How to (Not) Overclock a Xeon 2660 V4

 

This summer I dumped my connection to Apple and built myself a super computer.  I’ve not regretted it for a second but due to the unique nature of my setup I’ve had quite a few questions about it.  One of the most common questions is about overclocking it and how have I tweaked my setup.

I haven’t.  That’s the short answer.  The Asus board comes with an “AI Overclock” mode with 3 levels of auto overclock specifically designed for Xeons but when I tried it when I first got the board the system wouldn’t power on so I didn’t bother again – however as the questions have carried on coming in I thought I’d give it another go.

Most Xeons are multiplier locked meaning you can’t get an easy overclock out of them by just tweaking the multiplier, voltages and cooling.  This one is an ES chip so may be unlocked but the dual motherboards don’t support this function anyway.  Furthermore, with ECC RAM and two processors to worry about overclocking a Xeon can become inherently more unreliable than just trying to overclock a single chip.  There are some low end E3 (single socket use only) that are unlocked but these are basically just i7s anyway.

With a base clock of 100Mhz I have a 2.1GHz CPU so I started tweaking 1MHz at a time.  I could get up to 103Mhz giving an overall clock speed of 2.17GHz with what seemed like a decent amount of stability.  A base clock of 104MHz did boot and gave me 2.19GHz but crashed very quickly after stress testing commenced and a 105MHz wouldn’t even get as far as the BIOS.

With the 103MHz overclock I saw my Cinebench scores go up from circa 2900 to 3150.  Whilst 70MHz might not seem a lot – with aa workload that is maximising hyperthreading that’s a theoretical 3.92GHz additional compute available to me which is a significant boost so I decided to keep the overclock.

I ran several burn-in tests and measured the thermals on the system.  I even ran Prime 95 tests for a full 24 hours without any issues reported or any change in my core temperatures (all stable under 60 degrees C).  It seemed stable enough I thought I‘d create a new post and share it… sadly that’s where things went wrong.

As soon as I started editing the video about the overclock my computer just died and started behaving badly – all the traditional signs of a poor overclock.  Since I bought this computer for stability I decided that rather than trying to overclock it that I would just roll back to my stock speeds.

Could I have got this working?  Probably.  I suspect the issue (since CPU seemed fine) was related to the RAM and turning off ECC may have helped – as might changing RAM chips I had installed.  The problem is I didn’t want to do any of that and I’m not sure that the speeds I got were worth that much effort so back to standard we go.

Can you overclock a Xeon?  Yes.  Could it be stable?  Yes.  Would I recommend it?  No.  You buy a Xeon tailored to your specification – there are so many SKUs that you can chose a clock speed versus core count tailored to your exact workload.  Along with the customisation you’ve got stability and much more reliable motherboards and RAM available to you.  Those few extra MHz are not what you’re chasing and it’s worth remembering that when you’re tempted to tinker.

Are there times I’d love more per-core power?  Absolutely – particularly during rendering which seems very bad at parallelising the workload – but this exercise has reminded me why I don’t care and I should just make a cup of tea every now and then instead of tinkering!

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