Intel® VTune™ Profiler

User Guide

Download PDF
ID 766319
Date 10/31/2024
Public
Document Table of Contents
Document Table of Contents x
User Guide
User Guide x
Introduction Install Intel® VTune™ Profiler Open Intel® VTune™ Profiler Set Up Project Set Up Analysis Target Analyze Performance Intel® VTune™ Profiler Command Line Interface API Support Troubleshooting Reference Notices and Disclaimers
Introduction x
Tuning Methodology Tutorials and Samples Notational Conventions Get Help Product Website and Support Related Information
Install Intel® VTune™ Profiler x
Sampling Drivers Set Up System for GPU Analysis Verify Intel® VTune™ Profiler Installation Install VTune Profiler Server Security Best Practices
Set Up System for GPU Analysis x
Rebuild and Install the Kernel for GPU Analysis Rebuild and Install Module i915 for GPU Analysis on CentOS* Rebuild and Install Module i915 for GPU Analysis on Ubuntu*
Install VTune Profiler Server x
Set Up Transport Security Configure User Authentication/Authorization
Open Intel® VTune™ Profiler x
Get Started with Intel® VTune™ Profiler Intel® VTune™ Profiler Graphical User Interface Web Server Interface Microsoft Visual Studio* Integration Eclipse* and Intel System Studio IDE Integration Containerization Support
Containerization Support x
Run VTune Profiler in a Container Profile Container Targets from the Host
Set Up Project x
WHERE: Analysis System WHAT: Analysis Target HOW: Analysis Types Search Directories
WHERE: Analysis System x
Analysis System Options
WHAT: Analysis Target x
Analysis Target Options
Search Directories x
Search Order
Set Up Analysis Target x
Prepare Application for Analysis Windows* Targets Linux* Targets Embedded Linux* Targets FreeBSD* Targets QNX* Targets Managed Code Targets Android* Targets Intel® Xeon Phi™ Processor Targets Targets in Virtualized Environments Targets in a Cloud Environment Arbitrary Targets Embedded System Targets
Windows* Targets x
Install the Sampling Drivers for Windows* Targets Debug Information for Windows* Application Binaries Compiler Switches for Performance Analysis on Windows* Targets Debug Information for Windows* System Libraries Add Administrative Privileges
Linux* Targets x
Build and Install the Sampling Drivers for Linux* Targets Debug Information for Linux* Application Binaries Compiler Switches for Performance Analysis on Linux* Targets Enable Linux* Kernel Analysis Resolution of Symbol Names for Linux-Loadable Kernel Modules Analyze Statically Linked Binaries on Linux* Targets Set Up Remote Linux* Target
Set Up Remote Linux* Target x
Set Up Linux* System for Remote Analysis Configure SSH Access for Remote Collection Search Directories for Remote Linux* Targets Temporary Directory for Performance Results on Linux* Targets
Embedded Linux* Targets x
Configure Yocto Project* and VTune Profiler with the Integration Layer Configure Yocto Project*/Wind River* Linux* and Intel® VTune™ Profiler with the Intel System Studio Integration Layer Configure Yocto Project* and Intel® VTune™ Profiler with the Linux* Target Package
FreeBSD* Targets x
Set Up FreeBSD* System
Managed Code Targets x
.NET* Targets Windows Store Application Targets Go* Application Targets
Android* Targets x
Build and Install Sampling Drivers for Android* Targets Set Up Android* System Enable Java* Analysis on Android* System Prepare an Android* Application for Analysis Analyze Unplugged Devices Search Directories for Android* Targets
Targets in Virtualized Environments x
Profile Targets on a VMware* Guest System Profile Targets on a Parallels* Guest System Profile Targets on a KVM* Guest System Profile Targets on a Xen* Virtualization Platform Profile Targets in the Hyper-V* Environment
Profile Targets on a KVM* Guest System x
Profile KVM Kernel Modules from the Host Profile KVM Kernel and User Space on the KVM System Profile KVM Kernel and User Space from the Host
Analyze Performance x
User-Mode Sampling and Tracing Collection Hardware Event-based Sampling Collection Performance Snapshot Algorithm Group Microarchitecture Analysis Group Parallelism Analysis Group Input and Output Analysis Accelerators Analysis Group Platform Analysis Group Platform Analysis Hybrid CPU Analysis Source Code Analysis Custom Analysis Energy Analysis Code Profiling Scenarios Control Data Collection Manage Data Views Manage Result Files
Hardware Event-based Sampling Collection x
Allow Multiple Runs or Multiplex Events Hardware Event-based Sampling Collection with Stacks Configure Stack Collection Analyze Performance Explore Parallelism See Also
Algorithm Group x
Hotspots Analysis for CPU Usage Issues Anomaly Detection Analysis (preview) Memory Consumption Analysis
Hotspots Analysis for CPU Usage Issues x
Hotspots View
Anomaly Detection Analysis (preview) x
Anomaly Detection View
Memory Consumption Analysis x
Memory Consumption and Allocations View
Microarchitecture Analysis Group x
Microarchitecture Exploration Analysis for Hardware Issues Memory Access Analysis for Cache Misses and High Bandwidth Issues
Microarchitecture Exploration Analysis for Hardware Issues x
Microarchitecture Exploration View Microarchitecture Pipe
Memory Access Analysis for Cache Misses and High Bandwidth Issues x
Memory Usage View
Parallelism Analysis Group x
Threading Analysis HPC Performance Characterization Analysis
Threading Analysis x
Threading Efficiency View
HPC Performance Characterization Analysis x
HPC Performance Characterization View
Input and Output Analysis x
Analyze Platform Performance Analyze DPDK Applications Analyze SPDK Applications Analyze Linux Kernel I/O
Accelerators Analysis Group x
GPU Offload Analysis GPU Compute/Media Hotspots Analysis (Preview) CPU/FPGA Interaction Analysis NPU Exploration Analysis
GPU Compute/Media Hotspots Analysis (Preview) x
GPU Compute/Media Hotspots View
CPU/FPGA Interaction Analysis x
CPU/FPGA Interaction View
NPU Exploration Analysis x
NPU Exploration View
Platform Analysis Group x
System Overview Analysis
System Overview Analysis x
Analyze Interrupts Analyze Latency Issues
Custom Analysis x
Custom Analysis Options
Custom Analysis Options x
Hardware Event List Linux* and Android* Kernel Analysis Sampling Interval Sample After Value
Hardware Event List x
Hardware Event Skid Instructions Retired Event Precise Events
Energy Analysis x
Run Energy Analysis View Energy Analysis Data with Intel® VTune™ Profiler Interpret Energy Analysis Data with Intel® VTune™ Profiler
Code Profiling Scenarios x
Java* Code Analysis Python* Code Analysis Intel® Threading Building Blocks Code Analysis MPI Code Analysis OpenSHMEM* Code Analysis with Fabric Profiler GPU Application Analysis on Intel® HD Graphics and Intel® Iris® Graphics Frame Data Analysis Task Analysis
GPU Application Analysis on Intel® HD Graphics and Intel® Iris® Graphics x
GPU OpenCL™ Application Analysis Intel® Media SDK Program Analysis
Control Data Collection x
Finalization Pause Data Collection Limit Data Collection Generate Command Line Configuration from GUI Minimize Collection Overhead Import External Data
Import External Data x
Use a Custom Collector Create a CSV File with External Data Import Linux Perf* Trace with VTune Profiler Metrics Examples of CSV Format and Imported Data
Manage Data Views x
Switch Viewpoints Control Window Synchronization View Stacks Manage Grid Views Manage Timeline View Change Threshold Values Choose Data Format Group and Filter Data View Data on Inline Functions Analyze Loops Stitch Stacks for Intel® oneAPI Threading Building Blocks or OpenMP* Analysis Search for Data
View Stacks x
Call Stack Mode Metrics Distribution Over Call Stacks
Manage Result Files x
VTune Profiler Filenames and Locations Import Results and Traces into VTune Profiler GUI Compare Results
Compare Results x
Compare Source Code View Comparison Data
View Comparison Data x
Comparison Summary Bottom-up Comparison Top-down Tree Comparison
Intel® VTune™ Profiler Command Line Interface x
vtune Command Syntax vtune Actions Run Command Line Analysis Work with Results from Command Line Generate Command Line Reports Command Line Usage Scenarios Command Line Interface Reference Report Problems from Command Line
Run Command Line Analysis x
performance-snapshot Command Line Analysis hotspots Command Line Analysis anomaly-detection Command Line Analysis threading Command Line Analysis memory-consumption Command Line Analysis hpc-performance Command Line Analysis uarch-exploration Command Line Analysis memory-access Command Line Analysis tsx-exploration Command Line Analysis tsx-hotspots Command Line Analysis sgx-hotspots Command Line Analysis gpu-hotspots Command Line Analysis gpu-offload Command Line Analysis npu graphics-rendering Command Line Analysis fpga-interaction Command Line Analysis io Command Line Analysis system-overview Command Line Analysis runsa/runss Custom Command Line Analysis Configure Analysis Options from Command Line
Configure Analysis Options from Command Line x
Collect System-Wide Data from Command Line Collect Data on Remote Linux* Systems from Command Line Configure GPU Analysis from Command Line Specify Search Directories from Command Line Specify Result Directory from Command Line Pause Collection from Command Line Manage Analysis Duration from Command Line Limit Data Collection from Command Line
Work with Results from Command Line x
View Command Line Results in the GUI Import Results from Command Line Re-finalize Results from Command Line
Generate Command Line Reports x
Summary Report Hotspots Report Hardware Events Report Callstacks Report Timeline Report Top-down Report GPU Compute/Media Hotspots Report gprof-cc Report Difference Report View Source Objects from Command Line Save and Format Command Line Reports Filter and Group Command Line Reports
Command Line Usage Scenarios x
Use VTune Profiler Server in Containers Android* Target Analysis from the Command Line OpenMP* Analysis from the Command Line Java* Code Analysis from the Command Line
Command Line Interface Reference x
Option Descriptions and General Rules allow-multiple-runs analyze-kvm-guest analyze-system app-working-dir archive call-stack-mode collect collect-with column command cpu-mask csv-delimiter cumulative-threshold-percent custom-collector data-limit discard-raw-data duration filter finalization-mode finalize format group-by help import inline-mode knob kvm-guest-kallsyms kvm-guest-modules limit loop-mode mrte-mode no-follow-child no-summary no-unplugged-mode quiet report report-knob report-output report-width result-dir resume-after return-app-exitcode ring-buffer search-dir show-as sort-asc sort-desc source-object source-search-dir stack-size start-paused strategy target-install-dir target-system target-tmp-dir target-duration-type target-pid target-process time-filter trace-mpi user-data-dir verbose version
API Support x
Support for Instrumentation and Tracing Technology API (ITT API) JIT Profiling API System APIs Supported by Intel® VTune™ Profiler
Support for Instrumentation and Tracing Technology API (ITT API) x
Basic Usage and Configuration Instrumentation and Tracing Technology API Reference
Basic Usage and Configuration x
Configure Your Build System Attach ITT APIs to a Launched Application Instrument Your Application Minimize ITT API Overhead View Instrumentation and Tracing Technology (ITT) API Task Data in Intel® VTune™ Profiler
Instrumentation and Tracing Technology API Reference x
Domain API String Handle API Collection Control API Thread Naming API Task API Frame API Histogram API User-Defined Synchronization API Event API Counter API Context Metadata API Load Module API Memory Allocation APIs
JIT Profiling API x
Using JIT Profiling API JIT Profiling API Reference
JIT Profiling API Reference x
iJIT_NotifyEvent iJIT_IsProfilingActive iJIT_ GetNewMethodID
Troubleshooting x
Best Practices: Resolve Intel® VTune™ Profiler BSODs, Crashes, and Hangs in Windows* OS Error Message: Application Sets Its Own Handler for Signal Error Message: Cannot Enable Event-Based Sampling Collection Error Message: Cannot Collect GPU Hardware Metrics Error Message: Cannot Load Data File Error Message: Cannot Locate Debugging Information Error Message: Cannot Open Data Error Message: Client Is Not Authorized to Connect to Server Error Message: Root Privileges Required for Processor Graphics Events Error Message: No Pre-built Driver Exists for This System Error Message: Not All OpenCL™ API Profiling Callbacks Are Received Error Message: Problem Accessing the Sampling Driver Error Message: Required Key Not Available Error Message: Scope of ptrace System Call Is Limited Error Message: Stack Size Is Too Small Error Message: Symbol File Is Not Found Problem: Analysis of the .NET* Application Fails Problem: Cannot Access VTune Profiler Documentation Problem: CPU time for Hotspots or Threading Analysis is Too Low Problem: 'Events= Sample After Value (SAV) * Samples' Is Not True If Multiple Runs Are Disabled Problem: Guessed Stack Frames Problem: GUI Hangs or Crashes Problem: Inaccurate Sum in the Grid Problem: Information Collected via ITT API Is Not Available When Attaching to a Process Problem: No GPU Utilization Data Is Collected Problem: Same Functions Are Compared As Different Instances Problem: Skipped Stack Frames Problem: Stack in the Top-Down Tree Window Is Incorrect Problem: Stacks in Call Stack and Bottom-Up Panes Are Different Problem: System Functions Appear in the User Functions Only Mode Problem: Intel® VTune™ Profiler is Slow to Respond When Collecting or Displaying Data Problem: Intel® VTune™ Profiler is Slow on X-Servers with SSH Connection Problem: Unexpected Paused Time Problem: {Unknown Timer} in the Platform Power Analysis Viewpoint Problem: Unknown Critical Error Due to Disabled Loopback Interface Problem: Unknown Frames Problem: Unsupported Microsoft* Windows* OS
Reference x
User Interface Reference CPU Metrics Reference GPU Metrics Reference OpenCL™ Kernel Analysis Metrics Reference Energy Analysis Metrics Reference Intel Processor Events Reference
User Interface Reference x
Context Menu: Grid Context Menus: Call Stack Pane Context Menus: Project Navigator Context Menus: Source/Assembly Window Dialog Box: Binary/Symbol Search Dialog Box: Source Search Hot Keys Menu: Customize Grouping Menu: Intel VTune Profiler Pane: Call Stack Pane: Options - General Pane: Options - Result Location Pane: Options - Source/Assembly Project Navigator Pane: Timeline Toolbar: Configure Analysis Toolbar: Filter Toolbar: Source/Assembly Toolbar: Intel VTune Profiler Window: Bandwidth - Platform Power Analysis Window: Bottom-up Window: Caller/Callee Window: Cannot Find <file type> File Window: Collection Log Window: Compare Results Window: Configure Analysis Window: Core Wake-ups - Platform Power Analysis Window: Correlate Metrics - Platform Power Analysis Window: CPU C/P States - Platform Power Analysis Window: Debug Window: Event Count - Hardware Events Window: Flame Graph Window: Graphics - GPU Compute/Media Hotspots Window: Graphics C/P States - Platform Power Analysis Window: NC Device States - Platform Power Analysis Window: Platform Window: Platform Power Analysis Window: Sample Count - Hardware Events Window: SC Device States - Platform Power Analysis Window: Summary Window: System Sleep States - Platform Power Analysis Window: Temperature/Thermal Sample - Platform Power Analysis Window: Timer Resolution - Platform Power Analysis Window: Top-down Tree Window: Uncore Event Count - Hardware Events Window: Wakelocks - Platform Power Analysis
Window: Summary x
Window: Summary - Input and Output Summary Window: Summary - Microarchitecture Exploration Window: Summary - GPU Analysis Window: Summary - Hardware Events Window: Summary - Hotspots by CPU Utilization Window: Summary - HPC Performance Characterization Window: Summary - Memory Consumption Window: Summary - Memory Usage Window: Summary - Platform Power Analysis
GPU Metrics Reference x
ALU0 Active ALU0 Instructions ALU1 Active ALU1 Instructions ALU2 Active ALU2 Instructions ALU0 and ALU1 Active ALU0 and ALU2 Active ALU0 and XMX Utilization Average Time Computing Threads Started Computing Threads Started, Threads/sec CPU Time EU 2 FPU Pipelines Active EU Array Active EU Array Idle EU Array Stalled/Idle EU Array Stalled EU IPC Rate EU Send pipeline active EU Threads Occupancy Global GPU EU Array Usage GPU Instruction Cache L3 Miss Ratio GPU L3 Atomics GPU L3 Bound GPU L3 Miss Ratio GPU L3 Misses GPU L3 Misses, Misses/sec GPU Load Store Cache Miss Ratio GPU Load Store Cache L3 Miss Ratio GPU LSC Atomics GPU LSC Fences GPU Media Read Requests GPU Media Write Requests GPU SLM Atomics GPU SLM Fences GPU Memory Read Bandwidth, GB/sec GPU Memory Texture Read Bandwidth, GB/sec GPU Memory Write Bandwidth, GB/sec GPU Sampler L3 Miss Ratio GPU Texel Quads Count, Count/sec GPU Utilization Graphics Security Controller Busy Host to GPU Memory Read Bandwidth Host-to-GPU Memory Write Bandwidth Instance Count Instruction Cache Miss Ratio L3 Busy L3 Input Available L3 Instruction Cache Bandwidth L3 Load Store Cache Read Bandwidth L3 Load Store Cache Write Bandwidth L3 Miss Ratio L3 Output Ready L3 Read Bandwidth L3 SQ Full L3 Stalled L3 Write Bandwidth L3 Sampler Bandwidth, GB/sec L3 Shader Bandwidth, GB/sec LLC Miss Rate due GPU Lookups LLC Miss Ratio due GPU Lookups LSC Input Available LSC Output Ready LSC Partial Writes Local Maximum GPU Utilization Multiple Pipe Utilization Occupancy PS EU Active % PS EU Stall % Ratio to Max Bandwidth, % Ratio to Max Bandwidth, % Ratio to Max Bandwidth, % Render/GPGPU Command Streamer Loaded Sampler Input Available Sampler Output Ready Samples Blended Samples Killed in PS, pixels Samples Written Sampler Busy Sampler Is Bottleneck Shared Local Memory Read Bandwidth, GB/sec Shared Local Memory Write Bandwidth, GB/sec SIMD Width SLM Bank Conflicts Stack-to-stack Incoming Bandwidth Stack-to-stack Outgoing Bandwidth System Memory Read Bandwidth System Memory Write Bandwidth Size Total, GB/sec Thread Dispatcher Active TLB Misses Total Time Typed Memory Read Bandwidth, GB/sec Typed Memory Write Bandwidth, GB/sec Typed Reads Coalescence Typed Writes Coalescence Untyped Memory Read Bandwidth, GB/sec Untyped Memory Write Bandwidth, GB/sec Untyped Reads Coalescence Untyped Writes Coalescence Video Codec Busy Video Codec Read Requests Video Codec Write Requests Video Codec 2 Busy Video Codec 2 Read Requests Video Codec 2 Write Requests Video Enhancement Busy Video Enhancement Read Requests Video Enhancement Write Requests Video Enhancement 2 Busy Video Enhancement 2 Read Requests Video Enhancement 2 Write Requests VS EU Active VS EU Stall XVE Barrier Stall XVE Bit Manipulation Instructions XVE Control Stall XVE Dist or Acc Stall XVE INT16\INT32\INT64\FP16\FP32\FP64 Instructions XVE FP16\BF16\INT8\INT4\INT2 XMX Instructions XVE Instruction Fetch Stall XVE Pipe Stall XVE Send Stall XVE SBID Stall XVE XMX Instructions XVE XMX Pipeline Active
OpenCL™ Kernel Analysis Metrics Reference x
Computing Task Total Time Instance Count SIMD Width SIMD Utilization Work Size
Energy Analysis Metrics Reference x
Available Core Time C-State D0ix States DRAM Self Refresh Energy Consumed (mJ) Idle Wake-ups P-State S0ix States Temperature Timer Resolution Total Time in C0 State Total Time in Non-C0 States Total Time in S0 State Total Wake-up Count Wake-ups Wake-ups/sec per Core
User Guide

Hardware Event-based Sampling Collection with Stacks

Configure the event-based sampling collector to analyze call stacks for your functions and identify performance, parallelism and power consumption issues.

NOTE:

For Linux* targets, make sure your kernel is configured to support event-based stack sampling collection.

Multitask operating systems execute all software threads in time slices (thread execution quanta). Intel® VTune™ Profiler profiler handles thread quantum switches and performs all monitoring operations in correlation with the thread quantum layout.

The figure below explains the general idea of per-thread quantum monitoring:

  • The profiler gains control whenever a thread gets scheduled on and then off a processor (that is, at thread quantum borders). That enables the profiler to take exact measurements of any hardware performance events or timestamps, as well as collect a call stack to the point where the thread gets activated and inactivated.

  • The profiler determines a reason for thread inactivation: it can either be an explicit request for synchronization , or a so-called thread quantum expiration, when the operating system scheduler preempts the current thread to run another, higher-priority one instead.

  • The time during which a thread remains inactive is also measured directly and differentiated based on the thread inactivation reason: inactivity caused by a request for synchronization is called Wait time, while inactivity caused by preemption is called Inactive time.

While a thread is active on a processor (inside a quantum), the profiler employs event-based sampling to reconstruct the program logic and associate hardware events and other characteristics with the program code. Unlike the traditional event-based sampling, the profiler upon each sampling interrupt also collects:

  • call stack information

  • branching information (if configured so)

  • processor timestamps

All that allows for statistically reconstructing program execution logic (call and control flow graphs) and tracing threading activity over time, as well as collecting virtually any information related to hardware utilization and performance.

Configure Stack Collection

  1. Click the Configure Analysis button on the VTune Profiler toolbar.

    The Configure Analysis window opens.

  2. Specify your analysis system in the WHERE pane and your analysis target in the WHAT pane.

  3. In the HOW pane, choose the required event-based sampling analysis type. Typically, you are recommended to start with the Hotspots analysis in the hardware event-based sampling mode.

  4. Configure collection options, if required. For call stack analysis, consider enabling the Collect stacks option.

  5. Click the Start button at the bottom to run the selected analysis type.

    VTune Profiler collects hardware event-based sampling data along with the information on execution paths. You may see the collected results in the Hardware Events viewpoint providing performance, parallelism and power consumption data on detected call paths.

NOTE:

  • The event-based stack sampling data collection cannot be configured for the entire system. You have to specify an application to launch or attach to.

  • By default, on Linux* systems, VTune Profiler uses the driverless Perf*-based mode for hardware event-based collection with stacks. To use the driver-based mode, set the Stack size option to 0 (unlimited).

  • Call stack analysis adds an overhead to your data collection. To minimize the overhead incurred with the stack size, use the Stack size option in the custom hardware event-based sampling configuration or -stack-size knob from CLI to limit the size of a raw stack. By default, on Linux a stack size of 1024 bytes is collected. On Windows, by default, a full size stack is collected (zero size value). If you disable this option, the overhead will be also reduced but no stack data will be collected.

Analyze Performance

Select the Hardware Events viewpoint and click the Event Count tab. By default, the data in the grid are sorted by the Clockticks (CPU_CLK_UNHALTED) event count providing primary hotspots on top of the list.

Click the plus sign to expand each hotspot node (a function, by default) into a series of call paths, along which the hotspot was executed. VTune Profiler decomposes all hardware events per call path based on the frequency of the path execution.

The counts of the hardware events of all execution paths leading to a sampled node sum up to the event count of that node. For example, for the CpupSyscallStub function, which is the top hotspot of the application, the INST_RETIRED.ANY event count equals the sum of event counts for all 5 calling sequences: 25 700 419 203.

Such a decomposition is extremely important if a hotspot is in a third-party library function whose code cannot be modified, or whose behavior depends on input parameters. In this case the only way of optimization is analyzing the callers and eliminating excessive invocations of the function, or learning which parameters/conditions cause most of the performance degradation.

Explore Parallelism

When the call stacks collection is enabled (for example, Collect stacks option for the Hotspots in the hardware event-based sampling mode), the VTune Profiler analyzes context switches and displays data on the threads activity using the context switch performance metrics.

Click the Context Switch by Reason > Synchronization column header to sort the data by this metric. The synchronization hotspots with the highest number of context switches and high Wait time values typically signals a thread contention on this stack.

Select a context switch oriented type of the stack (for example, the Preemption Context Switch Count type) in the drop-down menu of the Call Stack pane and explore the Timeline pane that shows each separate thread execution quantum. A dark-green bar represents a single thread activity quantum, grey bars and light-green bars - thread inactivity periods (context switches). Hover over a context switch region in the Timeline pane to view details on its duration, start time and the reason of thread inactivity.

When you select a context switch region in the Timeline pane, the Call Stack pane displays a call sequence at which a preceding quantum was interrupted.

You may also select a hardware or software event from the Timeline drop-down menu and see how the event maps to the thread activity quanta (or to the inactivity periods).

Correlate data you obtained during the performance and parallelism analysis. Those execution paths that are listed as the performance hotspots with the highest event count and as the synchronization hotspots are obvious candidates for optimization. Your next step could be analyzing power metrics to understand the cost of such a synchronization scheme in terms of energy.

NOTE:

  • For analyses using the Perf*-based driverless collection, the types of context switches (preemption or synchronization) may not be identified on kernels older than 4.17 and the following metrics may not be available: Wait time, Wait Rate, Inactive Time, Preemption and Synchronization Context Switch Count.

  • The speed at which the data is generated (proportional to the sampling frequency and the intensity of thread synchronization/contention) may become greater than the speed at which the data is being saved to a trace file, so the profiler will try to adapt the incoming data rate to the outgoing data rate by not letting threads of a program being profiled be scheduled for execution. This will cause paused regions to appear on the timeline, even if no pause was explicitly requested. In ultimate cases, when this procedure fails to limit the incoming data rate, the profiler will begin losing sample records, but will still keep the counts of hardware events. If such a situation occurs, the hardware event counts of lost sample records will be attributed to a special node: [Events Lost on Trace Overflow].

Parent topic: Hardware Event-based Sampling Collection
Level Two Title