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 */
void *vp; /* void 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