Many Power Management Updates For The Linux 4.10 Kernel

[phoronix]

Phoronix: Many Power Management Updates For The Linux 4.10 Kernel

Rafael Wysocki of Intel on Monday submitted the new ACPI and power management material for the Linux 4.10 merge window. Like most kernel cycles, there is a lot of ACPI/PM improvements on the horizon for Linux...

http://www.phoronix.com/scan.php?page=news_item&px=Linux-4.10-Power-Management

[Azrael5]

what about TSC which is the default source clock used by linux operating systems on the different machins!? When the cpus implements constant TSC (not invariant) the C1E and or EIST should be disabled!?

[davidbepo]

pstate + schedutil sounds nice

[indepe]

pstate + schedutil sounds nice

Especially if that helps schedutil to provide the same performance as "performance", when needed.

I hope the final version of this won't require another flavor of boot parameter ("intel_pstate=passive") as the experimental version apparently did, thereby making all existing options inaccessible. Who would even know about this feature?

[gilboa]

what about TSC which is the default source clock used by linux operating systems on the different machins!? When the cpus implements constant TSC (not invariant) the C1E and or EIST should be disabled!?

I'm not sure I understand your request: You want the kernel to enforce zero-PM on machines that doesn't support constant TSC?
Why? Kernel / user-land developers on such platforms should be aware of this limitation and use other clock sources instead of TSC...

- Gilboa

[indepe]

I'm not sure I understand your request: You want the kernel to enforce zero-PM on machines that doesn't support constant TSC? Why? Kernel / user-land developers on such platforms should be aware of this limitation and use other clock sources instead of TSC..

By the way, would be nice to have a portable userspace lib function around RDTSC as well, if such a thing is possible.

[indepe]

Regarding power management:

It would seem to make sense if threads were able to switch between performance / power-efficient / default modes.

In default mode, the scaling governor would determine the frequency as it does now.

In power-efficient mode, a long-running task can run at the frequency optimal for power-consumption, even if its CPU-usage will be 100%.

In performance mode, it will run at the best available frequency, even if it runs only for short time intervals and averages a low CPU-usage.

[gilboa]

By the way, would be nice to have a portable userspace lib function around RDTSC as well, if such a thing is possible.

Yeah, but nothing beats having a cross OS / platform / user-mode/kernel-mode ASM library

- Gilboa

[indepe]

Yeah, but nothing beats having a cross OS / platform / user-mode/kernel-mode ASM library

Too good to be true!

[gilboa]

Too good to be true!

Actually, I have such library for simple stuff, rdtsc, atomic counters, atomic bitmaps, etc.

- Gilboa