CPU PLL an Odd Beast

paulselhi

paulselhi

paulselhi

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3 Sep 2009
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125
I have been trying for ages to fine tune my 4.2 Ghz I7 930 overclock on a gigabyte x58a-ud3r rev 1 board with f5 BIOS 12 GB Corsair 1600 RAM

I may have a naff chip but i cannot get it stable under 1.392 V showing in cpu-z, I have tried with and without LLC but it seems 1.392 v is the cut off point.

Temps are acceptable at max 85 C with an Noctua D14 in Prime and rarely hit a max of 83 when rendering 3d stuff, but it is a bit high for my liking

I have been toying with voltages to see what i can get away with and it seems that on i have to set qpi-vtt to 1.355 and all other voltages on auto to see what the MB does with them. The only change it makes is to push the IOH core to 1.16

Now here is the odd part, i decided on a whim to lower my CPU PLL, drastically, in fact it is at 1.30 ( default 1.80) and i seem to have no adverse effects at all, prime stable

Does anyone know what is the deal with cpu pll as most say to raise it for stability and does anyone have any suggestions of how i can manipulate other settings to allow for a lower vcore ( 1.44375 in BIOS with LLC Level 1 gives me 1.392 under load)
 
gigabyte mobo's tend to like a reduction in pll voltage, asus boards go the other way.

i've got mine down 1 notch to 1.7v for pll and it's stable at 4.2 atm with 1.36Vcore and 1.33v qpi. level 1 pll as well :)

as for lowering other voltages, well, if your chip doesn't like running lower it probably won't shift down too much... could always try level 2 llc?
 
Level 1 or 2 does not make that much difference since either has to be manipulated to get that magic 1.392 cpuv under load.

I am experimenting with raising QPI-VTT to see if that allows lower CPU V but i some how doubt it

4.2 Ghz is a good o/c with 12 GB RAM it is the high volts and temps that worry me. If the volts are acceptable and it is the temps i should worry about i suppose i could water cool but for the additional £200 + for a water cool which may just get me to 4.3 Ghz i would be better off buying a 6 core and running that at 4.0 Ghz which would easily out perform an overclock of 4.3 on a quad
 
tbh dude you're probably better off just dropping it to 4GHz and lower voltages - there's bugger all difference in 200/300MHz really...
 
4.2ghz stable with all six slots occupied would be an exceptionally good overclock. Based on your opening post I think you're using a fairly lax definition of stability though.

QPI over 1.35V (ish) is considered high. Most +4ghz overclocks with 6 sticks of ram feature qpi on the bad side of 1.4V. If you're stable, at 4.2ghz, with 1.45Vcore and 1.35V qpi thank your lucky stars and don't push it any further.
 
not sure what you mean by a lax definition of stability, 12 hours prime stable sounds stable to me and temps though hot do not exceed 85 C (case temp 27-28 room temp av 26)

Yes 4.0 Ghz is the sweet spot and though i tell myself again and again that that is what i will live with something keeps dragging me back to that 4.2 number, is this Arthur Dent syndrome ?
 
Each to their own. I spent a long time troubleshooting 4.2 ghz w/ 12gb that passed 24hrs of prime 95 and 30 loops of ibt without any fuss, but froze whenever I moved a lot of data into/out of ram in a short space of time. It's given me quite a cynical attitude to "prime stable".

I quite like 200x20 with ram at 1200c6. Doesn't stop me periodically trying to get 4.5ghz stable though :)

I posted quite a lot of results in this thread, might be worth a look.
 
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