Underclock Atom and disable cache?

[sefsefsefsef]

Does anyone know of a platform I could buy that would allow me to underclock an Atom CPU and disable its L2 cache? I need something like this for a school project. It doesn't need to be the latest Atom, but I would like to be able to do some tests in the 200 MHz range, if that's possible.

Does anyone have any experience with this, or know of a motherboard that allows underclocking or disabling cache?

 

[NTMBK]

This should do the trick...

Joking aside, I don't know of a platform that would let you do that. Sounds like an interesting project though, what're you doing?

 

[Exophase]

What motherboard are you using? The BIOS options may have something that lets you adjust CPU speed.

I remember the old Mendocino Celerons had a BIOS option that let you disable L2 cache. But I haven't seen that anywhere since. It could be because the L2 was still not yet fully integrated into the die back then.

 

[pantsaregood]

Best thing you can do is check BIOS options of various Atom motherboards. I've seen recent AMD boards that support disabling cache, so it isn't unthinkable to disable the cache of an Atom.

 

[sefsefsefsef]

I haven't purchased anything yet, and looking through the manual PDFs of a few different motherboards hasn't given me any hope of finding underclocking or cache disabling controls.

I need this for a study I'm doing about the performance of certain applications on very low power, low performance CPU cores. I'd prefer to use x86 just for simplicity in getting the workloads to run, but ARM may be an option if anyone knows of any good ARM boards that come with a couple gigabytes of RAM.

 

[Exophase]

Best thing you can do is check BIOS options of various Atom motherboards. I've seen recent AMD boards that support disabling cache, so it isn't unthinkable to disable the cache of an Atom.

The glaring question is if the CPU can even run without L2 cache in the first place. An option to disable L3 in an AMD CPU makes sense - they make chips on the same uarch with no L3. But you'll never see that option on Core-i series processors because the L3 cache is required for the design to work.

Don't know what the case is for Atom but I'd be pretty surprised if you find such an option anywhere. You benefit more from tightly coupling cache if it never makes sense to remove it, and the L2 cache block may (and probably does) content vital parts of the external memory interface and coherency communications.

 

[Exophase]

I haven't purchased anything yet, and looking through the manual PDFs of a few different motherboards hasn't given me any hope of finding underclocking or cache disabling controls.

I need this for a study I'm doing about the performance of certain applications on very low power, low performance CPU cores. I'd prefer to use x86 just for simplicity in getting the workloads to run, but ARM may be an option if anyone knows of any good ARM boards that come with a couple gigabytes of RAM.

You can find a few ARM boards with 2GB of RAM. This one is particularly cheap:

http://www.hardkernel.com/renewal_2011/products/prdt_info.php?g_code=G135341370451

I don't think I understand why your task is leading you to want to disable L2 cache on an Atom. It's not as if Atoms don't use L2 in phones. Maybe you could tell us more about your goals here?

 

[Mr. Pedantic]

I don't know if it's possible to disable L2 cache from the motherboard. Even if you could, wouldn't that slow it down massively? L1 is pretty small and Atom doesn't have an L3.

 

[Exophase]

I don't know if it's possible to disable L2 cache from the motherboard. Even if you could, wouldn't that slow it down massively? L1 is pretty small and Atom doesn't have an L3.

It'd slow it down a lot, but not nearly as much at 200MHz as it would at 1.6GHz (assuming memory clocks stay the same)

 

[sefsefsefsef]

It'd slow it down a lot, but not nearly as much at 200MHz as it would at 1.6GHz (assuming memory clocks stay the same)

The whole point of underclocking and disabling the cache is that I want it to go slower.

 

[Exophase]

The whole point of underclocking and disabling the cache is that I want it to go slower.

Okay, but why exactly? Are you being vague on purpose because you can't talk about your study or do you merely not want to talk about it?

You said it was to evaluate low power devices. An Atom at 200MHz with its L2 disabled (in theory) is not a good simulation for anything whatsoever. L2 cache is every bit as much, if not more, of a power consumption optimization as it is a performance optimization.

Furthermore, I'm going to assume there's a reason you need all that memory for running stuff. But that too sounds like you're creating a scenario that doesn't match anything in the real world. You want a device that's so low power that you want a 200MHz Atom w/o L2 to try capture its performance, but you're okay with having it paired with RAM that takes at least hundreds of mW.

 

[sefsefsefsef]

Okay, but why exactly? Are you being vague on purpose because you can't talk about your study or do you merely not want to talk about it?

You said it was to evaluate low power devices. An Atom at 200MHz with its L2 disabled (in theory) is not a good simulation for anything whatsoever. L2 cache is every bit as much, if not more, of a power consumption optimization as it is a performance optimization.

Furthermore, I'm going to assume there's a reason you need all that memory for running stuff. But that too sounds like you're creating a scenario that doesn't match anything in the real world. You want a device that's so low power that you want a 200MHz Atom w/o L2 to try capture its performance, but you're okay with having it paired with RAM that takes at least hundreds of mW.

All of your assumptions are correct. I cannot discuss exactly what I'm going to do with it, but I do need to know if such a product is available. Thanks, guys.