Bug#1078005: Enable Intel Idle

[Salvatore Bonaccorso <carnil@debian.org>]

Control: tags -1 - moreinfo

Hi Andrew,

On Fri, Jan 10, 2025 at 09:00:50AM -0800, Andrew Jorgensen wrote:
> 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).

Many thanks for providing the more info. We are going to enable
intel_idle for the cloud kernel then.

Regards,
Salvatore