[Bugfix] [SpecDecode] AsyncMetricsCollector: update time since last collection

[tdoublep]

Fix #6577

IDK if I misunderstood something here, but looks like we basically sync the metrics every time (unless one is in-flight) and don't respect the collect_interval_s after the very first collection.

cc @cadedaniel @njhill

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.
Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which consists a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of default ones by unblocking the steps in your fast-check build on Buildkite UI.

Once the PR is approved and ready to go, please make sure to run full CI as it is required to merge (or just use auto-merge).

To run full CI, you can do one of these:

• Comment /ready on the PR
• Add ready label to the PR
• Enable auto-merge.

🚀

[tdoublep]

I added a test to catch this, it fails on main.

Pretty confident that this is in fact a bug now.

It effectively defeats the whole purpose of trying to copy the tensors periodically 😄

Fixing this can potentially improve performance.

/ready

[cadedaniel]

Great catch, thanks for adding a test as well :)

[cadedaniel]

Can we get a force merge for the intel test? @simon-mo ty

[simon-mo]

🫡