TL;DR: Would reduce CI pressure by cancelling more "unnecessary" runs
but I can't verify without running a merge queue.
A common development pattern is to push a change and then immediately
check CI results. Follow-up fix pushes are quite common, which leads to
multiple CI runs being queued for the same pull request.
In Cloud Hypervisor, the size and cost of the CI matrix means that
several consecutive pushes (for example 3-4 in a short time) put
significant pressure on CI runners and noticeably increase feedback
latency.
In practice, concurrency handling is especially tricky for the merge
queue. From personal experience: If one does not take special care, CI
runs triggered by a `merge_group` can cancel each other, as in a merge
queue there are two runs for each job by default: one for the normal PR
and one for the merge commit. This is easy to run into, also because the
available documentation and best practices for this feature are not very
good.
At the same time, our workflows do not run on `push` events, but only
on `pull_request` and `merge_group`. Because of this, using
`${{ github.ref }}` alone as a concurrency key is not very meaningful,
and in practice only few runs are actually cancelled for successive PR
updates. Therefore, we should improve the usage of this feature.
This change tries to improve the situation by refining the concurrency
group key. The goal is to keep cancellation for multiple PR pushes,
while at the same time preventing unintended cancellations in the merge
queue by separating `merge_group` runs from regular PR runs.
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
And clean up some of the whitespace formatting so that the "name" and
"on" are grouped away from the "jobs".
Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
