Developer Guide

  • 2021.2
  • 06/11/2021
  • Public
Contents

Select a Cache Partitioning Preset

Intel recommends those experimenting with software SRAM or cache partitioning to start by using the presets included in the cache configurator tool. Presets are designed to cover the majority of use cases and will overwrite any existing cache partitioning configuration on the system. You can also use the cache configurator to further refine the configuration as needed.
In general, the presets partition the cache to:
  • Establish isolated cache regions dedicated to real-time applications, also known as
    workloads
  • Restrict the GPU from accessing the entire L3 cache, and avoid overlap with cache partitions dedicated to real-time workloads
  • Dedicate a small portion of the cache for low-latency I/O operations
  • Configure L2 and L3 software SRAM buffers
The cache configurator follows certain rules regarding the placement of software SRAM buffers in cache and how the remaining cache is partitioned after accounting for software SRAM buffers. For details, see Recommended Approach and Effects.
If you have completed the steps in the Get Started Guide, you applied a preset that has dedicated cache for two real-time workloads and enough software SRAM to run the cache allocation sample. Since the preset contains a valid software SRAM region, it overwrote the default software SRAM region provided as part of the BIOS setting. Once a cache partitioning scheme has been applied (either from a preset or custom partitioning scheme), if the partition scheme included any dedicated cache regions for real-time workloads, the system administrator needs to set the appropriate Class of Service on the core running the real-time workload. For details, see Assign Classes of Service to Cores.
If you want to partition the cache on your own without referencing any of the provided presets, Intel recommends reserving software SRAM (see Reserve Software SRAM) before partitioning the remaining cache resources.

Steps

The existing cache configuration and software SRAM buffers will be overwritten by the selected preset.
To select a preset:
  1. Confirm system settings based on the preset that you will choose:
    • If you intend to choose a preset that has software SRAM: On the target system, confirm that the
      Software SRAM
      option in system firmware is enabled. For details, see Software SRAM Setting.
    • If you intend to choose a preset that does not have software SRAM: On the target system, confirm that the
      Software SRAM
      option in system firmware is disabled. For details, see Software SRAM Setting.
  2. If you have not done so, launch the tool as described in Launch the Cache Configurator.
  3. At tool launch, select
    P
    :
    Would you like to add (A) or delete (D) a cache allocation? Or would you like to change the way the configuration is partitioned? (P) P
  4. At the prompt, select one of the presets. For details, see Preset Summary. If you want to exit this screen without selecting any preset, press
    U
    .
  5. The selected preset will overwrite the current configuration. All changes before this will be overwritten. After selecting a preset, enter
    Y
    to apply the configuration and go to the reboot screen. You can check the resulting configuration. If it suits you, enter
    Y
    . You can continue configuration editing by entering
    C
    . To cancel applying the preset, enter
    U
    .
  6. Presets include dedicated cache for real-time workloads. After applying the new partitioning scheme and rebooting into it, you will need to take additional steps outside the cache configurator to allow your real-time application to use the dedicated cache. For details, see Assign Classes of Service to Cores.
  7. After use, enable RTCM to allow the cache allocation library to work properly. You can enable RTCM with the following commands:
    For systems running the PR1 release of the Yocto Project*-based BSP for Intel Atom® x6000E Series processors, run:
    /usr/share/tcc_tools/scripts/setup_ssram_v1/control_rtcm.sh enable reboot
    For other systems, run:
    /usr/share/tcc_tools/scripts/setup_ssram/control_rtcm.sh enable reboot
  8. If the preset has dedicated cache for I/O operations, confirm that
    WRC Feature
    is enabled in BIOS.
    Intel® TCC Mode
    enables the setting by default. If the setting is disabled, you may see reduced performance.

Product and Performance Information

1

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