User Guide

Contents

Throttling Analysis (Preview)

Use throttling analysis to identify performance issues that result from the CPU operating at temperatures above thermal and power limits.
This is a PREVIEW FEATURE on Windows* OS and Linux* OS. A preview feature may or may not appear in a future production release. It is available for your use in the hopes that you will provide feedback on its usefulness and help determine its future. Data collected with a preview feature is not guaranteed to be backward compatible with future releases. Please send your feedback to parallel.studio.support@intel.com or to intelsystemstudio@intel.com.

What is throttling?

When you observe an unexpected drop in system performance or a degradation when the system is not overloaded, your system may be displaying throttling behavior. Throttling describes a drop in operating frequency as the system responds to a breach of safe operating power and temperature limits to prevent a catastrophic event like a thermally induced shutdown.
For example, if the operating temperature of the CPU exceeds the thermal limits specified, the frequency drops from the peak value to a lower level in order to allow the system to cool down. Once this has happened, the CPU needs to ramp up its frequency to the peak value sustained previously. This phase is the throttling phase where the CPU slows down initially and ramps up eventually.
The drop in frequency to restore safe CPU operating temperature can result in significant performance loss.

How can you prevent your system from throttling?

Unfortunately, throttling is an unavoidable occurrence. The performance of a CPU is ultimately governed by power consumption which is turn determined by how quickly a system can cool down. Since the thermal algorithms of an OS govern the violation of thermal limits, you cannot alter your application to prevent the system from throttling.
However, you can take steps to reduce the extent of throttling observed:
  • Run a throttling analysis using
    Intel® VTune™
    Profiler
    . Use the information to determine necessary optimizations to the cooling system. Ultimately, throttling is a hardware issue.
  • If you are running a lot of Intel® Advanced Vector Extensions (Intel® AVX) instructions, convert your code to run on a regular CPU instead.

When should you run throttling analysis?

Throttling is a performance issue that is caused by power supplied to the system. Run throttling analysis when you observe a slowdown in performance in one of these situations:
  • After using vector instructions.
  • After substantially loading up the system.
  • When you expect a performance boost but observe a degradation instead.

Run throttling analysis

Prerequisite:
To use the throttling analysis type, you must run
Intel® VTune™
Profiler
as an administrator.
  1. On the Welcome screen, click
    Configure Analysis
    .
  2. In the
    HOW
    pane, go to the
    Platform Analysis
    group and select
    Throttling
    analysis type.
  3. In the
    WHAT
    pane, make sure you have selected an application in the
    Launch application
    section.
  4. Click
    Start
    to run the analysis.
When the analysis completes, check the Summary window to see if throttling was observed. Under each type of throttling, you can see the number of instances for each profiled entity.
See the
Correlated Metrics
tab for a graphical representation of this information. In this example, running the system power at peak performance has caused CPU frequency to exceed maximum turbo frequency.
Correlated Metrics from Throttling Analysis
For a more detailed analysis, see individual tabs for each type of throttling and understand the reasons that caused each instance.
In the throttling count table, you can see all of the sources for throttling that are covered by the analysis.
The
Reason
column indicates the number of sampling points where throttling occurred, as well as the reason causing it.
The
Not Reason
column displays the count of sample points where throttling did not occur.
CPU Throttling Reasons

Descriptions of Throttling Reasons

These tables describe the various reasons that cause CPU, GPU, and ring throttling to occur.
CPU Throttling Reasons:
In this table, Frequency refers to the processor core frequency.
Reason
Description
PROCHOT
Frequency has exceeded the OS frequency.
THERMAL
Frequency has exceeded the OS frequency due to a thermal event.
RSR-LIMIT
Frequency has exceeded the OS frequency due to a Residency State Regulation Limit violation.
RATL
Frequency has exceeded the OS frequency due to a Running Average Thermal Limit violation.
VR-THERMAL-ALERT
Frequency has exceeded the OS frequency due to a thermal alert from a processor Voltage Regulator (VR).
VR-TDC
Frequency has exceeded the OS frequency due to VR Thermal Design Current limit.
OTHER
Frequency has exceeded the OS frequency due to electrical or other constraints.
PBM-PL1
Frequency has exceeded the OS frequency due to package/platform-level power limiting PL1.
PBM-PL2
Frequency has exceeded the OS frequency due to package/platform-level power limiting PL2/PL3.
MAX-TURBO-LIMIT
Frequency has exceeded the OS frequency due to multi-core turbo limits.
TURBO-ATTENUATION
Frequency has exceeded the OS frequency due to turbo transition attenuation. This can cause performance degradation due to frequent changes in operating ratio.
GPU Throttling Reasons:
In this table, Frequency refers to the processor graphics frequency.
Reason
Description
PROCHOT
Frequency has exceeded the OS frequency.
THERMAL
Frequency has exceeded the OS frequency due to a thermal event.
RSR-LIMIT
Frequency has exceeded the OS frequency due to a Residency State Regulation Limit violation.
RATL
Frequency has exceeded the OS frequency due to a Running Average Thermal Limit violation.
VR-THERMAL-ALERT
Frequency has exceeded the OS frequency due to a thermal alert from a processor Voltage Regulator (VR).
VR-TDC
Frequency has exceeded the OS frequency due to VR Thermal Design Current limit.
OTHER
Frequency has exceeded the OS frequency due to electrical or other constraints.
PBM-PL1
Frequency has exceeded the OS frequency due to package-level power limiting PL1.
PBM-PL2
Frequency has exceeded the OS frequency due to package-level power limiting PL2/PL3.
MAX-TURBO-LIMIT
Frequency has exceeded the OS frequency due to multi-core turbo limits.
TURBO-ATTENUATION
Frequency has exceeded the OS frequency due to turbo transition attenuation. This can cause performance degradation due to frequent changes in operating ratio.
Ring Throttling Reasons:
In this table, Frequency refers to the ring interconnect in the uncore.
Reason
Description
PROCHOT
Frequency has exceeded the OS frequency.
THERMAL
Frequency has exceeded the OS frequency due to a thermal event.
RSR-LIMIT
Frequency has exceeded the OS frequency due to a Residency State Regulation Limit violation.
RATL
Frequency has exceeded the OS frequency due to a Running Average Thermal Limit violation.
VR-THERMAL-ALERT
Frequency has exceeded the OS frequency due to a thermal alert from a processor Voltage Regulator (VR).
VR-TDC
Frequency has exceeded the OS frequency due to VR Thermal Design Current limit.
OTHER
Frequency has exceeded the OS frequency due to electrical or other constraints.
PBM-PL1
Frequency has exceeded the OS frequency due to package/platform-level power limiting PL1.
PBM-PL2
Frequency has exceeded the OS frequency due to package/platform-level power limiting PL2/PL3.
MAX-TURBO-LIMIT
Frequency has exceeded the OS frequency due to multi-core turbo limits.
TURBO-ATTENUATION
Frequency has exceeded the OS frequency due to turbo transition attenuation. This can cause performance degradation due to frequent changes in operating ratio.
For more information about these reasons, see the Intel
®
64 and IA-32 Architectures Software Development Manual
.

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804