Ready Time for Dual CPU machines

[nonu]

Looking at it in esxtop this morning it looks like the ready time displayed in the default view is a sum of all CPUS - so a ready time of 10% for a 2x box is 5% for each CPU??

Just wondering how we should approach this - typically I've always felt that 5-6% ready was OK, sometimes even 10%, but more then that not OK.

So does that imply that 10-20% for 2 Cpu is OK, and 30%-40% is okay for a 4way? Wondering what everyone's thoughts are...

[Abaronov]

Correct

This looks like a bug. It actually happens both in VIC and when you use VIC API to get the counters.

Thanks,

Andrei

[nonu]

Can Anyone of the admin or someone from Vmware confirm what "Abaronov " Just posted.

[etieseler]

What process %RDY are you looking at?

For the idle collumn this is a summation of all the CPU's, so if you have a 4 way host and all CPU's are idle then this will say 400.00.

For each VM you can have up to 100.00 for each CPU, so a 2 vSMP VM can have up to 200.00 %RDY, 1 vCPU can have up to 100.00.

Im not an engineer at VMware, but a ready time of 10% on a 2 way Vm would indicate around 5% per CPU, I'm sure its not perfectly divided however.

Here is my math: if max %RDY for a 2 CPU VM = 200, then 10% of 200 is the equivilant of 5% of 100

-Ed

[nonu]

Ed what ever you said made lot of sense,but still when i see at the esxtop stat,I am still not able to get how is it calculation the Ready time,

I am attaching the esxtop stats here First seven rows indicated the stats for the following processes as listed in the order and rest of them are for my VM's

Idle

system

console

helper

drivers

vmotion

vmware-vmkauth

do let me know how the percentage is calculated..from %idle and %used or anyother stat which corresponds to the calculation of the %ready

[etieseler]

%RDY is the % of time that the VM is ready to execute a command but waiting to be scheduled CPU time. It is a stand alone metric not related to the other collumns. It can be up to 100% per CPU assigned to the VM

%USED is the % of physical CPU used by the resource.

By the looks of your stats most of your VM's are vSMP? I would consider changing them to 1 vCPU. Using 2 CPU's when not needed can hurt the other VM's and result in higher %RDY times. I would consider #22,26,28,30,32,and 34 being single CPU VM's. #24 looks busy enough to need 2 vCPU's

Using 2 vCPU's when not needed can raise %RDY because ESX must schedule all the CPU's for a VM at the same time. So if 1 CPU is ready to accept a command, but all the others are busy the VM must wait until another CPU is available before it can execute. While that idle CPU is waiting all other VM's must wait for it to finish as well. Your VM's will spend more time waiting for CPU time than they need to.

Additionally, having multiple CPU's for single threaded applications will not improve the performance of the application. If the application is multi-threaded, such as SQL Server or Oracle, etc. then having 2 or more CPU can help.

Again, if all your VM's are 2 CPU when they do not need to be that may be a reason why ID #24 has a higher %RDY than it should.

-Ed