This is an old revision of the document!
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