gpu-hotspots Command Line Analysis

User Guide

Intel® VTune™ Profiler User Guide

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ID 766319

Date 12/16/2022

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gpu-hotspots Command Line Analysis

Use the gpu-hotspots value to launch the GPU Compute/Media Hotspots analysis to:

Explore GPU kernels with high GPU utilization, estimate the effectiveness of this utilization, identify possible reasons for stalls or low occupancy and options.
Explore the performance of your application per selected GPU metrics over time.
Analyze the hottest SYCL* standards or OpenCL™ kernels for inefficient kernel code algorithms or incorrect work item configuration.

Configure Characterization Analysis

Use the Characterization configuration option to:

Monitor the Render and GPGPU engine usage (Intel Graphics only)
Identify which parts of the engine are loaded
Correlate GPU and CPU data

When you select the Characterization radio button, the configuration section expands with additional options:

Overview metric set includes additional metrics that track general GPU memory accesses such as Memory Read/Write Bandwidth, GPU L3 Misses, Sampler Busy, Sampler Is Bottleneck, and GPU Memory Texture Read Bandwidth. These metrics can be useful for both graphics and compute-intensive applications.
Compute Basic (with global/local memory accesses) metric group includes additional metrics that distinguish accessing different types of data on a GPU: Untyped Memory Read/Write Bandwidth, Typed Memory Read/Write Transactions, SLM Read/Write Bandwidth, Render/GPGPU Command Streamer Loaded, and GPU EU Array Usage. These metrics are useful for compute-intensive workloads on the GPU.
Compute Extended metric group includes additional metrics targeted only for GPU analysis on the Intel processor code name Broadwell and higher. For other systems, this preset is not available.
Full Compute metric group is a combination of the Overview and Compute Basic event sets.
Dynamic Instruction Count metric group counts the execution frequency of specific classes of instructions. With this metric group, you also get an insight into the efficiency of SIMD utilization by each kernel.

The Characterization drop-down menu provides platform-specific presets of the GPU metrics. All presets, except for the Dynamic Instruction Count, collect data about execution units (EUs) activity: EU Array Active, EU Array Stalled, EU Array Idle, Computing Threads Started, and Core Frequency; and each one introduces additional metrics:

NOTE:

You can run the GPU Compute/Media Hotspots analysis in Characterization mode for Windows*, Linux* and Android* targets. However, you must have root/administrative privileges to run the analysis in this mode.

For the Characterization analysis, you can also collect additional data:

Use the Trace GPU programming APIs option to analyze SYCL, OpenCL™, or Intel Media SDK programs running on Intel Processor Graphics. This option may affect the performance of your application on the CPU side.

For SYCL or OpenCL applications, you may identify the hottest kernels and identify the GPU architecture block where a performance issue for a particular kernel was detected.

For Intel Media SDK programs, you may explore the Intel Media SDK tasks execution on the timeline and correlate this data with the GPU usage at each moment of time.

Support limitations:
- OpenCL kernels analysis is possible for Windows and Linux targets running on Intel Graphics.
- Intel Media SDK program analysis is possible for Windows and Linux targets running on Intel Graphics.
- Only Launch Application or Attach to Process target types are supported.
NOTE:

In the Attach to Process mode if you attached to a process when the computing queue is already created, VTune Profiler will not display data for the OpenCL kernels in this queue.
Use the Analyze memory bandwidth option to collect the data required to compute memory bandwidth. This type of analysis requires Intel sampling drivers to be installed.
Use the GPU sampling internal, ms field to specify an interval (in milliseconds) between GPU samples for GPU hardware metrics collection. By default, the VTune Profiler uses 1ms interval.

Configure Source Analysis

In the Source Analysis, VTune Profiler helps you identify performance-critical basic blocks, issues caused by memory accesses in the GPU kernels.

Basic Blocks Latency option helps you identify issues caused by algorithm inefficiencies. In this mode, VTune Profiler measures the execution time of all basic blocks. Basic block is a straight-line code sequence that has a single entry point at the beginning of the sequence and a single exit point at the end of this sequence. During post-processing, VTune Profiler calculates the execution time for each instruction in the basic block. So, this mode helps understand which operations are more expensive.
Memory Latency option helps identify latency issues caused by memory accesses. In this mode, VTune Profiler profiles memory read/synchronization instructions to estimate their impact on the kernel execution time. Consider using this option, if you ran the GPU Compute/Media Hotspots analysis in the Characterization mode, identified that the GPU kernel is throughput or memory-bound, and want to explore which memory read/synchronization instructions from the same basic block take more time.

In the Basic Block Latency or Memory Latency profiling modes, the GPU Compute/Media Hotspots analysis uses these metrics:

Estimated GPU Cycles: The average number of cycles spent by the GPU executing the profiled instructions.
Average Latency: The average latency of the memory read and synchronization instructions, in cycles.
GPU Instructions Executed per Instance: The average number of GPU instructions executed per one kernel instance.
GPU Instructions Executed per Thread: The average number of GPU instructions executed by one thread per one kernel instance.

If you enable the Instruction count profiling mode, VTune Profiler shows a breakdown of instructions executed by the kernel in the following groups:

Control Flow group	`if, else, endif, while, break, cont, call, calla, ret, goto, jmpi, brd, brc, join, halt` and `mov, add` instructions that explicitly change the ip register.
Send & Wait group	`send, sends, sendc, sendsc, wait`
Int16 & HP Float \| Int32 & SP Float \| Int64 & DP Float groups	Bit operations (only for integer types): `and, or, xor,` and others. Arithmetic operations: `mul, sub,` and others; `avg, frc, mac, mach, mad, madm`. Vector arithmetic operations: `line, dp2, dp4,` and others. Extended math operations.
Other group	Contains all other operations including `nop`.

In the Instruction count mode, VTune Profiler also provides Operations per second metrics calculated as a weighted sum of the following executed instructions:

Bit operations (only for integer types):
- and, not, or, xor, asr, shr, shl, bfrev, bfe, bfi1, bfi2, ror, rol - weight 1
Arithmetic operations:
- add, addc, cmp, cmpn, mul, rndu, rndd, rnde, rndz, sub - weight 1
- avg, frc, mac, mach, mad, madm - weight 2
Vector arithmetic operations:
- line - weight 2
- dp2, sad2 - weight 3
- lrp, pln, sada2 - weight 4
- dp3 - weight 5
- dph - weight 6
- dp4 - weight 7
- dp4a - weight 8
Extended math operations:
- math.inv, math.log, math.exp, math.sqrt, math.rsq, math.sin, math.cos (weight 4)
- math.fdiv, math.pow (weight 8)

NOTE:

The type of an operation is determined by the type of a destination operand.

vtune -collect gpu-hotspots [-knob <knobName=knobValue>] -- <target> [target_options]

Knobs: gpu-sampling-interval, profiling-mode, characterization-mode, code-level-analysis, collect-programming-api, computing-task-of-interest, target-gpu.

NOTE:

For the most current information on available knobs (configuration options) for the GPU Compute/Media Hotspots analysis, enter:

vtune -help collect gpu-hotspots

Example

This example runs the gpu-hotspots analysis in the default characterization mode with the default overview GPU hardware metric preset:

vtune -collect gpu-hotspots -knob enable-gpu-runtimes=true -- /home/test/myApplication

What's Next

When the data collection is complete, do one of the following to view the result:

Use the -report action to view the data from command line.
Use the -report-output action to write report to a .txt or .csv file
Open the data collection result (*.vtune) in the VTune Profiler graphical interface.

Parent topic: Run Command Line Analysis

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gpu-hotspots Command Line Analysis

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