Bug#1078005: Enable Intel Idle

[Andrew Jorgensen <ajorgens@google.com>]

Hi Salvatore,

One of my colleagues supplied this explanation:

""'
intel_idle is a kernel module that implements specialized logic for
handling CPU idle/sleep states. This logic is optimized for Intel CPUs
to achieve better results than what is possible through the ACPI
C-state mechanism. For example, intel_idle can specify C-state target
residency different than 2*latency. Better results here means lower
wakeup latency (vs ACPI) while not compromising performance and power
savings. Without intel_idle, many VMs will use HLT for putting the CPU
cores to sleep, which will only put Intel CPUs in a shallow sleep
state, thus wasting power that could otherwise be saved or used by
other cores by boosting higher.

Importantly, intel_idle requires the presence of MWAIT instruction.
For some time, this hasn't been available in virtualized environments,
but it is now relatively widespread:
- GCE: https://cloud.google.com/compute/docs/cpu-platforms#frequency_behavior
- AWS: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/processor_state_control.html

Note this module is already present and used in many other cloud
distro images: Ubuntu, CentOS, RHEL, Rocky, CentOS to name a few.
"""

So in summary, the benefits to the Debian cloud kernel user are lower
wakeup latency and the ability to boost other cores higher by putting
some cores into a deeper sleep state (making power and thermal budget
available to adjacent cores).

Kind regards,
Andrew Jorgensen