookupDe‐
       sc(3).

       Given a performance metric value pointed to by ival multiply it by a scale factor and return the value in
       oval.  The scaling takes place from the units defined by iunit into the units defined by ounit.  Both in‐
       put and output units must have the same dimensionality.

       The  performance  metric type for both input and output values is determined by type, the value for which
       is typically extracted from a pmDesc structure, following a call to pmLookupDesc(3) for a particular per‐
       formance metric.

       pmConvScale is most useful when values returned via pmFetch(3), (and possibly extracted using  pmExtract‐
       Value(3)) need to be normalized into some canonical scale and units for the purposes of computation.

       As a special case, if all components of the dimension are zero, then this is treated as synonymous with a
       ``count''  dimension  of one, and so the ``count'' scale components determine the relative scaling.  This
       accommodates the case where performance metrics are dimensionless, without special case handling  on  the
       part of the caller.

DIAGNOSTICS

       PM_ERR_CONV

              iunit and ounit have different dimensionality, or have inappropriate type

       PM_ERR_UNIT

              Inappropriate iunit or ounit parameter

SEE ALSO

       PMAPI(3), pmAtomStr(3), pmExtractValue(3), pmFetch(3), pmLookupDesc(3), pmPrintValue(3), pmTypeStr(3) and
       pmUnitsStr(3).

Performance Co-Pilot                                   PCP                                        PMCONVSCALE(3)