i7: Any advantage to matching core and uncore clock?

[MechGeek]

Hi everybody, my first post here so go easy on me.

I was an avid overclocker back in the 300A and Tbird days, but multicore has added a whole new twist for me. I settled on the overclock in the sig after finding that the machine wasn't stable at 3.8GHz at safe temperatures if LinX and Prime95 were run simultaneously. (BSODs, calculation errors, silent data corruption)

Anyway... Setting the QPI link speed in my BIOS has no effect for some reason; it runs an "Auto" scale from 3.2-4.0(!) before switching multipliers. So I'm stuck running 3.6GHz uncore @ 1.45V at my Bclk. But I wonder, since my CPUs are also clocked at 3.6GHz, is there any performance advantage with synchronous operation of the cores and cache/QPI?

[cky2k6]

i'm not sure i'm getting you, thats your qpi speed, your uncore is a different frequency. you want to run the uncore at a lower frequency than qpi but at least twice your ram speed. So, your uncore at this clock should be 3.2ghz.

[swale]

Yep just confirming the above correct info you need a QPI at least twice as fast as your RAM speed

[cky2k6]

Yep just confirming the above correct info you need a QPI at least twice as fast as your RAM speed

thats not exactly what i said... uncore has to be twice ram speed, not qpi. qpi has to be faster than uncore by a 9:8 ratio.

[Xello]

you want to run the uncore at a lower frequency than qpi

qpi has to be faster than uncore by a 9:8 ratio.

Not at all, higher the uncore the better and it's powered by memory voltage

Boost those bandwidths

[MechGeek]

Ahhh OK I didn't realize the uncore and QPI ran on separate clocks. And that clears up the 9:8 ratio thing I've heard about.

So I'd need to crank QPI to 4050MHz to match the clocks uncore=core=3.6GHz. uncore must be >= 2*dram, not == 2*dram? Any advantage to matching clocks, besides the extra bandwidth?

[Xello]

Ahhh OK I didn't realize the uncore and QPI ran on separate clocks. And that clears up the 9:8 ratio thing I've heard about.

So I'd need to crank QPI to 4050MHz to match the clocks uncore=core=3.6GHz. uncore must be >= 2*dram, not == 2*dram? Any advantage to matching clocks, besides the extra bandwidth?

Yeah they are seperate clocks, they should be shown seperately in your bios.

QPI is the point-to-point technology that connects your cpu to your memory, northbridge, and southbridge. Uncore is the part of the cpu that has the L3 cache and memory controller.

So, increasing uncore multi will up the clock and boost L3 cache bandwidth, as well as memory bandwidth. Uncore is fed by dram voltage.

You will likely not be able to run QPI @ 4050mhz as it's hard to get it stable past 4ghz. I'd set your QPI to 18x. There's not much to gain by upping QPI clock higher than this.

uncore must be >= 2*dram, not == 2*dram?

Uncore multi must be at least 2x dram, that's all.

Matching clocks doesn't matter, they don't sync up and give extra bandwidth or anything like that as a result.

I've been very brief, you should check out Saaya's 101 thread and keep it handy as a reference

http://www.xtremesystems.org/forums/...d.php?t=205688

[MechGeek]

Thanks for the link Xello. Bookmarked. And I retract my question.