GetTotalPauseDuration implementation (#68835)

[cshung]

Backport of #68835 to release/6.0-staging

Customer Impact

One of our first-party customers reported that they need GC.GetTotalPauseDuration to help with their autoscaling. Here is what he said:

We need GC.GetTotalPauseDuration in order to accurately measure the impact of GC in our services and in order for us to have actionable signals to manage autoscaling policies. We have faced numerous customer-impacting Sev2 incidents where a .NET process was CPU-limited yet not consuming 100% CPU, which in several distinct cases we concluded was due to Workstation GC pauses. With GC.GetTotalPauseDuration, we will be able to accurately measure how close we are to hitting CPU limits, which enables us to configure appropriate autoscaling policies that would help us avoid customer impact. While the existing EventCounter “time-in-gc” helps to some extent, it is a noisy and unreliable source because it doesn’t measure the actual average time in GC, just the average time in GC for the most recent GC, which is skewed since not all GC’s are comparable (different gen’s, compacting Vs. not, etc.)

Testing

• GC Perf Sim
  • Normal Server
  • Normal Workstation
  • Large Pages Server
  • Large Pages Workstation
  • Low Memory Container
  • High Memory Load
• Microbenchmarks
  • V8 Test
  • Top 20 Microbenchmarks
• ASPNet Benchmarks
  • JsonMin - Windows

Risk

Low, this is an additional API. Any existing code that does not call the new API should not be affected at all.

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Tagging subscribers to this area: @dotnet/gc
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Issue Details

---

null

Author:	cshung
Assignees:	cshung
Labels:	area-GC-coreclr, new-api-needs-documentation
Milestone:	-

[carlossanlop]

@cshung I see this is still a draft. Today is code complete for the July release. If you want this change to be included in that release, please get a tactics approval, a sign-off, confirm the CI failures are unrelated, and merge it before EOD today.

[carlossanlop]

@cshung I see this is still a draft. Reminder - Tomorrow Monday 10th is Code Complete for the August Release. If you intend to get this fix included in that servicing release, please make sure to get a Tactics approval and merge the PR before 4pm, because that's when I close the branches to start merging staging into internal.

[jeffschwMSFT]

approved. please get a code review. we will take for consideration in 6.0.x

[jeffschwMSFT]

no-merge can be removed once review feedback addressed

[Maoni0]

LGTM!