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pmconvscale(3)


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 pmLookupDesc(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
   input 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
   performance metric.

   pmConvScale is most useful when values returned  via  pmFetch(3),  (and
   possibly  extracted using pmExtractValue(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.

SEE ALSO

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

DIAGNOSTICS

   PM_ERR_CONV

          iunit   and   ounit   have  different  dimensionality,  or  have
          inappropriate type

   PM_ERR_UNIT

          Inappropriate iunit or ounit parameter



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