Stabilize performance test SLAs with tolerance thresholds

[aviralgarg05]

Fixes #14793

Context

This change adds tolerance thresholds to SLA checks that previously used strict equality for request counts/rates. Due to timing variations in test execution, actual counts can vary slightly from expected values, causing false SLA failures.

As noted in the PR #14429 discussion, the SLA failures in performance tests were identified as a separate issue to address. The pattern for handling this already exists in load-test/main.go which uses a 0.1% threshold.

Proposed Changes

• scale-from-zero SLA 3: Changed from strict equality (results.Requests == uint64(parallel)) to allow 1 request tolerance. This handles cases like "24 requests when 25 expected" due to timing.

• dataplane-probe SLA 2: Changed from strict equality to 0.1% tolerance (minimum 1 request), matching the pattern in load-test.

• rollout-probe SLA 2: Changed from math.Round(results.Rate) == rate.Rate(time.Second) to allow 1% rate tolerance using math.Abs(results.Rate-expectedRate) <= tolerance.

Files Changed

File	Change
test/performance/benchmarks/scale-from-zero/main.go	SLA 3: 1 request tolerance
test/performance/benchmarks/dataplane-probe/main.go	SLA 2: 0.1% tolerance
test/performance/benchmarks/rollout-probe/main.go	SLA 2: 1% rate tolerance

Verification

• go build ./test/performance/... - Passed
• go vet ./test/performance/benchmarks/... - Passed
• gofmt -s -d - No formatting issues
• DCO sign-off included in commit

Release Note

Performance test SLAs now use tolerance thresholds instead of strict equality checks for request counts/rates, reducing false failures due to timing variations.

[knative-prow]

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[knative-prow]

Hi @aviralgarg05. Thanks for your PR.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.21%. Comparing base (2cd582b) to head (737e48a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16371      +/-   ##
==========================================
+ Coverage   80.18%   80.21%   +0.02%     
==========================================
  Files         216      216              
  Lines       13440    13440              
==========================================
+ Hits        10777    10781       +4     
+ Misses       2298     2296       -2     
+ Partials      365      363       -2     

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