NVME power-save tuning

[baybal]

Is your feature request related to a problem? Please describe.

NVME SSDs have a number of power save options other than ASPM, namely:

• Lowest power management level settings
• Host memory non-operational access
• Autonomous power state transition
• Interrupt coalescing
• Volatile write cache

Describe the solution you'd like

A clear and concise description of:

• Autonomous power state transition and the lowermost power state setting is almost always a good choice to enable
• Other controller dependent operations can be considered after getting a better idea of how safe, and how common is their support

Additional context

Add any other context and references about the feature request here:

• NVME-CLI should be able to set all of these features with any relatively new kernel (5.4+)

[linrunner]

Interesting. I wasn't aware yet.

Autonomous power state transition and the lowermost power state setting is almost always a good choice to enable

I would appreciate some more input on your part:

• How does one parameterize nvme-cli for APST?
• What values do you suggest for the AC and the BAT profile?
• Can you say how much savings (in mW) this will bring on your hardware, e.g. in idle and with a defined IO load?

NVME-CLI should be able to set all of these features with any relatively new kernel (5.4+)

I've become reluctant to integrate additional external tools. Last but not least, it hinders package upgrades for some distributions when new dependencies are added. So: Is there also a possibility to enable the features via sysfs?