/cc Eric and Julz: Could you maybe help us understand this? Thanks!

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From: cf-dev@... <cf-dev@...> on behalf of Grifalconi, Michael <michael.grifalconi@...>
Sent: Monday, March 26, 2018 10:54:32 AM
To: cf-dev@...
Subject: [CAUTION] [cf-dev] Understanding hard CPU limits

 

Hi,

We were trying out the hard CPU limit as per docs
https://github.com/cloudfoundry/garden-runc-release/releases?after=v1.9.2

Releases · cloudfoundry/garden-runc-release · GitHub github.com GitHub is where people build software. More than 27 million people use GitHub to discover, fork, and contribute to over 80 million projects.

according to formula for single core machine,

APP_MEM_IN_MB * 100us / 1000 = MILLISECONDS_PER_100_MILLISECOND_PERIOD

In our tests, to get 6.4% CPU usage on a 64MB application and ~100% for a 1GB application we had to set the 'cpu_quota_per_share_in_us' to 3200. (Cell has 4 core and 16GB or ram, overcommit factor of 2).

That changes the formula to:
APP_MEM_IN_MB * 100us / 32000 = MILLISECONDS_PER_100_MILLISECOND_PERIOD

Can you help us to understand from where this 'times 32' comes from? Is the total available RAM of the cell (16GB * overcommit of 2) and number of cpu cores does not matter?

Thanks and regards,
Michael