Any word on RT 8.1 finally offering Tegra 3 5th Battery-Saving Core support?

[Bacalaohombre]

It's been like this for a year. The RT tablets are still underclocked to save power from the lack of the 5th power saving core that all Android devices running on a Tegra 3 have. It even says on the Nvidia site that it's still under development, but they may have just stopped caring, since the Surface 2 is soon coming out with the Snapdragon 800.

It would really be great to finally get support for this.

 

[berty6294]

It's been like this over a year. The RT tablets are still underclocked to save power from the lack of the 5th power saving core that all Android devices running on a Tegra 3 have. It even still says on the Nvidia site that it's still under development, but they may have just stopped caring, since the Surface 2 is soon coming out with the Snapdragon 800.

incorrect, using Tegra 4 not Snapdragon 800.

 

[Bacalaohombre]

incorrect, using Tegra 4 not Snapdragon 800.

What source? I read that it's using the Snapdragon.

 

[berty6294]

What source? I read that it's using the Snapdragon.

I don't feel like finding the source, but it was part of leaked information and the CEO of Nvidia also confirmed working with Microsoft on the next Surface!


will they open up the 5th core? I doubt it, but its a possibility with 8.1. I couldn't tell you for sure.

 

[mrpuny]

I've wondered about this myself, and even posted a similar question here some time ago. I've started to suspect the issue may be with Windows itself rather than nVidia slacking off.

If you read nVidia's doc on the Variable SMP architecture (http://www.nvidia.com/content/PDF/tegra_white_papers/tegra-whitepaper-0911b.pdf) the way it's supposed to work is that as CPU load decreases, the system will park cores until it's only running on a single regular core. If the load drops low enough, that single core gets switched to the battery saver core.

On my Surface RT with both Windows 8 and the 8.1 preview, leaving the resource monitor running, I've never seen less than two cores active. Up to two cores get parked, but never three. So not only is the 5th battery saver core not supported, but apparently neither is running on a single regular core. This brought back a memory. Windows NT had (has?) distinctly different HALs for single and multiprocessor systems. There are support articles like this one (Use Device Manager to Switch from Uniprocessor to Multiprocessor Support) that talked about using Device Manager to update the HAL if adding a second processor to a single processor system. There are also some discussions like this one where potential performance issues are mentioned if running a multiprocessor HAL on a uniprocessor system (ACPI Multiprocessor Hal on Uniprocessor Machine). Now these are somewhat old, and don't directly apply to this situation with the Tegra, but given that Windows RT currently never seems to use less than 2 cores, I wonder if there's some architectural issue in Windows NT that prevents it from being able to dynamically switch between single and multicore operation. It wouldn't surprise me since prior to the Tegra, it was probably never a design goal.

 

[Bacalaohombre]

damn, then why does nvidia tease us with that "[SUP]**[/SUP] Windows RT support still under development"! i wish i never read it.

 

[mrpuny]

damn, then why does nvidia tease us with that "[SUP]**[/SUP] Windows RT support still under development"! i wish i never read it.

Well, it's just a guess on my part, and I may be completely wrong. But even if I'm right, it may still be in development, just that Microsoft is doing the development (or MS and NVidia together). And if low level changes to Windows are necessary, I could see them taking a while to implement since they would probably have to test the changes on against all systems based on the NT kernel from phone to server, and I guess now Xbox One as well, assuming they're trying to keep a common code base. I'm still hopeful it'll show up in the final release of 8.1, but we'll find out soon enough,

 

[inteller]

I've wondered about this myself, and even posted a similar question here some time ago. I've started to suspect the issue may be with Windows itself rather than nVidia slacking off.

If you read nVidia's doc on the Variable SMP architecture (https://forums.windowscentral.com/e...s%2Ftegra-whitepaper-0911b.pdf&token=dSBp3ngI) the way it's supposed to work is that as CPU load decreases, the system will park cores until it's only running on a single regular core. If the load drops low enough, that single core gets switched to the battery saver core.

On my Surface RT with both Windows 8 and the 8.1 preview, leaving the resource monitor running, I've never seen less than two cores active. Up to two cores get parked, but never three. So not only is the 5th battery saver core not supported, but apparently neither is running on a single regular core. This brought back a memory. Windows NT had (has?) distinctly different HALs for single and multiprocessor systems. There are support articles like this one (Use Device Manager to Switch from Uniprocessor to Multiprocessor Support) that talked about using Device Manager to update the HAL if adding a second processor to a single processor system. There are also some discussions like this one where potential performance issues are mentioned if running a multiprocessor HAL on a uniprocessor system (ACPI Multiprocessor Hal on Uniprocessor Machine). Now these are somewhat old, and don't directly apply to this situation with the Tegra, but given that Windows RT currently never seems to use less than 2 cores, I wonder if there's some architectural issue in Windows NT that prevents it from being able to dynamically switch between single and multicore operation. It wouldn't surprise me since prior to the Tegra, it was probably never a design goal.

except that it isn't handled like that. if you go down to one CPU you don't require a uniprocessor HAL....Windows RT has a distinct Connected Standby mode (soon to be renamed something else in 8.1) in that mode the main cores should be turned off and all of that low CPU activity like checking email and such would be handled by the 5th core.

 

[mrpuny]

except that it isn't handled like that. if you go down to one CPU you don't require a uniprocessor HAL....Windows RT has a distinct Connected Standby mode (soon to be renamed something else in 8.1) in that mode the main cores should be turned off and all of that low CPU activity like checking email and such would be handled by the 5th core.

You're right, you can run a single core with a multiprocessor HAL, but the one link above had a comment from a poster that there were potential performance issues. More importantly, though, I've never seen anything about being dynamically able to switch between single and multicore operation. All the discussions online relate to changes (adding/removing physical CPUs or their virtualized equivalents) while the system is shut down. It's not something that happened while Windows is running. As I wrote, there's some ability in Windows 8 to dynamically shut off cores, because with resource monitor open, I can see two cores getting parked. But it never appears to drop down to a running on a single main core even when the CPU load is essentially nothing.

As for connected standby, I don't see how that really applies. I mean, yes, if the 5th core was active, then all the things going on while in that mode should be able to occur on the battery saver core, which would potentially improve the standby time over what the Surface RT can currently achieve. However, in the scenarios presented in NVidia's whitepaper, the 5th core has potential applications during regular operation such as audio/video playback. This quote, for example from pp. 6-7.

"The Companion core is used primarily when the mobile device is in active standby and performing background tasks such as Email syncs, Twitter updates, Facebook updates etc. It is
also used for applications that do not require significant CPU processing power, such as streaming audio, offline audio, and both online or offline video playback. Note that both audio and video playback, in addition to video encoding, are largely processed by hardware-based encoders and decoders. "

 

[inteller]

It would be much easier to implement the battery saver core in connected standby than try to manage it with the current parking scheme in awake mode. The battery savings we'd see in connected standby would be immense to offset not having it in active mode

 

[mrpuny]

OK, I officially declare that I have no idea what I'm talking about. Thought to check a couple of Windows 8 desktops I have around. One 4 core, the other a 2 core machine. Both will intermittently park all but one core when there's not much going on (CPU load hovering around 10-20% or so). So those ramp down to running on one core with no problem and that shows up within seconds of watching the resource monitor. But I've gone back to the Surface RT and watched until the screen times out, and it never, ever appears to park more than two of the four cores even when the CPU usage is like 2-5%. I wonder why RT seems less aggressive about parking cores than my desktops.

 

[DenniSundaY]

Yeah noticed that too. You can watch it all day long,but only the 3th and 4th core are ''parked way'' and the second core won't park at all. I think it even doesn't park in standby. Really a shame because the battery life could (easily) be improved. I hope the 5th core is going to be unlocked short after the windows 8.1 update. But they haven't talked about it in the surface 2, which also has a tegra cpu with 5th core. Is the batterylife improved by adding more mAh, because of the tegra 4 cip which could use less power (and still run 1,7 GHz) or do they finally have unlocked the 5th core?

 

[inteller]

you read the description on nvidias site and it says the 5th core is invisible to the OS and applications so this must be something really low level Nvidia needs to enable.

 

[DenniSundaY]

Still no love after 8.1 update

 

[inteller]

I think it is too complicated to come in a general OS release. It will come out of band I'm guessing, if it comes at all. It is critical they do something though

 

[DenniSundaY]

I don't think it is coming. Tegra 4 isn't using it either in the Surface 2 I thought. But if they are unlocking it at all, they will update both devices. Tegra 4 is just a tegra 3 with more gpu cores and higher clock speed so...