B2MS used 750 CPU Credits in 20 minutes

Question

B2MS used 750 CPU Credits in 20 minutes

Martin Bene 0

I've had a problem with a B2MS Windows VM burnng through 750 CPU credits within 20 minutes leaving the system throttled during business hours before it started recovering / regaining credits in the afternoon.

My understanding of how CPU credits are used suggests that it should be impossible for a B2MS to use tht many credits within 20 minutes.

Any idea what's going on and how to prevent something like this in the future?

cpu credits

Martin Bene 0 Reputation points

2023-02-16T14:12:26.6533333+00:00

Update: Cross checked with the diagram "Credits consumed" - no peak in the 10:00 to 10:30 time window.

So, it looks like the credits weren't actually consumed; instead, the saved credits remaining were just removed and the balance was reset to 60 - the starting point for a new B2MS VM.

Question still remains: Why and how to avoid it in the future.
Martin Bene 0 Reputation points

2023-02-16T14:12:38.7333333+00:00
Final Update: the root cause was found in the activity log:

Health Event Updated

with this information in the json:

"properties": { "title": "Live Migration", "details": "This virtual machine was paused for 1.020000 seconds due to a memory-preserving Live Migration operation. No additional action is required from you at this time.", "currentHealthStatus": "Available", "previousHealthStatus": "Available", "type": "Downtime", "cause": "PlatformInitiated" },

So, Azure decided to live migrate the VM to another Host and that caused the CPU credits to reset. That just leaves me with the cautionary information that the CPU credits may get reset at any time.

1 answer

Your answer

Martin Bene 0 Reputation points

2023-02-16T14:12:26.6533333+00:00

Update: Cross checked with the diagram "Credits consumed" - no peak in the 10:00 to 10:30 time window.

So, it looks like the credits weren't actually consumed; instead, the saved credits remaining were just removed and the balance was reset to 60 - the starting point for a new B2MS VM.

Question still remains: Why and how to avoid it in the future.
Martin Bene 0 Reputation points

2023-02-16T14:12:38.7333333+00:00

Final Update: the root cause was found in the activity log:

Health Event Updated

with this information in the json:

"properties": { "title": "Live Migration", "details": "This virtual machine was paused for 1.020000 seconds due to a memory-preserving Live Migration operation. No additional action is required from you at this time.", "currentHealthStatus": "Available", "previousHealthStatus": "Available", "type": "Downtime", "cause": "PlatformInitiated" },

So, Azure decided to live migrate the VM to another Host and that caused the CPU credits to reset. That just leaves me with the cautionary information that the CPU credits may get reset at any time.

Answer 1

@Martin Bene

Thanks very much for sharing the details and the updated root cause of the CPU credits being depleted. I am sharing a few links to the documentation in case you or others have questions about this.

B-series burstable virtual machine sizes

"When a VM is redeployed and the VM moves to another node, the accumulated credit is lost. If the VM is stopped/started, but remains on the same node, the VM retains the accumulated credit."

Maintenance for virtual machines in Azure

"Live migration can also be used to move VMs when Azure Machine Learning algorithms predict an impending hardware failure or when you want to optimize VM allocations."

B-series VMs are ideal for workloads that do not need the full performance of the CPU continuously, like web servers, proof of concepts, small databases and development build environments."

Please evaluate whether the current VM Size can meet your business requirements or not. If you have important business to run, to avoid the impact of CPU credit on performance, please consider using other VM SKUs with Non B-Series.

Please don’t forget to "Accept the answer" wherever the information provided helps you, this can be beneficial to other community members.

Share via

B2MS used 750 CPU Credits in 20 minutes

1 answer

Your answer