RUM-16039: Upgrade Mach profiler sampler to sample CPU-time

Author: simaoseica-dd

BenchmarkTests/Runner/Scenarios/Profiling/ProfilingScenario.swift

@@ -32,6 +32,12 @@ struct ProfilingScenario: Scenario {
 
         RUMMonitor.shared().addAttribute(forKey: "scenario", value: "ContinuousProfiling")
 
-        Profiling.enable(with: .init(applicationLaunchSampleRate: .maxSampleRate, continuousSampleRate: .maxSampleRate))
+        Profiling.enable(
+            with: .init(
+                applicationLaunchSampleRate: .maxSampleRate,
+                continuousSampleRate: .maxSampleRate,
+                featureFlags: [.cpuTimeSamples: true]
+            )
+        )
     }
 }

DatadogProfiling/Mach/dd_pprof.cpp

@@ -17,8 +17,12 @@
 extern "C" {
 
 dd_pprof_t* dd_pprof_create(uint64_t sampling_interval_ns) {
+    return dd_pprof_create_with_cpu_time(sampling_interval_ns, false);
+}
+
+dd_pprof_t* dd_pprof_create_with_cpu_time(uint64_t sampling_interval_ns, bool record_cpu_time) {
     try {
-        auto* profiler = new dd::profiler::profile(sampling_interval_ns);
+        auto* profiler = new dd::profiler::profile(sampling_interval_ns, record_cpu_time);
         return reinterpret_cast<dd_pprof_t*>(profiler);
     } catch (...) {
         return nullptr;

DatadogProfiling/Mach/dd_profiler.cpp

@@ -155,6 +155,23 @@ static double read_profiling_sample_rate() {
     return sample_rate;
 }
 
+static bool read_profiling_record_cpu_time() {
+    CFStringRef suiteName = CFSTR(DD_PROFILING_USER_DEFAULTS_SUITE_NAME);
+    CFStringRef key = CFSTR(DD_PROFILING_RECORD_CPU_TIME_KEY);
+    CFPropertyListRef value = CFPreferencesCopyAppValue(key, suiteName);
+
+    bool result = false;
+
+    if (value) {
+        if (CFGetTypeID(value) == CFBooleanGetTypeID()) {
+            result = CFBooleanGetValue((CFBooleanRef)value);
+        }
+        CFRelease(value);
+    }
+
+    return result;
+}
+
 /**
  * Deletes the DatadogProfiling defaults from the `UserDefaults`
  * to be re-evaluated during `Profiling.enable()`.
@@ -163,9 +180,11 @@ void dd_delete_profiling_defaults() {
     CFStringRef suiteName = CFSTR(DD_PROFILING_USER_DEFAULTS_SUITE_NAME);
     CFStringRef isEnabledKey = CFSTR(DD_PROFILING_IS_ENABLED_KEY);
     CFStringRef sampleRateKey = CFSTR(DD_PROFILING_APP_LAUNCH_SAMPLE_RATE_KEY);
+    CFStringRef recordCPUTimeKey = CFSTR(DD_PROFILING_RECORD_CPU_TIME_KEY);
 
     CFPreferencesSetValue(isEnabledKey, NULL, suiteName, kCFPreferencesCurrentUser, kCFPreferencesAnyHost);
     CFPreferencesSetValue(sampleRateKey, NULL, suiteName, kCFPreferencesCurrentUser, kCFPreferencesAnyHost);
+    CFPreferencesSetValue(recordCPUTimeKey, NULL, suiteName, kCFPreferencesCurrentUser, kCFPreferencesAnyHost);
     CFPreferencesSynchronize(suiteName, kCFPreferencesCurrentUser, kCFPreferencesAnyHost);
 }
 
@@ -353,7 +372,9 @@ class dd_profiler {
 
         if (profiler) return true;
 
-        profile = new (std::nothrow) dd::profiler::profile(sampling_interval_ns);
+        record_cpu_time = read_profiling_record_cpu_time();
+
+        profile = new (std::nothrow) dd::profiler::profile(sampling_interval_ns, record_cpu_time);
         if (!profile) {
             status = DD_PROFILER_STATUS_ALLOCATION_FAILED;
             return false;
@@ -362,6 +383,7 @@ class dd_profiler {
 
         sampling_config_t config = SAMPLING_CONFIG_DEFAULT;
         config.sampling_interval_nanos = sampling_interval_ns;
+        config.record_cpu_time = record_cpu_time ? 1 : 0;
 
         profiler = new (std::nothrow) mach_sampling_profiler(&config, callback, this, hard_limit_bytes);
         if (!profiler) {
@@ -383,6 +405,7 @@ class dd_profiler {
     uint64_t hard_limit_bytes = DD_PROFILER_DEFAULT_HARD_LIMIT_BYTES;
     uint64_t sampling_interval_ns = SAMPLING_CONFIG_DEFAULT_INTERVAL_NANOS;
     int64_t server_time_offset_ns = 0;
+    bool record_cpu_time = false;
 
     /**
      * Mutex protecting the profile pointer.

DatadogProfiling/Mach/include/dd_pprof.h

@@ -42,6 +42,15 @@ typedef struct profile dd_pprof_t;
  */
 dd_pprof_t* dd_pprof_create(uint64_t sampling_interval_ns);
 
+/**
+ * Create a new pprof profile aggregator with optional CPU-time sample values.
+ *
+ * @param sampling_interval_ns The sampling interval in nanoseconds
+ * @param record_cpu_time Whether samples should include CPU time as a second value
+ * @return Pointer to the created profile, or NULL on failure
+ */
+dd_pprof_t* dd_pprof_create_with_cpu_time(uint64_t sampling_interval_ns, bool record_cpu_time);
+
 /**
  * Destroy a pprof profile aggregator and free all associated memory
  *

DatadogProfiling/Mach/include/dd_profiler.h

@@ -52,6 +52,8 @@ typedef struct stack_trace {
     uint64_t timestamp;
     /** Actual sampling interval in nanoseconds for this sample */
     uint64_t sampling_interval_nanos;
+    /** CPU time consumed by this thread since the previous sample */
+    uint64_t cpu_time_nanos;
     /** The stack frames array */
     stack_frame_t* frames;
     /** Number of frames in the trace */
@@ -74,6 +76,8 @@ typedef struct sampling_config {
     uint32_t max_thread_count;  // default: 100
     /** QoS class for the sampling thread */
     qos_class_t qos_class;
+    /** Whether samples should include a CPU-time value */
+    uint8_t record_cpu_time;
 } sampling_config_t;
 
 /**
@@ -100,7 +104,8 @@ static const sampling_config_t SAMPLING_CONFIG_DEFAULT = {
     SAMPLING_CONFIG_DEFAULT_BUFFER_SIZE,     // max_buffer_size
     SAMPLING_CONFIG_DEFAULT_STACK_DEPTH,     // max_stack_depth
     SAMPLING_CONFIG_DEFAULT_THREAD_COUNT,    // max_thread_count
-    QOS_CLASS_USER_INTERACTIVE               // qos_class
+    QOS_CLASS_USER_INTERACTIVE,              // qos_class
+    0                                        // record_cpu_time
 };
 
 /**
@@ -122,6 +127,7 @@ typedef void (*stack_trace_callback_t)(stack_trace_t* traces, size_t count, void
 #define DD_PROFILING_USER_DEFAULTS_SUITE_NAME "com.datadoghq.ios-sdk.profiling"
 #define DD_PROFILING_IS_ENABLED_KEY "is_profiling_enabled"
 #define DD_PROFILING_APP_LAUNCH_SAMPLE_RATE_KEY "profiling_app_launch_sample_rate"
+#define DD_PROFILING_RECORD_CPU_TIME_KEY "profiling_record_cpu_time"
 
 #ifdef __cplusplus
 

DatadogProfiling/Mach/include/mach_sampling_profiler.h

@@ -21,6 +21,7 @@
 #include <memory>
 #include <mutex>
 #include <pthread.h>
+#include <unordered_map>
 #include <vector>
 
 #ifdef __cplusplus
@@ -165,13 +166,23 @@ class mach_sampling_profiler {
      * @param thread The thread to sample
      * @param interval_nanos The actual sampling interval in nanoseconds for this sample
      */
-    void sample_thread(thread_t thread, uint64_t interval_nanos);
+    void sample_thread(thread_t thread, uint64_t interval_nanos, uint64_t cpu_time_nanos);
 
     /**
      * @brief Returns true when the thread is owned by the profiler itself.
      */
     bool is_profiler_internal_thread(thread_t thread) const;
 
+    /**
+     * @brief Returns CPU time consumed since the previous observation for this thread.
+     */
+    uint64_t thread_cpu_time_delta_nanos(thread_t thread);
+
+    /**
+     * @brief Removes CPU-time state for threads no longer present in the task.
+     */
+    void prune_thread_cpu_time_state(const thread_t* threads, mach_msg_type_number_t count);
+
 private:
     /**
      * @brief Static entry point for the sampling thread
@@ -184,6 +195,7 @@ class mach_sampling_profiler {
     std::mutex state_mutex;
     /// Indicates whether `sampling_thread` currently refers to a live session thread.
     std::atomic<bool> has_sampling_thread{false};
+    std::unordered_map<thread_t, uint64_t> previous_thread_cpu_time_nanos;
 };
 
 } // namespace dd::profiler

DatadogProfiling/Mach/include/profile.h

@@ -147,7 +147,7 @@ class profile {
      * @brief Construct a new profile aggregator
      * @param sampling_interval_ns Sampling interval in nanoseconds
      */
-    explicit profile(uint64_t sampling_interval_ns);
+    explicit profile(uint64_t sampling_interval_ns, bool record_cpu_time = false);
     ~profile() = default;
 
     profile(const profile&) = delete;
@@ -189,10 +189,16 @@ class profile {
 
     /** @brief Get cached string ID for "wall-time" */
     uint32_t wall_time_str_id() const { return _wall_time_str_id; }
+
+    /** @brief Get cached string ID for "cpu-time" */
+    uint32_t cpu_time_str_id() const { return _cpu_time_str_id; }
 
     /** @brief Get cached string ID for "nanoseconds" */
     uint32_t nanoseconds_str_id() const { return _nanoseconds_str_id; }
 
+    /** @brief Whether samples include a CPU-time value in addition to wall-time */
+    bool cpu_time_enabled() const { return _record_cpu_time; }
+
     /** @brief Number of labels exported for the sample */
     size_t label_count(const sample_t& sample) const { return sample.labels.size() + 1; }
 
@@ -238,12 +244,18 @@ class profile {
 
     /** @brief Profile sampling interval in nanoseconds */
     uint64_t _sampling_interval_ns;
+
+    /** @brief Whether samples include CPU time as a second value */
+    bool _record_cpu_time;
 
     /** @brief Cached string ID for empty string */
     uint32_t _empty_str_id;
 
     /** @brief Cached string ID for "wall-time" */
     uint32_t _wall_time_str_id;
+
+    /** @brief Cached string ID for "cpu-time" */
+    uint32_t _cpu_time_str_id;
 
     /** @brief Cached string ID for "nanoseconds" */
     uint32_t _nanoseconds_str_id;

DatadogProfiling/Mach/mach_sampling_profiler.cpp

@@ -19,6 +19,7 @@
 #include <setjmp.h>
 #include <mach/thread_act.h>
 #include <mach/thread_status.h>
+#include <mach/thread_info.h>
 #include <mach/machine/thread_state.h>
 #include <new>
 #include <utility>
@@ -160,11 +161,32 @@ bool stack_trace_init(stack_trace_t* trace, uint32_t max_depth, uint64_t interva
     trace->thread_name = nullptr;
     trace->timestamp = 0;
     trace->sampling_interval_nanos = interval_nanos;
+    trace->cpu_time_nanos = 0;
     trace->frame_count = 0;
     trace->frames = (stack_frame_t*)malloc(max_depth * sizeof(stack_frame_t));
     return trace->frames != nullptr;
 }
 
+static bool thread_cpu_time_nanos(thread_t thread, uint64_t* cpu_time_nanos) {
+    if (!cpu_time_nanos) return false;
+
+    thread_basic_info_data_t info{};
+    mach_msg_type_number_t count = THREAD_BASIC_INFO_COUNT;
+    if (thread_info(thread, THREAD_BASIC_INFO, reinterpret_cast<thread_info_t>(&info), &count) != KERN_SUCCESS) {
+        return false;
+    }
+
+    const uint64_t user_time_nanos =
+        (static_cast<uint64_t>(info.user_time.seconds) * 1000000000ULL)
+        + (static_cast<uint64_t>(info.user_time.microseconds) * 1000ULL);
+    const uint64_t system_time_nanos =
+        (static_cast<uint64_t>(info.system_time.seconds) * 1000000000ULL)
+        + (static_cast<uint64_t>(info.system_time.microseconds) * 1000ULL);
+
+    *cpu_time_nanos = user_time_nanos + system_time_nanos;
+    return true;
+}
+
 /**
  * Destroys a stack trace, freeing the thread name and frames array.
  * 
@@ -396,6 +418,7 @@ bool mach_sampling_profiler::start_sampling() {
 
     // Clear any leftover data from previous runs
     sample_buffer.clear();
+    previous_thread_cpu_time_nanos.clear();
     if (sample_buffer.capacity() < config.max_buffer_size) {
         sample_buffer.reserve(config.max_buffer_size);
     }
@@ -491,9 +514,10 @@ bool mach_sampling_profiler::is_profiler_internal_thread(thread_t thread) const
  * @param thread The thread to sample
  * @param interval_nanos The actual sampling interval in nanoseconds for this sample
  */
-void mach_sampling_profiler::sample_thread(thread_t thread, uint64_t interval_nanos) {
+void mach_sampling_profiler::sample_thread(thread_t thread, uint64_t interval_nanos, uint64_t cpu_time_nanos) {
     stack_trace_t trace;
     if (!stack_trace_init(&trace, config.max_stack_depth, interval_nanos)) return;
+    trace.cpu_time_nanos = cpu_time_nanos;
 
     // Get thread info
     stack_trace_get_thread_info(&trace, thread);
@@ -519,6 +543,53 @@ void mach_sampling_profiler::sample_thread(thread_t thread, uint64_t interval_na
     }
 }
 
+uint64_t mach_sampling_profiler::thread_cpu_time_delta_nanos(thread_t thread) {
+    if (!config.record_cpu_time) {
+        return 0;
+    }
+
+    uint64_t current_cpu_time_nanos = 0;
+    if (!thread_cpu_time_nanos(thread, &current_cpu_time_nanos)) {
+        return 0;
+    }
+
+    auto result = previous_thread_cpu_time_nanos.emplace(thread, current_cpu_time_nanos);
+    if (result.second) {
+        return 0;
+    }
+
+    const uint64_t previous_cpu_time_nanos = result.first->second;
+    result.first->second = current_cpu_time_nanos;
+
+    if (current_cpu_time_nanos < previous_cpu_time_nanos) {
+        return 0;
+    }
+
+    return current_cpu_time_nanos - previous_cpu_time_nanos;
+}
+
+void mach_sampling_profiler::prune_thread_cpu_time_state(const thread_t* threads, mach_msg_type_number_t count) {
+    if (!config.record_cpu_time || previous_thread_cpu_time_nanos.empty()) {
+        return;
+    }
+
+    for (auto it = previous_thread_cpu_time_nanos.begin(); it != previous_thread_cpu_time_nanos.end();) {
+        bool is_live_thread = false;
+        for (mach_msg_type_number_t i = 0; i < count; i++) {
+            if (threads[i] == it->first) {
+                is_live_thread = true;
+                break;
+            }
+        }
+
+        if (is_live_thread) {
+            ++it;
+        } else {
+            it = previous_thread_cpu_time_nanos.erase(it);
+        }
+    }
+}
+
 /**
  * Main sampling loop that collects stack traces from threads.
  */
@@ -535,7 +606,8 @@ void mach_sampling_profiler::main() {
         }
 
         if (config.profile_current_thread_only) {
-            sample_thread(pthread_mach_thread_np(target_thread), interval_nanos);
+            const thread_t thread = pthread_mach_thread_np(target_thread);
+            sample_thread(thread, interval_nanos, thread_cpu_time_delta_nanos(thread));
             if (sample_buffer.size() >= config.max_buffer_size) {
                 worker->enqueue_active_buffer(sample_buffer);
             }
@@ -557,13 +629,15 @@ void mach_sampling_profiler::main() {
                 // Skip profiler-owned threads to avoid self-noise in customer profiles.
                 if (is_profiler_internal_thread(threads[i])) continue;
 
-                sample_thread(threads[i], interval_nanos);
+                sample_thread(threads[i], interval_nanos, thread_cpu_time_delta_nanos(threads[i]));
 
                 if (sample_buffer.size() >= config.max_buffer_size) {
                     worker->enqueue_active_buffer(sample_buffer);
                 }
             }
 
+            prune_thread_cpu_time_state(threads, count);
+
             // Clean up thread references
             for (mach_msg_type_number_t i = 0; i < count; i++) {
                 mach_port_deallocate(mach_task_self(), threads[i]);

DatadogProfiling/Mach/profile.cpp

@@ -81,8 +81,9 @@ std::string uuid_string(const uuid_t uuid) {
  * 
  * @param sampling_interval_ns Sampling interval in nanoseconds
  */
-profile::profile(uint64_t sampling_interval_ns) 
+profile::profile(uint64_t sampling_interval_ns, bool record_cpu_time)
     : _sampling_interval_ns(sampling_interval_ns)
+    , _record_cpu_time(record_cpu_time)
     , _epoch_offset(uptime_epoch_offset())
     , _server_time_offset_ns(0)
     , _start_timestamp(0)
@@ -95,6 +96,7 @@ profile::profile(uint64_t sampling_interval_ns)
     // Pre-intern common strings for performance
     _empty_str_id = intern_string("");
     _wall_time_str_id = intern_string("wall-time");
+    _cpu_time_str_id = _record_cpu_time ? intern_string("cpu-time") : 0;
     _nanoseconds_str_id = intern_string("nanoseconds");
     _end_timestamp_ns_str_id = intern_string("end_timestamp_ns");
     _thread_id_str_id = intern_string("thread id");
@@ -176,6 +178,9 @@ void profile::add_samples(const stack_trace_t* traces, size_t count, binary_imag
         sample.timestamp_uptime_ns = trace.timestamp;
         sample.labels = std::move(labels);
         sample.values = {static_cast<int64_t>(trace.sampling_interval_nanos)};
+        if (_record_cpu_time) {
+            sample.values.push_back(static_cast<int64_t>(trace.cpu_time_nanos));
+        }
 
         _samples.push_back(std::move(sample));