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Operating Systems AIX High CPU Usage , users affected Post 302887021 by rbatte1 on Wednesday 5th of February 2014 06:06:47 AM
Old 02-05-2014
So, this is a partitioned server. It has an allocation of 1.3 CPUs. I'm assuming therefore that there are other partitions defined, and perhaps a little spare CPU on the chassis as a whole. If the partition is capped, then it will use up to 1.3 CPUs and no more. If it is uncapped and there is spare CPU then it will burst through the limit and you will see the value for entitled CPU on sar or vmstat exceeding 100%.

If you take the cap off the partition and other servers are busy, they will be guaranteed to get their allocated CPU as a minimum, however as already pointed out by Zaxxon, you are not CPU bound (95% entitled capacity)

Consider partitions:-
  1. 1.3 CPU shared
  2. 3.0 CPU shared
  3. 2.0 CPU dedicated
  4. 1.7 CPU shared
Server has 8 CPUs. Two are dedicated, so out of the reckoning. If the shared CPU partitions are all uncapped, then if the other two are idle, the busy one could get 6 CPUs. If all are busy, then they will be limited as shown. If partition 4 is idle and 1 & 2 are busy then they will compete for the spare CPU (after both have reached their entitled CPU limit) and you can weight them to show a preference.

You may be better just upping your CPU allocation a little then re-activating the partition (not just a reboot) else your end user will get used to having the full spare CPU available and then complain when it's in use elsewhere on the chassis. Is there another partition you could squeeze down, but take the cap off because it is rarely busy?

We have our set as 0.1 CPU, production uncapped, test/dev capped.



I hope that this helps.

Robin
Liverpool/Blackburn
UK
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cpu_get_info(3) 					     Library Functions Manual						   cpu_get_info(3)

NAME
cpu_get_info, cpu_get_num, cpu_get_max - Query CPU information for the platform (libc library) SYNOPSIS
#include <cpuset.h> int cpu_get_info( ncpu_info_t *info ); int cpu_get_num( void ); int cpu_get_max( void ); PARAMETERS
Points to an ncpu_info_t buffer to receive the CPU information for the booted configuration. DESCRIPTION
The cpu_get_info() function returns the following information about the platform CPU configuration in the buffer pointed to by the info parameter: Revision number. Maximum number of CPUs supported by the machine architecture. CPU processor set that is physically plugged into the system and recognized by the system console. Set of online CPUs in the caller's partition; that is, the set of CPUs on which the caller can schedule work. Set of CPUs in the partition that have processes bound to them. Set of CPUs in the partition whose processor set is marked for exclusive use. The CPU sets specified in the ncpu_info_t structure must have been created by the caller prior to the call. If the caller specifies zero for a CPU set, the function silently ignores filling in data for that set. The information returned by the cpu_get_info() function is relative to the caller's partition. The cpu_get_num() function returns the actual number of CPUs available in the caller's partition. The cpu_get_max() function returns the maximum number of CPUs, including unpopulated CPU slots, that can be configured in the system. NOTES
A cpu_get_info() call is similar to a getsysinfo(GSI_CPU_INFO, ...) call. The principal difference is that the main ncpu_info_t struc- ture fields returned by cpu_get_info() are of type cpuset_t, whereas the same information returned by getsysinfo()is of type ulong_t. Fur- thermore, a getsysinfo(GSI_CPU_INFO, ...) call returns information only about the first n CPUs, where n is the number of bits in a ulong_t field, or (sizeof(ulong_t)*8). For cpu_get_info(), the ncpu_version field of the info argument must be set to NCPU_INFO_VERSION prior to the call. RESTRICTIONS
The information returned by these functions is a snapshot of the platform/partition configuration at the time the information is sampled. The data may be stale by the time the caller uses the information. RETURN VALUES
The cpu_get_info() function returns the following values: Success. Failure. In this case, errno is set to indicate the error. The cpu_get_num() and cpu_get_max() functions return values as stated in the DESCRIPTION. These functions always complete successfully. ERRORS
The cpu_get_info() function fails, it sets errno to one of the following values: The info argument or one of the cpuset_t elements, points to an invalid address. One or more of the cpuset_t elements of the info argument points to an invalid CPU set, possibly one that was not created by cpusetcreate(). The version number specified in the ncpu_version field of the info argument is not recognized by the system. SEE ALSO
Functions: cpusetops(3), numa_intro(3) cpu_get_info(3)
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