On Wed, Feb 12, 2014 at 3:44 PM, Michael Mrozek EvilDragon@openpandora.org wrote:
Am Wed, 12 Feb 2014 15:32:20 +0200 hat Grazvydas Ignotas notasas@gmail.com geschrieben:
So if Power Management really is switched off on the OMAP5 right now and we can enable / disable cores on-the-fly, we should be pretty good here.
Well at least cpufreq is working, so I'd say it has partial powersaving.
Hmm, but it doesn't really seem to clock down when doing nothing. I'll try what it does when X is not running, just at the CPU core.
Do you know what happens when you use both cores? Do they run at the same clockspeed or can one run with 1,5GHz and the other with 0,5GHz?
According to the manual, there is only single clock generator, so both cores always run at the same clock. Some forum posters claim that Snapdragon has a feature to clock cores independently, supposedly unique feature. No idea about other SoCs..
Running PSX emulation uses 70% on one core, the other core doesn't do much (though Linux sometimes seems to move the tasks around, so the 70% are sometimes on one then on the other core).
So if both cores are clocked higher even though just one core is being used actually, that would also increas power usage.
Probably, unless the other one can go to sleep. but even if there are small tasks for the other core, it has to do them at full power.. That's why big.Little thing was developed, and OMAP lacks it. But still I think the other core should end up spending most of it's time sleeping and ignoring the fast clock, otherwise you wouldn't see power usage difference between fully loading just one core and both of them.
Additionally, the XServer is still running using fbdev only, without any hardware acceleration (which will probably lower the power usage as well).
FYI we also currently have it like that on pandora, only the video overlay is accelerated on pandora and not on OMAP5. I wouldn't put too many expectetions here..
Hmm... but even on lower resolutions moving X Windows around seems a lot slower than on the Pandora, so something is different here.
I forgot that there's NEON-optimized pixman library (which is responsible for window redrawing) on pandora, and all Debian packages are compiled without NEON because of that stupid Tegra2 SoC (Tegra2 had no NEON but was popular at it's time). So that's the disadvantage of Debian.. OTOH I don't know if those pixman optimizations were even ever merged to mainline pixman project, it might be only available as patches on Angstrom/OE only.
Maybe enabling power management is something we should look into soon, so we can do some real life tests with power management enabled.
Powersaving on OMAPs is extremely complicated, you know yourself how long it took to get it working on pandora..
Yes - is it that much different on the OMAP5 than on the OMAP3? I thought TI stuff is pretty similar, so we might be able to use it on the OMAP5 with minor changes.
Yes it's different, it needs it's own code, even though a bit of it is shared on all newer OMAPs..
Grazvydas