Intel® VTune™ Profiler User Guide

User Guide

Contents

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 DPC++ 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:
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 DPC++, 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 DPC++ 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.
    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)
The type of an operation is determined by the type of a destination operand.

Syntax

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

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.