How Virtual CPU & Logical CPU works?
Experts (wmp) -
I would like to understand the how the Virtual CPU works in AIX Lpar config?
What is the optimal value that we can specify in the following config?
SMT = 4
PHY CPU = 16
VCPU = 20 ?
Logical CPU = ?
When we plot the % CPU report using NMON the logical CPU never match with the Physical CPU %. How do we fix this issue?
Thanks,
sve
I would like to understand the how the Virtual CPU works in AIX Lpar config?
What is the optimal value that we can specify in the following config?
SMT = 4
PHY CPU = 16
VCPU = 20 ?
Logical CPU = ?
When we plot the % CPU report using NMON the logical CPU never match with the Physical CPU %. How do we fix this issue?
Thanks,
sve
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OK.
Please be aware that under "LPAR" youre seeing real values from the server perspective, whereas "CPU_ALL" shows what the LPAR itself assumes to be real.
"CPU_ALL" shows what the LPAR did with the CPU cycles allocated to it by the hypervisor - thus the values User+Sys+Wait+Idle add up to ~100% which says nothing about the consumption of real hardware resources.
"CPU_ALL" does not show Physical CPU %!
And forget this "Logical CPU" value!
It's just ( Virtual CPUs * SMT factor ) and has nothing to do with resource consumption.
wmp
Please be aware that under "LPAR" youre seeing real values from the server perspective, whereas "CPU_ALL" shows what the LPAR itself assumes to be real.
"CPU_ALL" shows what the LPAR did with the CPU cycles allocated to it by the hypervisor - thus the values User+Sys+Wait+Idle add up to ~100% which says nothing about the consumption of real hardware resources.
"CPU_ALL" does not show Physical CPU %!
And forget this "Logical CPU" value!
It's just ( Virtual CPUs * SMT factor ) and has nothing to do with resource consumption.
wmp
ASKER
Great and Thanks for the nice help.
Oracle OEM and other monitoring tools does not reflect the Physical CPU %. It always match with the logical CPU. some of our CPU % based reporting based on OEM and these tools which are not accurate.
We've also created a SR with oracle to see whats going on at their end.
Thanks again.
sve.
Oracle OEM and other monitoring tools does not reflect the Physical CPU %. It always match with the logical CPU. some of our CPU % based reporting based on OEM and these tools which are not accurate.
We've also created a SR with oracle to see whats going on at their end.
Thanks again.
sve.
Ok, but please don't stress that term "Logical CPU" too much.
What you mean is "Virtual CPU" as opposed to "Physical CPU".
To repeat it: Logical CPU is Virtual CPU times SMT factor!
What you mean is "Virtual CPU" as opposed to "Physical CPU".
To repeat it: Logical CPU is Virtual CPU times SMT factor!
ASKER
Thanks for the help.
ASKER
That an AWESOME explanation that I ever could get. I was also going thru all your previous post related to NMON and LPAR to learn more about this.
We've been keeping the NMON and TOPas snapsnots for last 12 months. When we generate the NMON analyzer report out of it, it will create a pretty neat excel output (like the one attached).
I've a question from the output(excel)
The TAB LPAR shows Physical CPU vs. Entitlement and LCPU %.
Another TAB ALL_CPU shows Physical CPU %.
Why this Physical CPU % <> Logical CPU % in LPAR tab while the entitlement says all the physical cpus are fully engaged as you see in the LPAR tab?
Thanks for you valuable time.
Sve.
Book15.xlsx