Pivotal Greenplum 5.3
"gpconfig -s gp_enable_gpperfmon" always returns "off".
It seems to be specific to this one GUC although other GUCs may also be affected.
Use the command psql -c "show gp_enable_gpperfmon" to get the current setting.
This issue is being tracked with the issue number 29246. We will update once it is fixed.