Intel® Advisor User Guide

User Guide

Contents

Investigate Memory Usage and Traffic

Accuracy Level

High

Enabled Analyses

Survey with register spill/fill analysis + Trip Counts, FLOP, Call Stacks (Characterization) + Memory Access Patterns
Collecting additional data may substantially increase report generation time. There is a variety of techniques available to minimize data collection, result size, and execution time. Check Minimize Analysis Overhead.

Result Interpretation

After you run the
Vectorization and Code Insights
 perspective with
high
 accuracy and full Characterization and Memory Access Patterns steps enabled,
Intel® Advisor
:
  • Extends the Survey report with the
    Compute Performance
     and
    Memory
     metrics.
  • Adds Memory Access Patterns data to the
    Refinement Report
     tab.

In the Survey report

Compute Performance columns in the Survey report (Vectorization perspective)
Use the FLOP data to analyze application memory usage and performance values that help you make better decisions about your vectorization strategy.
Compute Performance column
You can configure this column to show only metrics for a specific type of operations used in your application. Click the control in the
Compute Performance
 column set header and choose the desired drop-down option to:
  • Show data for floating-point operations only, for integer operations only, or for both floating-point and integer operations.
  • Determine what is counted as an integer operation in integer calculations:
    • Choose
      Show Pure Compute Integer Operations
       to count only ADD, MUL, IDIV, and SUB operations.
    • Choose
      Show All Operations Processing Integer Data
       to count ADD, ADC, SUB, MUL, IMUL, DIV, IDIV, INC/DEC, shift, and rotate operations.
Select a specific loop/function to see the details about FLOP and/or integer operation utilization in the
Code Analytics
 tab:
Details of operation utilization in the Code Analytics pane (Vectorization perspective)
Memory column
You can configure this column to show only metrics for one or more specific memory levels and specific types of operations. Click the gear icon in the
Memory
 column set header and choose the desired drop-down option to determine which columns to display in the grid:
This data is only available if cache simulation is enabled. By default,
Intel® Advisor
 collects only L1 traffic, so you will not be able to select memory levels or loads/stores.
  • Show data for
    L1
    ,
    L2
    ,
    L3
    , or
    DRAM
     memory metrics, or show a
    Customized Column Layout
    .
  • Show data for memory load operations only, store operations only, or the sum of both.
You can choose to hide the current column,
Show All Columns
, or customize the columns displayed in the grid by choosing
Configure Column Layouts
.
You can use the traffic and AI data reported in the Compute Performance and Memory columns to find the best candidates to examine the memory usage for in the Memory Access Patterns tab. For example, bad access pattern has stronger impact on loops/functions with higher AI value suggesting that you start with optimizing their memory usage.

In the Refinement report

Before running the Memory Access Patterns analysis, select loops/functions from the column in the Survey report.
Get information about types of memory access in selected loops/functions, how you traverse your data, and how it affects your vector efficiency and cache bandwidth usage by running the Memory Access Patterns analysis.
Memory access patterns affect how data is loaded into and stored from the vector registers.
Example of a Refinement report with memory access patterns (Vectorization perspective)
To analyze how the data structure layout affects performance, pay attention to the following:
  • Look for loops/functions that
    do not
     have "All Unit Strides" in the Access Pattern column to find optimization candidates.
  • Strides Distribution
     column reports the ratio of stride types for a selected loop/function and is color-coded:
    • Blue
       is unite/uniform stride, which means that the instruction access memory sequentially or within the distance of one element.
    • Yellow
       is constant stride, which means that the instructions access memory with the constant step of more than one element.
    • Red
       is irregular stride, which means that the instructions access memory addresses that change by an unpredictable number of elements from iteration to iteration.
    For vectorization,
    unit
     stride is the preferred distribution. Your goal is to eliminate irregular strides and minimize the constant stride to optimize memory usage.
  • Click a loop in the top pane to see a detailed report for this loop below in the
    Memory Access Patterns Report
     tab.
    • Review details for each stride type that contributes to the loop/function with corresponding source locations.
    • Review the size of the strides, variables accessed, and source locations and modules.
  • To optimize memory access patterns, follow the
    Intel® Advisor
    Recommendations
     for specific loops/functions.
In the
Memory Analysis Patterns Report
 tab at the bottom of the
Refinement Reports
double-click
 a line to view the selected operation's source code.
Associated
Memory Access Patterns Source
 window, from top left to bottom right:
  • View Activation
     pane -
    Enable or disable views shown in the Source view.
  • Source View
     pane -
    View source code of the selected loop/function.
  • Assembly View
     pane -
    View assembly source of the selected loop/function.
  • Details View
     pane -
    View details of the selected site.

Next Steps

Product and Performance Information

1

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