Understanding CPU on AIX Power SMT Systems
ardentperf.com
ardentperf.com
Changing the profile from say P8 to P9_base to P9 changes things under the hood in terms of processor capabilities. This roughly translates into VM hardware versions in VMware-speak.
There are cores and then there are virtual processors as well as the notion of processor folding. Here's a starting point: https://www.ibm.com/support/pages/aix-virtual-processor-fold...
Some P9 specific changes re folding: https://www.ibm.com/downloads/cas/39XWR7YM
Source: I have to deal with POWER systems day to day.
I'm really not sure if I understood that "processor folding" correctly -> would that translate in the case of Intel/AMD/Linux to something like a "dynamic hyperthreading" done under-the-hood by the OS?
In addition to the reduction of VPs, you can consider setting the schedo tunable “vpm_throughput_mode” to a value of 2. By default, running in raw throughput mode (i.e. vpm_throughput_mode=0) AIX spreads all available work across as many VPs as available, dispatching work first to the primary SMT thread of each VP, then the secondary SMT threads, and so on, thus providing the best performance in most workloads. This configuration, however, can lead to a higher PC (processor capacity) utilized by the LPAR. Depending the workload, you can reduce the PC by setting the vpm_throughput_mode tunable to 2, thus having AIX to schedule work to the primary and secondary threads equally.
It was already “dead” when I first worked on it more than a decade ago. I think it’s a lot easier to replace with Linux than mainframes too. Doesn’t have a really good moat.