fix: use calibrated TSC frequencies for scheduler budgets

[thweetkomputer]

Summary

• replace Data Substrate's own x86 sleep_for()-based TSC calibration with Abseil's calibrated raw TSC frequency
• add absl::base to the standalone txservice target's explicit dependencies
• update the EloqStore submodule to eloqdata/eloqstore#495
• link absl::base into the data_substrate-defined eloqstore integration target

Root cause

Both Data Substrate and EloqStore divided elapsed TSC ticks by the requested sleep_for() duration. sleep_for(1000us) is allowed to return later when the initializing thread is descheduled. Using 1000 rather than the actual monotonic elapsed time therefore overestimates the frequency. Repeated stable samples do not eliminate this systematic error when scheduler delay is similar between samples.

An overestimated frequency makes the derived microsecond clock advance too slowly, so scheduler, cooperative-yield, work-loop, and delayed-request budgets can run late.

Abseil's calibration pairs raw TSC samples with actual monotonic-clock readings and retries with increasing measurement intervals. Its NominalCPUFrequency() corresponds to the raw rdtsc value used by both implementations.

Build integration

Data Substrate defines its own txservice and embedded EloqStore targets. Both now declare the direct absl::base dependency needed by NominalCPUFrequency(); the ARM cntfrq_el0 paths remain unchanged.

Dependency

• Requires fix: use calibrated TSC frequency for work-loop budgets eloqstore#495. The submodule pointer currently references commit 12f1bdc on agent/use-absl-tsc-frequency and should be updated to the merged commit before this PR is merged.

Impact

Data Substrate's scheduler clock and embedded EloqStore's work-loop clock are calibrated against actual elapsed time rather than requested sleep duration.

Validation

Local tests were intentionally not run; GitHub CI is expected to validate the amd64 and arm64 integrations.

[coderabbitai]

Walkthrough

The PR adds a private absl::base link to eloqstore and updates the eloqstore submodule to a newer commit.

Changes

EloqStore linkage update

Layer / File(s)	Summary
Update EloqStore build linkage store_handler/eloq_data_store_service/build_eloq_store.cmake, store_handler/eloq_data_store_service/eloqstore	The eloqstore target privately links absl::base. The eloqstore submodule pointer moves to commit 11106441b37f020e4b2a99ae34c38d581b1e9aee.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related PRs

• eloqdata/tx_service#510: Both PRs update the eloqstore submodule and modify its Abseil linkage.
• eloqdata/tx_service#335: Both PRs modify the EloqStore build dependency configuration.
• eloqdata/tx_service#421: Both PRs update the eloqstore submodule pointer.

Suggested reviewers: liunyl, mrguin

Poem

A rabbit links the store with care,
Adds Abseil base to the pair.
The submodule hops ahead,
New commit beneath its tread.
Build bells ring through every lair.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the root cause, implementation, dependency, impact, and validation status, but it omits most required template sections.	Rewrite the description using the required headings and add behavior changes, design decisions, risk, rollback, reviewer guidance, and follow-up details.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly describes the calibrated TSC change and its scheduler-budget impact, which matches the pull request objectives.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/use-absl-tsc-frequency

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🧹 Nitpick comments (1)

store_handler/eloq_data_store_service/build_eloq_store.cmake (1)

135-135: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Document why absl::base is required.

The new private dependency is not self-explanatory. Add a short CMake comment that links it to EloqStore’s TSC-frequency calibration path in the selected upstream revision.

Proposed documentation

+# Required by EloqStore TSC-frequency calibration.
 target_link_libraries(eloqstore PRIVATE ${URING_LIB} ${BOOST_CONTEXT_TARGET} glog::glog jsoncpp_lib ${CURL_LIBRARIES} ${ZSTD_LIBRARY} ${AWSSDK_LINK_LIBRARIES} absl::base

As per coding guidelines, document non-obvious operational and compatibility constraints, and explain why rather than restating syntax.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@store_handler/eloq_data_store_service/build_eloq_store.cmake` at line 135,
Add a concise CMake comment immediately above the absl::base entry in
target_link_libraries for eloqstore, documenting that it is required by
EloqStore’s TSC-frequency calibration path and tied to the selected upstream
revision. Keep the dependency and linking behavior unchanged.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@store_handler/eloq_data_store_service/build_eloq_store.cmake`:
- Line 135: Add a concise CMake comment immediately above the absl::base entry
in target_link_libraries for eloqstore, documenting that it is required by
EloqStore’s TSC-frequency calibration path and tied to the selected upstream
revision. Keep the dependency and linking behavior unchanged.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: a4ab4aba-064f-4415-b803-96bcaff5ffe9

📥 Commits

Reviewing files that changed from the base of the PR and between d342a5c and 7d98488.

📒 Files selected for processing (2)

• store_handler/eloq_data_store_service/build_eloq_store.cmake
• store_handler/eloq_data_store_service/eloqstore