[release/8.0] Metrics Feature Switch

[tarekgh]

Fixes #89880

Backport of #91767 to release/8.0

/cc @tarekgh

Customer Impact

The introduction of a feature switch enables the option to disable the metrics feature, aiding in trimming and AOT scenarios. This modification addresses and resolves the performance regression observed in Xamarin app startup scenarios. For additional information, please refer to the following issue: #89880.

Testing

Successfully ran all regressions test and added a new test covering testing when the new switch is enabled.

Risk

We haven't made any alterations or adjustments to the code or logic when the new switch is left disabled. Therefore, any modifications will only become apparent when the switch is activated. The risk of this change adversely affecting any existing, functional functionality is exceedingly low.

IMPORTANT: If this backport is for a servicing release, please verify that:

• The PR target branch is release/X.0-staging, not release/X.0.

• If the change touches code that ships in a NuGet package, you have added the necessary package authoring and gotten it explicitly reviewed.

[tarekgh]

CC @noahfalk @eerhardt

[tarekgh]

@ericstj please have a look and approve it if you don't see any concerns with it. Thanks!

[ericstj]

This LGTM and I approve for RC2.

One ask is to double check that this will integrate well by staging the changes you want to make in the SDK and confirming the right default / feature enabled behavior. I know I've mixed up defaults or true/false values more than once myself.

[ericstj]

@artl93 this is ready for your approval as well.

[tarekgh]

One ask is to double check that this will integrate well by staging the changes you want to make in the SDK and confirming the right default / feature enabled behavior. I know I've mixed up defaults or true/false values more than once myself.

I am currently doing some more tests. Please hold merging till I finish. nothing alarming so far :-)

[tarekgh]

@ericstj I have done more manual testing building and running as AOT. I confirmed when the switch is not defined or it is defined with true value, I see the metrics functionality is enabled and work as expected. When defining the switch with false value, I am seeing the new behavior which disables metrics functionality. I think we are good to go. I haven't done the SDK changes yet which I'll do more testing when having it.

[artl93]

@ericstj I have done more manual testing building and running as AOT. I confirmed when the switch is not defined or it is defined with true value, I see the metrics functionality is enabled and work as expected. When defining the switch with false value, I am seeing the new behavior which disables metrics functionality. I think we are good to go. I haven't done the SDK changes yet which I'll do more testing when having it.

For my education, what do you mean by, "When having it"? Do you mean after merge and the SDK is produced?

[ericstj]

This change in dotnet/runtime will require corresponding change in the SDK targets to expose this new feature to the build. Those changes will look similar to these:
https://github.com/search?q=repo%3Adotnet%2Fsdk+EventSourceSupport+language%3AXML&type=code&l=XML

[artl93]

M2 approved. Thanks!