Stability Impact of Cache Frequency

[Leegit]

In the BIOS for my mobo, I have cache frequency set to auto which basically makes cache freq = clock freq when less than 4GHz and cache freq = 4GHz when above 4GHz. Is there any significant impact on stability when say OCin to 4.5GHz+ if the cache freq is still tied to 4GHz. I'm beginning to suspect there is but would like to know what others have found?

 

[Kenrou]

I have no issues with stability until i hit 4.7, but need to add +0.01v for anything over 4.5, YMMV ofc.

 

[Leegit]

What is your cache frequency set at when you OC to 4.7GHz+?

 

[EarthDog]

I think he's saying that is his cache frequency...

I personally don't touch it. Typically there are no tangible gains, so, I leave it on auto. I am perfectly stable that way on 6700k at 4.7-4.9ghz for cpu speed.

 

[Johan45]

I typically run my cache 1-200MHz behind the core speed but that's for benching. The cache is fast enough at 4.0 for just about everyone in daily tasks.

 

[Kenrou]

What is your cache frequency set at when you OC to 4.7GHz+?

Below 4.7ghz match with CPU frequency, above lock it at 4.7.

I think he's saying that is his cache frequency...

I personally don't touch it. Typically there are no tangible gains, so, I leave it on auto. I am perfectly stable that way on 6700k at 4.7-4.9ghz for cpu speed.

Only reason i don't leave it on auto is because at 4.8ghz+ every now and then Windows boots with it matched with CPU and then and causes instability (my 4.8ghz/4.9ghz really doesn't like cache above 4.7), if at stock lock it at 4.1 default.

 

[Tír na nÓg]

Talking Haswell-E, and not Skylake, so not sure if it is relevant or not...

I run the cache between 4.2 and 4.3 24/7.

Even for benching ([email protected] to 5GHz), I did not notice any significant difference between cache [email protected] and above (up to 4.45). Maybe the higher cache speed is beneficial for high freq/low latency DDR4, but up to 3350/CL14 (where is my wall), it seems going above 4GHz has very little effect if any.

 

[Kenrou]

It has a small beneficial effect in memory intensive programs and like what, 1 fps at 4.7+ ? doesn't really matter but then again it doesn't hurt as well unless you have a high overclock, and most skylake stay at 4.6ghz/4.8ghz. I think of it as a little bit more "free" performance

 

[EarthDog]

I don't have time to tinker with stuff like that for negligible gains on my daily driver. Benching...different story.

 

[Johan45]

One important difference between haswell and skylake is the way the power is delivered. Haswell has a seperate voltage for cache where skylake is tied directly to the CPU core voltage. Stabilizing cache at higher frequencies will need a higher CPU voltage

 

[Leegit]

Thanks for the feedback guys.

I'll probably end up driving my CPU around 4.5 - 4.7 from the results I'm seeing now. Wasn't sure if cache freq was limiting this in some way as I've never messed with it. Need to get my thermals under control at 4.7GHz and re-stress it

 

[Woomack]

Cache frequency affects max memory bandwidth. However if you are not benching then leave it at auto or set something like 4.2GHz. I set 4.2GHz CPU+cache for all my memory tests. For these clocks it doesn't need much more than stock voltage on most 6600/6700K.

 

[Dolk]

I agree with Woomack, unless you are benching or doing some heavy memory operations with an OCed system (above 4.0GHz in this case) than you would be required to turn this setting off, and stabilize the system.

I didn't realize this was an option for Intel CPUs and its very interesting that you can change this setting.

The small increase in performance is due to the cache buffer to send to memory not being filled due to the offset in frequencies. With the frequencies matched, the buffer is less filled and throughput increases.

 

[Woomack]

On Intel maximum memory bandwidth is actually limited by cache speed. On X99 you can see it more clearly. Without cache overclocking there is no point to buy high frequency memory.
After OC you can see up to 30% memory bandwidth gain. Still not many applications can use it. On skylake it's not affecting memory speed so much and on haswell-e there is already high base bandwidth and what it needs is faster access time.