Have noticed that the metrics.c file has been coded using the
perfstat_cpu_total system call, and was wondering about the reasoning in using
the perfstat_cpu_total CPU stats in preference to those produced via the
perfstat_partition_total system call ?
The reason I ask is that there seems to be a wide level of varience between the
CPU User and CPU Idle metrics produced by both system calls.
If someone understands the difference between the CPU metrics provided by these
two system calls, and why they would provide considerably different CPU User
and Idle metrics on a 2 CPU Aix 5.3 LPAR with no sharing of CPU's involved, I
would very interested to hear from you.
The standard Aix performance tools (vmstat, sar, topas, nmon) all seem to be
using the metrics provided by the perfstat_partition_total. This means (in my
case) that Ganglia's CPU User and CPU Idle graphs do no match what is shown to
be happening on that LPAR with the standard Aix Performance tools.
(ie. Ganglia graphs show LPARs with 30% ish idle time, but vmstat etc shows no
idle time).
Documentation on the perfstat_cpu_total system call seems to indicate that the
perfstat_partition_total system call should be used instead.
http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=/com.ibm.aix.basetechref/doc/basetrf1/perfstat_cputot.htm
Quote : All data consumers requiring processor use must be modified to support
PURR-based computations as shown in the example for the
perfstat_partition_total interface under Perfstat API programming.
While I'm confident that there is a good reason for the use of
perfstat_cpu_total in the aix/metrics.c source, I would like to understand the
reasoning and so banish any nervousness in trusting the stats provided the
Ganglia product.
Appreciate any information shedding light on this.
Thanks and Best Regards to all.
PS. My hat is off to the Ganglia Team/Community. :-) Very impressive product.
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