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vmm: Add support for enabling AMX in vm guests

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AMX is an x86 extension adding hardware units for matrix
operations (int and float dot products). The goal of the extension is
to provide performance enhancements for these common operations.

On Linux, AMX requires requesting the permission from the kernel prior
to use. Guests wanting to make use of the feature need to have the
request made prior to starting the vm.

This change then adds the first --cpus features option amx that when
passed will enable AMX usage for guests (needs a 5.17+ kernel) or
exits with failure.

The activation is done in the CpuManager of the VMM thread as it
allows migration and snapshot/restore to work fairly painlessly for
AMX enabled workloads.

Signed-off-by: William Douglas <william.douglas@intel.com>
This commit is contained in:
William Douglas
2022-03-01 10:25:30 -08:00
committed by William Douglas
parent 96e2bedc10
commit 6b0df31e5d
9 changed files with 111 additions and 6 deletions
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24
docs/cpu.md
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@@ -17,11 +17,12 @@ struct CpusConfig {
kvm_hyperv: bool,
max_phys_bits: u8,
affinity: Option<Vec<CpuAffinity>>,
features: CpuFeatures,
}
```
```
--cpus boot=<boot_vcpus>,max=<max_vcpus>,topology=<threads_per_core>:<cores_per_die>:<dies_per_package>:<packages>,kvm_hyperv=on|off,max_phys_bits=<maximum_number_of_physical_bits>,affinity=<list_of_vcpus_with_their_associated_cpuset>
--cpus boot=<boot_vcpus>,max=<max_vcpus>,topology=<threads_per_core>:<cores_per_die>:<dies_per_package>:<packages>,kvm_hyperv=on|off,max_phys_bits=<maximum_number_of_physical_bits>,affinity=<list_of_vcpus_with_their_associated_cpuset>,features=<list_of_features_to_enable>
```
### `boot`
@@ -187,3 +188,24 @@ _Example_
In this example, assuming the host has 4 CPUs, vCPU 0 will run exclusively on
host CPUs 2 and 3, while vCPU 1 will run exclusively on host CPUs 0 and 1.
Because nothing is defined for vCPU 2, it can run on any of the 4 host CPUs.
### `features`
Set of CPU features to enable.
This option allows the user to enable a set of CPU features that are disabled
by default otherwise.
The currently available feature set is: `amx`.
The `amx` feature will enable the x86 extension adding hardware units for
matrix operations (int and float dot products). The goal of the extension is to
provide performance enhancements for these common operations.
_Example_
```
--cpus features=amx
```
In this example the amx CPU feature will be enabled for the VMM.