Disabling C-States

[SgtSpoon]

For anyone who is running an oc'ed i3/i5/i7 : do you have c-states disabled? Every overclocking guide mentions this as the first thing to do : disable the c-states.

I actually like the c-states. I bought the i3 530 for my new machine simply because of the impressive performance/power consumption factor. If i disable them, i hear an audible difference in the speed of my cpu-cooler (hyper 212) when idling, so its definitely running somewhat hotter.

For now, i'm running stock memory speed because the memory controller on my cpu is apparently unwilling to overclock, bclk is 166 and cpu speed is 3.5Ghz prime95-stable (testing stability of 3.66Ghz tomorrow). The goal is to see how high i get can with c-states on and all voltages to their default values.

My actual question : Why do those guides advise to disable it? Is it simply because it prevents higher overclocks (4Ghz and beyond), or is there some risk in keeping them enabled at overclocked speeds?

If it is the first, i'm going to keep it enabled, i'm not seeing much noticable real-life gains to overclocking anyway: even bad company, which has the reputation of being cpu-hungry, doesn't seem to care if it runs at 2.93Ghz or 4Ghz, while an overclock of my videocard raises average fps by 10.

 

[jthunderloc]

I've always been curious about this, currently I have an i5 750 overclocked with eist, c states, and turbo boost enabled giving me a great, dynamic overclock.

RE bad company 2, I found it doesnt care much about clock speeds, but really loves more cores.

-Wes

 

[SgtSpoon]

Nobody?

 

[biostud]

I had to disable the higher c-states to get mine stable, but I have the lower enabled.

 

[Kenmitch]

I've always been curious about this, currently I have an i5 750 overclocked with eist, c states, and turbo boost enabled giving me a great, dynamic overclock.

RE bad company 2, I found it doesnt care much about clock speeds, but really loves more cores.

-Wes

Look at it like an overclocking urban myth

It's all a matter of stability and your overclocking goal. If you can achieve both with enabled it is too your benefit. Will cut down on the heat and power requirements but it does have it's downsides also.

I'll use the i5 750 as an example as that is what I have. I have the following enabled and am 100% stable at whatever speed I decide to run at within reason. Limited by cpu vtt

Intel C1E support [enabled]
Intel Speedstep [enabled]
Turbo Mode [enabled] I need this to use the 21x multiplier
Intel C-State [Disabled] I needed to kill the 24x 1-2 core multiplier

This is the reason why the C-State is bad on the i5 750 for me at least.

If I want a max overclock of 4.2ghz then I'd have to use the following settings.

BCLK of 175 with a 1-2 core load the turbo multiplier of 24x would kick in and give me 4.2ghz. But when I had a 3-4 core load the turbo multiplier of 21x would kick in and give me 3.67ghz.

For stability reasons I had to set my voltages to get the 24x 1-2 core load stable at 4.2ghz so when the 3-4 core load multiplier kicks in and my speed drops down the voltages are way more than is required.

These are the voltages I need to run stable at 4.2ghz (Based on BCLK of 200)
vcore 1.425v
cpu vtt 1.27v (Slightly lower on 175 BCLK) My cpu likes cpu vtt based more on overall speed than the BCLK.

These are the voltages I need to run stable at 3.68ghz (Based on BCLK of 175)
vcore 1.225v
cpu vtt 1.075v

I came to the conclusion that it didn't make any sense for me to run with c-state enabled due to the excessive voltages required under 1-2 core loads. I figured that if I was gonna run with the voltages required then I might as well just have 4.2ghz on all 4 cores

Running it this way my vcore will fluctuate from 1.08v at idle to 1.425v at full load and my system will use the 9-21x multipliers and a BCLK of 200. Idles below system temp with sustained 4 core load it's in the low 60's on water.