C3 state is unstable with my OC settings, work around? (i7 4770K)

[Zoeff]

I've currently got my i7 4770K OC'd to 4.5Ghz at 1.27v. Any lower voltage is unstable, so is any higher clockspeed at any voltage. Not what I was hoping for but I'll deal with it. However I'd like to at least take advantage of Haswell's (new?) power saving features but I can't even enable the C3 state without getting a BSOD with a random STOP code every 30 minutes. Right now it's running at 1.27v all the time...

I tried increasing the voltage of both the vCore and vRing but that didn't help. Does anybody know of a way to get the C3 state to work without decreasing the clockspeed?

Thanks.

 

[blackened23]

I think I know the answer to this. To my understanding, the iVR in the Haswell chip is (obviously) always enabled but will use adaptive voltage at all times if you enable C3/C6 in your BIOS. So what this means, is that if you're doing any type of stress testing with C3 enabled - AVX workloads can cause the adaptive voltage to go higher than desirable. IIRC AVX instructions add +.1V to the voltage used.

Is there any particular reason to enable C3? I usually just use C1 with C3 and C6 disabled. From what i've read most overclockers turn C3 and C6 off while overclocking Haswell, from what I remember.

This is just my rough understanding, if i'm wrong someone please correct me. I do recall reading from various other boards that C3/C6 will always enable adaptive voltage, although this isn't something that I have direct experience with.

 

[Zoeff]

I think I know the answer to this. To my understanding, the iVR in the Haswell chip is (obviously) always enabled but will use adaptive voltage at all times if you enable C3/C6 in your BIOS. So what this means, is that if you're doing any type of stress testing with C3 enabled - AVX workloads can cause the adaptive voltage to go higher than desirable. IIRC AVX instructions add +.1V to the voltage used.

Is there any particular reason to enable C3? I usually just use C1 with C3 and C6 disabled. From what i've read most overclockers turn C3 and C6 off while overclocking Haswell, from what I remember.

AIDA64 shows the idle power consumption of the CPU package when idling as ~30watts when C3 is off and about ~9w when it's on. In CPU-Z the vCore drops to as low as 0.13v but sticks at 1.27v when C3 is off. That said, I don't know if these numbers are accurate though...

I'm also somewhat worried about the longevity of the chip with it being on 1.27v all the time although from what I can gather it isn't that high of a voltage but it's a concern nonetheless.

 

[coffeejunkee]

I think I know the answer to this. To my understanding, the iVR in the Haswell chip is (obviously) always enabled but will use adaptive voltage at all times if you enable C3/C6 in your BIOS. So what this means, is that if you're doing any type of stress testing with C3 enabled - AVX workloads can cause the adaptive voltage to go higher than desirable. IIRC AVX instructions add +.1V to the voltage used.

I don't think that has anything to do with it. I have IVB and beyond a certain frequency C3/C6 states just cause instability no matter what (and it was the same with my previous i5 750). Only workarounds are dropping the frequency or disabling C3/C6. And yes, the power savings are pretty big.

 

[blackened23]

I don't think that has anything to do with it. I have IVB and beyond a certain frequency C3/C6 states just cause instability no matter what (and it was the same with my previous i5 750). Only workarounds are dropping the frequency or disabling C3/C6. And yes, the power savings are pretty big.

Not true, I mentioned this because Haswell differs from IVB due to the iVR. When you enable C3 or C6, adaptive voltage is automatically enabled since it is on-die. Overclocking characteristics differ slightly due to the iVR. This is all mentioned in the Gigabyte Z87 overclocking guide, by the way (with regards to C3 and C6). Again, C3/C6 interacts with Haswell differently than with IVB. Also, AVX instructions with adaptive voltage enabled causes the cpu to "over-conpensate" with regards to voltage, so this has created situations where prime95 applies too much voltage during 100% load - and that doesn't necessarily happen during normal use. So this all ties in to why disabling C3/C6 is usually preferred when overclocking..

Gigabyte Z87 oc guide here: http://www.overclock.net/t/1401976/the-gigabyte-z87-haswell-overclocking-oc-guide

 

[coffeejunkee]

Well, I read that already and I skimmed it again, but the only thing I can find is:

"However now that Haswell has a built in VRM there is almost little reason to use offset mode b/c if you enable C3 power state and EIST the CPU multiplier and voltage drop together even if you have set a manual voltage without offset."

Which is actually nothing new and also has nothing to do with the IVR, since this is the same behaviour that all cpu's with c-state technology display. Lets not make it more complicated than it is, and just accept c-states will at some point cause instability.