Add per-thread CPU stats reporting in JSON output#346
Add per-thread CPU stats reporting in JSON output#346fcostaoliveira wants to merge 5 commits intomasterfrom
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Report per-second, per-thread CPU usage in JSON output using native OS APIs (Mach thread_info on macOS, pthread_getcpuclockid on Linux). Fix unsigned underflow when sampling finished threads. Add psutil-based external validation test and enforce no thread reports 100% CPU. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Use gettimeofday to measure real elapsed time between samples instead of assuming exactly 1 second. The sleep(1) plus loop processing meant the actual interval always exceeded 1s, systematically inflating CPU percentages and potentially exceeding 100%. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
| env.assertTrue('Thread 0' in second_data) | ||
| thread_cpu = second_data['Thread 0'] | ||
| env.assertTrue(thread_cpu >= 0) | ||
| env.assertTrue(thread_cpu < 100) |
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CPU percentage rounding can break strict less-than-100 assertions
Medium Severity
The C++ code writes CPU percentages to JSON using "%.2f" formatting, which rounds values like 99.995% up to 100.00. The tests assert thread_cpu < 100, which fails when parsing 100.00 from JSON. The high-load test (500 clients, 1 thread, pipeline 100) is specifically designed to drive CPU near 100%, making this rounding-induced failure realistic on fast multi-core systems. Additionally, the wall time is measured with gettimeofday (non-monotonic), so an NTP clock adjustment could produce cpu_pct > 100% directly.
Additional Locations (2)
Compare total process CPU (all threads) from both sources instead of trying to isolate worker threads. psutil sees internal threads (libevent, I/O) that memtier doesn't report in JSON, which inflated the external "worker" sum and caused the cross-validation to fail. Also widen tolerance to 25pp to account for untracked internal threads. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
| addTLSArgs(benchmark_specs, env) | ||
| config = get_default_memtier_config(threads=2, clients=5, requests=1000) | ||
| master_nodes_list = env.getMasterNodesList() | ||
| overall_expected_request_count = get_expected_request_count(config) |
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Unused variable in CPU stats test
Low Severity
The variable overall_expected_request_count is computed using get_expected_request_count(config) but never used anywhere in the test_cpu_stats_in_json function. This is dead code that should be removed to keep the test clean and maintainable.
| gettimeofday(&cpu_cur_tv, NULL); | ||
| double wall_usec = (double)(cpu_cur_tv.tv_sec - cpu_prev_tv.tv_sec) * 1000000.0 | ||
| + (double)(cpu_cur_tv.tv_usec - cpu_prev_tv.tv_usec); | ||
| if (wall_usec < 1.0) wall_usec = 1.0; // guard against division by zero |
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Wall clock adjustment causes incorrect CPU percentages
Low Severity
If the system clock is adjusted backwards (via NTP, daylight saving, or manual change) during benchmark execution, wall_usec becomes negative. The guard if (wall_usec < 1.0) wall_usec = 1.0 clamps it to 1 microsecond instead of handling the error condition properly, causing CPU deltas divided by 1.0 to produce wildly inflated percentages (potentially millions of percent) in the JSON output.
| unsigned long long main_prev_cpu = get_thread_cpu_usec(pthread_self()); | ||
| std::vector<unsigned long long> thread_prev_cpu(threads.size()); | ||
| for (size_t t = 0; t < threads.size(); t++) { | ||
| thread_prev_cpu[t] = get_thread_cpu_usec(threads[t]->m_thread); |
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Uninitialized pthread handle used for CPU measurement
High Severity
The code reads threads[t]->m_thread immediately after calling start() without verifying that thread creation succeeded. If pthread_create fails, m_thread remains uninitialized and passing it to get_thread_cpu_usec causes undefined behavior (potential crash when calling pthread_mach_thread_np on macOS or pthread_getcpuclockid on Linux with garbage pthread_t values).
Additional Locations (1)
Only call debugPrintMemtierOnError when the benchmark actually fails, preventing FileNotFoundError from missing Redis log files on success. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
| table.add_column(column); | ||
| } | ||
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| void run_stats::set_cpu_stats(std::vector<per_second_cpu_stats> cpu_stats) |
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CPU stats missing from aggregated results
Low Severity
When run_count > 1, average.aggregate_average(all_stats) computes aggregated output, but aggregate_average() never propagates/merges m_cpu_stats, so “AGGREGATED AVERAGE RESULTS” JSON omits CPU Stats even though individual runs may include them.
Additional Locations (1)
# Conflicts: # memtier_benchmark.cpp
| } | ||
| } | ||
| cpu_prev_tv = cpu_cur_tv; | ||
| cpu_history.push_back(cpu_snap); |
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CPU stats break across thread restarts
Medium Severity
Per-thread CPU tracking keeps thread_prev_cpu[t] keyed only by thread index, but worker threads can be join()ed and restart()ed with a different pthread_t. After a restart, deltas are computed against the previous thread’s CPU clock (or 0 if calls fail), producing incorrect per-thread CPU% and potentially spurious/missed >95% warnings.
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Summary
thread_infoon macOS,pthread_getcpuclockidon Linux)Details
A new
CPU Statssection is added to the JSON output underALL STATS, reporting per-second CPU percentages for the main thread and each worker thread. This helps users identify when memtier itself is the bottleneck rather than the server under test.Files changed
memtier_benchmark.cpp—get_thread_cpu_usec()helper + per-second CPU sampling in the benchmark looprun_stats.cpp/run_stats.h/run_stats_types.h—per_second_cpu_statsstruct and JSON serializationtests/test_cpu_stats.py— Three integration tests (structure, high-load, external validation)tests/test_requirements.txt— Addedpsutildependency for external validation testAGENTS.md/DEVELOPMENT.md— Documentation updatesTest plan
test_cpu_stats_in_json— Verifies CPU Stats appear in JSON with correct per-thread structuretest_cpu_stats_high_load— 500 clients on 1 thread; verifies non-trivial CPU and >95% warningtest_cpu_stats_external_validation— Cross-validates against psutil measurements (±15pp tolerance)pthread_getcpuclockidpath compiles🤖 Generated with Claude Code
Note
Medium Risk
Adds per-second CPU sampling in the main benchmark loop and emits new JSON/stderr output; main risk is measurement overhead and potential platform-specific differences (macOS Mach vs Linux pthread clocks) affecting performance and tests.
Overview
Adds per-second, per-thread CPU utilization reporting to the benchmark run and exposes it in JSON output under
ALL STATS→CPU Stats(including main thread and each worker thread).Implements OS-specific CPU time sampling (Mach on macOS,
pthread_getcpuclockidon Linux), stores samples inrun_stats, and prints a stderr warning when any worker exceeds 95% CPU.Introduces new integration coverage in
tests/test_cpu_stats.py(JSON structure checks, high-load warning/usage assertions, and optionalpsutilcross-validation) and documents the new testing/dependency requirements (addspsutiltotests/test_requirements.txt).Written by Cursor Bugbot for commit bff2e9c. This will update automatically on new commits. Configure here.