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doc: update rdt config tutorial

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Add some clarification and updates for 3.1

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>
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David B. Kinder 2022-08-08 12:44:35 -07:00 committed by David Kinder
parent 785ce3346c
commit cb91722dd5
1 changed files with 36 additions and 38 deletions
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doc/tutorials/rdt_configuration.rst
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@ -7,59 +7,57 @@ About Intel Resource Director Technology (RDT)
********************************************** **********************************************
On x86 platforms that support Intel Resource Director Technology (RDT) On x86 platforms that support Intel Resource Director Technology (RDT)
allocation features, the ACRN hypervisor can partition the shared cache among allocation features, the ACRN hypervisor can help minimize cache misses by
VMs to minimize performance impacts on higher-priority VMs, such as real-time partitioning the shared cache among VMs. “Shared cache” refers to cache that is
VMs (RTVMs). “Shared cache” refers to cache that is shared among multiple CPU shared among multiple CPU cores. By default, VMs running on these cores are
cores. By default, VMs running on these cores are configured to use the entire configured to use the entire cache, effectively sharing the cache among all VMs
cache, effectively sharing the cache among all VMs without any partitions. This and without any partitioning. This design choice may cause too many cache misses
design may cause too many cache misses for applications running in for applications running in higher-priority VMs, such as real-time VMs (RTVM),
higher-priority VMs, negatively affecting their performance. The ACRN hypervisor negatively affecting their performance. The ACRN hypervisor can help minimize
can help minimize cache misses by isolating a portion of the shared cache for cache misses and improve performance by isolating a portion of the shared cache
a specific VM. for a specific VM.
ACRN supports the following features: ACRN supports the following features:
* Cache Allocation Technology (CAT) Cache Allocation Technology (CAT)
* Code and Data Prioritization (CDP) The CAT support in the hypervisor isolates a portion of the cache for a VM from
* Virtual Cache Allocation Technology (vCAT) other VMs. Generally, certain cache resources are allocated for the RTVMs to
reduce performance interference by other VMs attempting to use the same cache.
The CAT support in the hypervisor isolates a portion of the cache for a VM from
other VMs. Generally, certain cache resources are allocated for the RTVMs to
reduce performance interference by other VMs attempting to use the same cache.
The CDP feature in RDT is an extension of CAT that enables separate control over Code and Data Prioritization (CDP)
code and data placement in the cache. The CDP support in the hypervisor isolates The CDP feature in RDT is an extension of CAT that enables separate control over
a portion of the cache for code and another portion for data for the same VM. code and data placement in the cache. The CDP support in the hypervisor isolates
a portion of the cache for code and another portion for data for the same VM.
ACRN also supports the virtualization of CAT, referred to as vCAT. With
vCAT enabled, the hypervisor presents CAT to a selected set of VMs to allow the Virtual Cache Allocation Technology (vCAT)
guest OSes to further isolate the cache used by higher-priority processes in ACRN also supports virtualizing CAT, referred to as vCAT. With
those VMs. vCAT enabled, the hypervisor presents CAT to a selected set of VMs, allowing the
guest OSs to further isolate the cache used by higher-priority processes in
those VMs.
Dependencies and Constraints Dependencies and Constraints
***************************** *****************************
Consider the following dependencies and constraints: Consider the following dependencies and constraints:
* The hardware must support RDT in order for ACRN to enable RDT support in the * The hardware must support RDT for ACRN to enable RDT support in the
hypervisor. hypervisor.
* The cache must be shared cache (cache shared across multiple CPU cores), as * The cache must be shared cache (cache shared across multiple CPU cores) and
opposed to private cache (cache that is owned by only one CPU core). If the not private cache (cache that is owned by only one CPU core). If the
cache is private, CAT, CDP, and vCAT have no benefit because the cache is cache is private, CAT, CDP, and vCAT have no benefit because the cache is
already exclusively used by one core. For this reason, the ACRN Configurator already exclusively used by one core. For this reason, the ACRN Configurator
will not allow you to configure private cache. will not allow you to configure private cache.
* The ACRN Configurator relies on the board configuration file to provide CAT * The ACRN Configurator displays CAT configuration parameters based on data
information that it can use to display configuration parameters. On Tiger Lake reported in the board configuration file. Some Intel platforms are known to
systems, L3 CAT, also known as LLC CAT, is model specific and have L3 CAT even though it's not reported via the architectural CPUID
non-architectural. For these reasons, the Board Inspector doesn't detect LLC interface. In this situation, the board inspector detects availability of L3
CAT, and therefore doesn't provide LLC CAT information in the board CAT by trying to access the CAT MSRs directly. Versions of the board inspector
configuration file even if the board has LLC CAT capabilities. The Board before v3.1 only used the CPUID interface and would indicate L3 CAT wasn't
Inspector offers a way to manually add LLC CAT information to the board supported in this circumstance.
configuration file via a command-line option described in
:ref:`board_inspector_tool`. Run the Board Inspector with the command-line
option, then import the board configuration file into the ACRN Configurator.
* The guest OS in a VM with vCAT enabled requires utilities in that OS for * The guest OS in a VM with vCAT enabled requires utilities in that OS for
further cache allocation configurations. An example is the `resctrl further cache allocation configurations. An example is the `resctrl
@ -159,7 +157,7 @@ The table title shows important information:
The above example shows an L2 cache table. VMs assigned to any CPU cores 2-6 can The above example shows an L2 cache table. VMs assigned to any CPU cores 2-6 can
have cache allocated to them. have cache allocated to them.
The table's y-axis shows the names of all VMs that are assigned to the CPU cores The table's columns show the names of all VMs that are assigned to the CPU cores
noted in the table title, as well as their vCPU IDs. The table categorizes the noted in the table title, as well as their vCPU IDs. The table categorizes the
vCPUs as either standard or real-time. The real-time vCPUs are those that are vCPUs as either standard or real-time. The real-time vCPUs are those that are
set as real-time in the VM's parameters. All other vCPUs are considered set as real-time in the VM's parameters. All other vCPUs are considered
@ -170,7 +168,7 @@ standard vCPUs (VM0 vCPU 2 and 6).
The Service VM is automatically assigned to all CPUs, so it appears in the standard category in all cache tables. The Service VM is automatically assigned to all CPUs, so it appears in the standard category in all cache tables.
The table's x-axis shows the number of available cache chunks. You can see the The table's rows show the number of available cache chunks. You can see the
size of each cache chunk in the note below the table. In the above example, 20 size of each cache chunk in the note below the table. In the above example, 20
cache chunks are available to allocate to the VMs, and each cache chunk is 64KB. cache chunks are available to allocate to the VMs, and each cache chunk is 64KB.
All cache chunks are yellow, which means all of them are allocated to all VMs. All cache chunks are yellow, which means all of them are allocated to all VMs.