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Disabling a core in a 3570k?

post #1 of 18
Thread Starter 
If I want to disable a core in a 3570k that isn't going to be used in order to lower temps does it matter which core? Can I just disable the one running the hottest?
post #2 of 18
You can do what ever you want with your system of course, but i dont think you should cripple that awesome quad core. as i can see from your sig-rig you are using a liquid cooling CPU block to cool your CPU. and seems like your CPU is running at 4.5ghz, at this frequency i doubt your CPU should be running too hot that you are thinking of disabling a core or two or what ever. to answer your question, i am not sure you are able to choose which core you are able to disable, you can mess around the motherboard's bios and see what settings you can end up with.

but again i dont think you should disable anything in the first place.
post #3 of 18
if one core is running abnormally hot, disable it if you have to, but it usually won't help temps much (1-2C). Use something like CoreTemp or RealTemp and Prime95 to see if a single core is consistently hot across multiple tests, then disable it in the BIOS if you REALLY don't need it. In my Asus EFI, I can choose which core to disable, but I hear Asus has the best BIOSes, and other manufacturers may not let you choose exactly which core to turn off. It's usually not worth it, and may actually make it run hotter, as each individual core has to work harder to make up for the small tasks the last core had to do.
post #4 of 18
Quote:
Originally Posted by 267267123 View Post

if one core is running abnormally hot, disable it if you have to, but it usually won't help temps much (1-2C). Use something like CoreTemp or RealTemp and Prime95 to see if a single core is consistently hot across multiple tests, then disable it in the BIOS if you REALLY don't need it. In my Asus EFI, I can choose which core to disable, but I hear Asus has the best BIOSes, and other manufacturers may not let you choose exactly which core to turn off. It's usually not worth it, and may actually make it run hotter, as each individual core has to work harder to make up for the small tasks the last core had to do.

That is correct, + rep and welcome to OCN smile.gif
post #5 of 18
3570k on water running to hot? How fast are you trying to run it?
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post #6 of 18
Thread Starter 
I'm sorry guys I should have specified. I'm building a dedicated emulator PC and none of the emulators use more than 3 cores (most use only 2 and do some low level background processing on the 3rd). I picked up a 2700K for really cheap ($199) so I'm sticking that in my sig rig and taking the 3570K and sticking it in this emulator build. I'ts going in a Bitfenix Prodigy case with an ASRock Z77-E ITX board which has little room for aftermarket coolers if you using a PCI-E GPU. Therefore I can only fit a Noctua NH-U9B SE2 92mm heatsink on my chip and wanted to help reduced temps by disabling a 4th core that will not be used what-so-ever.
post #7 of 18
Most of the difference in temperature between cores is because Intel uses core temperature sensors that are not 100% accurate. Sensors are only accurate to +/- 5C so that much variation between cores is meaningless. It might be a "hot" core or it might just be a crappy sensor and there is no way to tell the difference.

If you want to disable a core then all you have to do is enable the core C6 sleep state in the bios and you are done. This sleep state reduces the core voltage to zero for any core that is not active.

I just did a test and went into the Asus bios, disabled 2 cores, booted up and measured power consumption of a 3570K at the wall using a Kill-a-Watt meter. I then rebooted, enabled all 4 cores and power consumption when the CPU was idle was identical. Disabling cores in the bios or in Windows by using msconfig will block access to these cores but it does not seem to accomplish anything.

Disabling a core or two will increase the load percentage on each individual core that is active which will increase the core temperature. Why would you want to do that? It makes more sense to spread the processes around to all 4 cores so none of them have to work as hard.
post #8 of 18
Quote:
Originally Posted by unclewebb View Post

Most of the difference in temperature between cores is because Intel uses core temperature sensors that are not 100% accurate. Sensors are only accurate to +/- 5C so that much variation between cores is meaningless. It might be a "hot" core or it might just be a crappy sensor and there is no way to tell the difference.
If you want to disable a core then all you have to do is enable the core C6 sleep state in the bios and you are done. This sleep state reduces the core voltage to zero for any core that is not active.
I just did a test and went into the Asus bios, disabled 2 cores, booted up and measured power consumption of a 3570K at the wall using a Kill-a-Watt meter. I then rebooted, enabled all 4 cores and power consumption when the CPU was idle was identical. Disabling cores in the bios or in Windows by using msconfig will block access to these cores but it does not seem to accomplish anything.
Disabling a core or two will increase the load percentage on each individual core that is active which will increase the core temperature. Why would you want to do that? It makes more sense to spread the processes around to all 4 cores so none of them have to work as hard.

Well, it depends on what they are running...and how they are running it. If the emulation programs are going to have core affinity set then the fourth core would truly never be used by anything but a random back ground service. Other older programs will just dump everything into one or two threads and a scheduler can not divide them up (ol' Baldur's Gate is one of my favorite examples...no matter what CPU you have it will take one thread and run it at 100% utilization. The core that gets this thread will be very hot...hotter than if I have all cores at 100% during a stress test. I've actually thought about using 8 instances of the game to be a stress test).

But yeah...that is one of the great things about multiple cores. Four cores at 30% will have a cooler overall CPU temp than two cores at 60%.

Though I think the real issue here for the OP is that I don't think you can disable one core on a Intel CPU. I've never seen a mother board that did anything but disable the CPU from a quad to a dual core...and a dual to a single core. I guess I've seen them also do quad to a single core too.
Edited by Vagrant Storm - 12/5/12 at 10:13am
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post #9 of 18
The Asus P8Z77-V board I have lets you enable 1, 2, 3 or 4 cores in the bios but in terms of idle power consumption, it doesn't make any difference so why bother. Having all four cores enabled will not hurt anything and there is nothing to be gained by disabling 1 of them so you might as well just leave them as is. Modern Intel CPUs do a great job when it comes to power management so the easiest thing to do is just let the CPU take care of itself. Using the C6 core sleep state is the easiest way to accomplish that. Idle cores can spend over 99.5% of the time with zero voltage in C6. Even if disabling cores truly worked, it is hard to improve on that.

post #10 of 18
Thread Starter 
Quote:
Originally Posted by unclewebb View Post

Most of the difference in temperature between cores is because Intel uses core temperature sensors that are not 100% accurate. Sensors are only accurate to +/- 5C so that much variation between cores is meaningless. It might be a "hot" core or it might just be a crappy sensor and there is no way to tell the difference.
If you want to disable a core then all you have to do is enable the core C6 sleep state in the bios and you are done. This sleep state reduces the core voltage to zero for any core that is not active.
I just did a test and went into the Asus bios, disabled 2 cores, booted up and measured power consumption of a 3570K at the wall using a Kill-a-Watt meter. I then rebooted, enabled all 4 cores and power consumption when the CPU was idle was identical. Disabling cores in the bios or in Windows by using msconfig will block access to these cores but it does not seem to accomplish anything.
Disabling a core or two will increase the load percentage on each individual core that is active which will increase the core temperature. Why would you want to do that? It makes more sense to spread the processes around to all 4 cores so none of them have to work as hard.

Quote:
Originally Posted by Vagrant Storm View Post

Well, it depends on what they are running...and how they are running it. If the emulation programs are going to have core affinity set then the fourth core would truly never be used by anything but a random back ground service. Other older programs will just dump everything into one or two threads and a scheduler can not divide them up (ol' Baldur's Gate is one of my favorite examples...no matter what CPU you have it will take one thread and run it at 100% utilization. The core that gets this thread will be very hot...hotter than if I have all cores at 100% during a stress test. I've actually thought about using 8 instances of the game to be a stress test).
But yeah...that is one of the great things about multiple cores. Four cores at 30% will have a cooler overall CPU temp than two cores at 60%.
Though I think the real issue here for the OP is that I don't think you can disable one core on a Intel CPU. I've never seen a mother board that did anything but disable the CPU from a quad to a dual core...and a dual to a single core. I guess I've seen them also do quad to a single core too.

Quote:
Originally Posted by unclewebb View Post

The Asus P8Z77-V board I have lets you enable 1, 2, 3 or 4 cores in the bios but in terms of idle power consumption, it doesn't make any difference so why bother. Having all four cores enabled will not hurt anything and there is nothing to be gained by disabling 1 of them so you might as well just leave them as is. Modern Intel CPUs do a great job when it comes to power management so the easiest thing to do is just let the CPU take care of itself. Using the C6 core sleep state is the easiest way to accomplish that. Idle cores can spend over 99.5% of the time with zero voltage in C6. Even if disabling cores truly worked, it is hard to improve on that.

Thank you all for providing that excellent insight. I had never even tried to disable a core or lower power consumption of the CPU before so the idea was just a theoretical one at this point. Really appreciate the info.
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