Fork from T236675.
I have noticed a 20% increase in execution time running Docker container on a Stretch instance compared to a Jessie instance.
That disappear on Stretch when setting the kernel boot option `mitigations=off`
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* The benchmark is done running a python script (jenkins-job-builder) for integration/config
* The instances are on the same underlying machine (cloudvirt1028)
* There is barely any load on the server or on the instances at the time conducting the test
* Jessie has kernel 4.9.110-3+deb9u5~deb8u1
* Stretch has kernel 4.9.189-3+deb9u1
* I have ruled out nslcd vs sssd
* It is not related to the python version, they are the same in the container
* it is not glibc / libpthreads related or so. Based on comparison between `perf` reports
* it is not related to the Docker version
I have initially and intuitively thought about the Spectre meltdown and other CPU issues mitigations, but dismissed that early and went wasting time comparing other parameters.
Eventually, I have rebooted a machine with kernel boot option `mitigations=off` based on informations at https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/MDS
Result on three instances all on `cloudvirt1028`:
| Host | OS | Kernel option | Duration
| integration-agent-jessie-docker-1001 | **Jessie** | defaults | 55s (good)
| integration-agent-1008-docker | Stretch | defaults | 1m6s
| integration-agent-1005-docker | Stretch | defaults | 1m7s
| integration-agent-1005-docker | Stretch | **`mitigations=off`** | 55s (good)