Logstash Metricbeat field calculation

[PRASHANT_MEHTA]

I'm implementing ruby code through logstash pipeline,Unable to get desired fields created in kibana,what would be right approach to code in order to get desired result?
Want to get CPU % by adding two fileds and divide by no of cores.
ex:((a+b)/n)*100

Below code dosen't work:

ruby {
code => "
userpct = event.get('system.cpu.user.pct')
systempct = event.get('system.cpu.system.pct')
cores = event.get('system.cpu.cores')
cpuusage = (((userpct+systempct)/cores)*100)
if (cpuusage > 20)
event.set('system.cpuusage',cpuusage)
event.set('system.cpu.status','CPUCritical')
else
event.set('system.cpu.status','CPUHealthy')
end

				"
       }

---

Image:

[Badger]

@PRASHANT_MEHTA

system.cpu.user.pct

See this post. Try [system][cpu][user][pct]

[PRASHANT_MEHTA]

@Badger Thanx for your response! Tried the above way you mentioned,didn't worked.

---

filter
{
mutate { add_field => { "mount.point.usage" => "%{[host][name]} %{[system][filesystem][mount_point]}" } }

ruby {
         code => "
						  userpct = event.get([system][cpu][user][pct])
				          systempct = event.get([system][cpu][system][pct])
						  cores = event.get([system][cpu][cores])
					      cpuusage = (((userpct+systempct)/cores)*100)
                          if (cpuusage > 20)
						  event.set('system.cpuusage',cpuusage)
	                      event.set('system.cpu.status','CPUCritical')
						  else
						  event.set('system.cpu.status','CPUHealthy')
						  end
						  
				"
       }

}