Override IOQueueCount via env vars

[EgorBo]

This PR adds ability to change default value for Socket.IOQueueCount in Kestrel - this will allow us to easily experiment with the default value on various many-cores system (or with different affinity settings) before we propose a better default here.

E.g. Current RPS on a many-cores arm64 CPU affinitized to 16 cores: 1.2M RPS (Windows)
Same setup with ASPNETCORE_IOQUEUECOUNT=10: 1.8M RPS.

cc @sebastienros

[davidfowl]

This should use our configuration system, not direct environment variables

[EgorBo]

This should use our configuration system, not direct environment variables

Can you please point me to an example?

[BrennanConroy]

It's also configurable via UseSockets

[amcasey]

It's not perfectly analogous, but here's an example of consuming new env vars: #44194

[ghost]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
To make sure no conflicting changes have occurred, please rerun validation before merging. You can do this by leaving an /azp run comment here (requires commit rights), or by simply closing and reopening.

[EgorBo]

Thanks! will configure with code

[ghost]

Hi @EgorBo. It looks like you just commented on a closed PR. The team will most probably miss it. If you'd like to bring something important up to their attention, consider filing a new issue and add enough details to build context.