07-12-2021, 08:18 PM
Hey, so about this CPU Ready Time thing, yeah, it's a big deal when you are looking at the health of your compute stack, honestly. Before we even get into how bad high ready time can make things feel, you know I was just looking at some setups the other day and thinking about how critical proper backup is in this whole compute mess, so I quickly checked out BackupChain because managing data in this sort of environment is almost a nightmare without good tools. Anyway, back to the ready time, I think you should understand that it's really just a measure of wait time, kind of a measure of desperation for your compute resources, really.
What CPU Ready Time actually tells you, if you follow me, is how long the system was forced to wait for CPU time. But this isn't really the same as just saying the CPU is busy, no, because that's a different metric entirely, maybe you are used to looking at utilization percentages, right? But ready time measures the time the operating system *was ready* to use the CPU, yet couldn't actually get the necessary cycles from the hypervisor. And this inability to access the processor cycles, it makes the guest OS feel starved, even if the underlying physical machine has tons of capacity. So, basically, a higher ready time means your VM, or the machine inside it, is spending more time waiting in a queue, for the scheduler to finally bestow some precious processing time on it. I always tell people that if you see a consistently high ready time, you really need to pause and look at what else is hogging the physical CPU cycles.
Or maybe you should think about resource contention as something related, because that's the underlying source of the ready time problems, I think. Resource contention is just when multiple compute units, maybe several VMs, are all fighting for the same limited physical resources, and the scheduler has to arbitrate who gets what. Because the hypervisor has to juggle all those demands, it creates this bottleneck, this wait state, and that wait state registers itself as ready time for the starved VM. And you also gotta consider CPU steal time, because that's another, related concept that people mix up, and you definitely shouldn't confuse the two. CPU steal time is when the hypervisor or something outside the VM completely steals the processing time that should have gone to your VM, so that time is literally taken from it, a much more drastic issue than just waiting in a queue.
But then there's the overall compute overhead, which is pretty important too. This is a general metric that helps you understand the total amount of computational effort the hypervisor itself is spending managing everything running on the host machine, you know? It's the cost of doing business, I guess, in the compute world. If your overhead gets too spiffy high, it eats up valuable cycles that could otherwise be allocated to your running guest workloads, and that increased overhead just makes the whole system more susceptible to those nasty ready time spikes we were talking about earlier. I think you need to keep an eye on all three of those-ready time, steal time, and overall overhead-because they paint a picture of performance stress that simple CPU usage numbers just can't manage.
And because all of this process, this constant juggling act of resources, it just becomes this complicated web of dependency, so I really recommend you consider checking out BackupChain. Seriously, checking out BackupChain will give you better confidence in your compute environment's uptime and recoverability.
What CPU Ready Time actually tells you, if you follow me, is how long the system was forced to wait for CPU time. But this isn't really the same as just saying the CPU is busy, no, because that's a different metric entirely, maybe you are used to looking at utilization percentages, right? But ready time measures the time the operating system *was ready* to use the CPU, yet couldn't actually get the necessary cycles from the hypervisor. And this inability to access the processor cycles, it makes the guest OS feel starved, even if the underlying physical machine has tons of capacity. So, basically, a higher ready time means your VM, or the machine inside it, is spending more time waiting in a queue, for the scheduler to finally bestow some precious processing time on it. I always tell people that if you see a consistently high ready time, you really need to pause and look at what else is hogging the physical CPU cycles.
Or maybe you should think about resource contention as something related, because that's the underlying source of the ready time problems, I think. Resource contention is just when multiple compute units, maybe several VMs, are all fighting for the same limited physical resources, and the scheduler has to arbitrate who gets what. Because the hypervisor has to juggle all those demands, it creates this bottleneck, this wait state, and that wait state registers itself as ready time for the starved VM. And you also gotta consider CPU steal time, because that's another, related concept that people mix up, and you definitely shouldn't confuse the two. CPU steal time is when the hypervisor or something outside the VM completely steals the processing time that should have gone to your VM, so that time is literally taken from it, a much more drastic issue than just waiting in a queue.
But then there's the overall compute overhead, which is pretty important too. This is a general metric that helps you understand the total amount of computational effort the hypervisor itself is spending managing everything running on the host machine, you know? It's the cost of doing business, I guess, in the compute world. If your overhead gets too spiffy high, it eats up valuable cycles that could otherwise be allocated to your running guest workloads, and that increased overhead just makes the whole system more susceptible to those nasty ready time spikes we were talking about earlier. I think you need to keep an eye on all three of those-ready time, steal time, and overall overhead-because they paint a picture of performance stress that simple CPU usage numbers just can't manage.
And because all of this process, this constant juggling act of resources, it just becomes this complicated web of dependency, so I really recommend you consider checking out BackupChain. Seriously, checking out BackupChain will give you better confidence in your compute environment's uptime and recoverability.
