P55 Chipset Overclocking: PCIe Intervals for Stability?

[Bleser]

Hello all,

So I have a brand new Core i5 750 and Asus P55 motherboard on the way and I've been reading as many reviews/guides as I can about overclocking this new setup.

One thing that keeps lurking/popping up is something that hasn't really been an issue since the Pentium II/III/IV days: the PCI bus being locked to the base/bus clock. Basically, from what I understand, you have to increase the base clock in 33 MHz increments in order to not overclock your actual PCIe component bus (video card, etc). Doing so usually affects overall stability more than the fact that the CPU is overclocked.

From Anand's article:

"Unfortunately the PCIe controller on Lynnfield is tied to the BCLK. Increase the BCLK to overclock your CPU and you're also increasing the PCIe controller frequency. This doesn't play well with most PCIe cards, so the first rule of thumb is to try and stay at 133MHz multiples when increasing your BCLK."

Can anyone confirm or deny this? Does it basically come down to the BIOS on the motherboard you're using? If it is true then I'm only going to be happy with 133/166/200 base clocks and nothing in-between... and 166 would be a clock Anand was not able to achieve with turbo on, so I doubt I will be able to, which is dissapointing.

Thoughts?

 

[Bleser]

 

[Bleser]

Dumb question: are CPU multipliers unlocked on the Core i5/i7 series? I see the adjustment option in the BIOs manual... I've been out of the overclocking game for a while... but is this really the case?

If so, then 166x19 would be the sweet spot with turbo mode enabled... ~3.2 GHz base, ~4 GHz in turbo for single-threaded apps... is this correct?

 

[cusideabelincoln]

They aren't unlocked in a sense you can't raise them higher (you have to let Turbo Mode raise them). You can, I believe, lower the multis from stock settings.

 

[Bleser]

Originally posted by: cusideabelincoln
They aren't unlocked in a sense you can't raise them higher (you have to let Turbo Mode raise them). You can, I believe, lower the multis from stock settings.

That would be perfect if that were true. That way I can run on 133/166/200 bus speeds and not overclock the PCIe bus beyond spec and still overclock the processor. This, I believe, is really only an issue on the new i5/i7 processors with the integrated PCIe controllers... yet no one has really confirmed my initial thought/question.

 

[cusideabelincoln]

Yeh I'm surprised no one has came in here with more info on that. I can't comment because I don't own the chipset, and I haven't really read many overclocking reviews of it.

 

[Mod7PCs]

Hmmm...... Interesting question here. I will put this on my list of things to do with the 750 I have.

From the overclocking I have done I have not experienced any stability issues at say a 165 bus which would be the absolute extreme you could over clock the PCIe from what info you guys are giving me.

Thinking about it though.....I just changed out coolers to a smaller one (unfortunately the side panel didn't fit with the other). Short story I also left the SLI bridge off (accidentally). Well with the new fan my OC failed......wondering if it has to do with the PCIe and not being in SLI.

Time to test that theory. Sorry so long winded here just kind of typing what I was thinking.

Okay back to what I was doing and here a link to the i5 overclocking thread we have been bantering on.

i5 Overclock

 

[Bleser]

Originally posted by: Mod7PCs
Hmmm...... Interesting question here. I will put this on my list of things to do with the 750 I have.

From the overclocking I have done I have not experienced any stability issues at say a 165 bus which would be the absolute extreme you could over clock the PCIe from what info you guys are giving me.

Thinking about it though.....I just changed out coolers to a smaller one (unfortunately the side panel didn't fit with the other). Short story I also left the SLI bridge off (accidentally). Well with the new fan my OC failed......wondering if it has to do with the PCIe and not being in SLI.

Time to test that theory. Sorry so long winded here just kind of typing what I was thinking.

Okay back to what I was doing and here a link to the i5 overclocking thread we have been bantering on.

i5 Overclock

I'm not certain it's an issue, and I'm not even sure I have my math right. It may be one of those things where your cards can either handle it or they can't, and if they can, then it doesn't matter and you're not hurting anything. Or it could be that they'll only last six or nine months at that 165 bus... I have no idea. Need some clarification!

If Anand's statement is right, and it has to be 133 multiples (not 33 as I have it above), then you'd have to run a 266 bus to get it back to spec. If you set teh multiplier at 10x, then you'd have 2.66 GHz non-turbo, but ~4GHz when turbo'd... I think......

 

[faxon]

My question is, can you change the multipler on the PCIe bus clock indipendently of the CPU. If so you could use lower PCIe multi and use a lower CPU multi to sync bus speeds

 

[Bleser]

Originally posted by: faxon
My question is, can you change the multipler on the PCIe bus clock indipendently of the CPU. If so you could use lower PCIe multi and use a lower CPU multi to sync bus speeds

See the quote at the beginning of this thread:

From Anand's article:

"Unfortunately the PCIe controller on Lynnfield is tied to the BCLK. Increase the BCLK to overclock your CPU and you're also increasing the PCIe controller frequency. This doesn't play well with most PCIe cards, so the first rule of thumb is to try and stay at 133MHz multiples when increasing your BCLK."

So, in a word, no, you have no control over the multiplier according to this statement.

 

[Mod7PCs]

Originally posted by: Bleser
If Anand's statement is right, and it has to be 133 multiples (not 33 as I have it above), then you'd have to run a 266 bus to get it back to spec. If you set teh multiplier at 10x, then you'd have 2.66 GHz non-turbo, but ~4GHz when turbo'd... I think......

This presents an interesting position here. For those that have the notion that a larger buss and smaller multiplier are better.....with turbo enabled it very well could be. Just something to think about something I will be doing

Cheers