Only valid on P9 environment !! Remember to deactivate if lpar is pushed to a P8 server !!

A kernel scheduler tunable “vpm_fold_threshold” can be used to reduce physical CPU consumption by influencing the threshold at witch AIX unfolds or folds virtual cpu (VP) The default value is 49%. This helps P7 and P8 cpu architecture to privilege VP unfolding prior to use all threads in smt8 mode. As the P9 architecture is more optimized for multi-thread execution, it can handle larger vp fold thresholds with less single-thread performance impact.

Due to it's nature, the benefit of rising this tunable is mostly visible on lpars that have a large number of VP. This means: VP > 3

In dev environment and less real-time sensible production environments we therefore use a setting of 80% =⇒ vpm_fold_threshold = 80

In real-time sensible production, use a setting of 65-70**.

The schedo command is used to display or set the kernel scheduler tunables.

Command syntax:

[root@aix01]/root# schedo
Usage:  schedo -h [tunable] | {[-F] -L [tunable]} | {[-F] -x [tunable]}
        schedo [-p|-r] (-a [-F] | {-o tunable})
        schedo [-p|-r] [-y] (-D | ({-d tunable} {-o tunable=value}))

View:

[root@aix01]/root#  schedo -o vpm_fold_threshold
vpm_fold_threshold = 80

Set: (The new value is actif instantly)

[root@aix01]/root#  schedo -o vpm_fold_threshold=80
Setting vpm_fold_threshold to 80
Warning: a restricted tunable has been modified