Overclocking Broadwell

For any user that has overclocked an Intel processor since Sandy Bridge, there is not much new to see here. Overclocking, for those unfamiliar with the term, means adjusting the settings of the system to make a component run faster, typically outside its specifications and at the expense of power but with the benefit of a faster system.

There's is a large community around overclocking, with motherboard manufacturers giving special options to make overclocking easier, as well as bigger and better CPU coolers to move the extra heat generated away from the processor faster to keep it cool. Some users use liquid cooling, either prebuilt arrangements or custom designs, on either the processor or the graphics card or both. One original purpose to overclocking was to end up buying a cheap component and ending with performance similar to an expensive component. Since 2011, Intel now restricts overclocking to a few high end models, meaning that the goal is to make the fastest, faster.

Asking a processor to run faster than its specifications requires more power. This is usually provided in terms of voltage. This increases the power into the system and raises energy lost as heat in the system, which has to be removed, and power consumption goes up (usually efficiency also goes down). Financial services and high frequency trading is an example of an industry that relies on ultimate fast response times regardless of efficiency, so overclocking is par for the course to get better results and make the trade faster than the next guy. Typically we are then left with individuals who need to process work quicker, or gamers looking for a better frame rate or the ability to increase settings without losing immersion. There is a separate group of individuals called extreme overclockers that are not concerned with everyday performance and insist on pushing the hardware to the limit by using coolants such as liquid nitrogen to remove the extra heat (350W+) away. These individuals are on the precipice of stability, only needing to be stable enough to run a benchmark and compare scores around the word. The best extreme overclockers are picked up by PC component manufacturers to help build future products (eg HiCookie and Sofos at GIGABYTE, NickShih at ASRock, Coolice and Shamino at ASUS) or at retailers to build a brand (8Pack at OverclockersUK).


Extreme overclocking at MSI’s HQ

Here at AnandTech, we mainly focus on 24/7 stability (although I have roots in the extreme overclocking community) as our diverse readership ranges from the non-clockers to enthusiasts. This means a good high end air cooler or a liquid cooler, namely in this case either the Cooler Master Nepton 140XL liquid cooler in a push/pull configuration with the supplied fans or a 2kg TRUE Copper air cooler with a 150CFM Delta fan. Both of these are more than sufficient to push the hardware for general overclocking and 24/7 use (though I hesitate to recommend the TRUE Copper for a regular system due to its mass unless upright).


The Cooler Master Nepton 140XL

In our testing, we keep it relatively simple. The frequency of a modern Intel processor is determined by the base frequency (~100 MHz) and the multiplier (20-45+). These two numbers are multiplied together to give the final frequency, and our overclocking is performed by raising the multiplier.

The other variable in overclocking is the voltage. All processors have an operating voltage out of the box, known as the VID or stock voltage. In general, the processor architecture will have a stock voltage within a certain range, and processors with that architecture will fall on the spectrum. As time goes on, we might find that the average VID falls on new processors within the same architecture due to improvements in the manufacturing process, but it ultimately is the luck of the draw. When a faster frequency is requested, this draws more power and in order to remain stable, the voltage should be increased. Most motherboards have an auto calibration tool for voltage based on the set frequency, though these tend to be very conservative values to ensure all processors are capable. Users can adjust the voltage with an offset (e.g. +0.100 volts) or in most cases can set the absolute voltage (as in 1.200 volts). For a given frequency, there will be a minimum voltage to which the processor is stable, and the process by-and-large is a case of trial and error. When the system works, the frequency/voltage combination is typically tested for stability using stress tests to ensure proper operation, as well as probing temperatures of the system to avoid overheating which causes the processor to override the settings and induce a low voltage/frequency mode to cool down.

There is a tertiary concern in that when a processor is performing work, the voltage across the processor will drop. This can result in instability, and there are two ways to approach this - a higher initial voltage, or adjusting what is called the load line calibration which will react to this drop. Both methods have their downsides, such as power consumption or temperatures, but where possible most users should adjust the load line calibration. This ensures a constant voltage no matter the processor workload.

At AnandTech, our overclocking regime is thus - we test the system at default settings and acquire the stock voltage for the stock frequency. Then we set the processor multiplier at one higher than normal, and set the voltage to the round down to the 0.1 volt level (e.g. 1.227 VID becomes 1.200). The system is then tested for stability, which our case is a simple stability test consisting of the POV-Ray benchmark, five minutes on the OCCT stress test and a run of 3DMark Firestrike. If this test regime is successful, and the CPU remains below 95C throughout without overheating, we mark it as a success and raise the multiplier by one. If any test fails (either the system does not boot, the system gets stuck or we get a blue screen), we raise the voltage by 0.025 volts and repeat the process at the same multiplier. All the adjustments are made in the BIOS and we get an overall picture of how the processor performance and temperature scales with voltage.

Here are our results with the Broadwell i7-5775C in the MSI Z97A Gaming 6 :

Our top result was 4.2 GHz on all cores, reaching 80C. When we selected 4.3 GHz, even with another 0.300 volts, the system would not be stable.

To a number of people, this is very disappointing. Previous Intel architectures have over clocked from 4.4 GHz to 5.0 GHz, so any increase in base performance for Broadwell is overshadowed by the higher frequency possible on older platforms. This has been a recent unfortunate trend in the overclocking performance of Intel’s high end processors since Sandy Bridge:

Intel 24/7 Overclocking Expected Results in MHz
  Stock Speed Good OC Great OC
Sandy Bridge i7 3400 4700 4900
Ivy Bridge i7 3500 4500 4700
Haswell i7 3500 4300 4500
Broadwell i7 3300 4100 4300

Not mentioned in the table, but for Haswell a Devil's Canyon based processor (such as the i7-4790K) could yield an extra +100-200 MHz in temperature limited situations as we found during our testing.

It is worth noting at least two points here. When Intel reduces the process node size, the elements of the processor are smaller and removing the heat generated is more problematic. Some of this can be mitigated through the fundamental design of the processor, such as not having heat generating logic next to each other and then used in the program in quick succession to make a hotspot. However, if a processor is fundamentally designed as a mobile first platform, overclocking may not even be a consideration at the design phase and merely tacked on as a ‘feature’ to certain models at the end.

Other methods have been used in the past to increase overclockability, such as changing the thermal interface material between the processor and the heatspreader. Intel did this on its Devil’s Canyon line of processors as a ‘Haswell upgrade’ and most results showed that it afforded another 10ºC of headroom. To that extent, many users interested in getting the most out of their Haswell processors found the best ways to remove a heatspreader (voiding the warranty) but getting better overclocking performance.

With all that said, it is important to consider what we are dealing here with Broadwell. This is a Crystal Well design, which looks like this:

This is an image taken for us when we reviewed the i7-4950HQ, the first Crystal Well based processor aimed specifically for high powered laptops and all-in-one devices. On the left is the processor die, and on the right is the eDRAM die, both on the same package. The thing to note here is that when the heatspreader is applied, different parts of the package will generate different amount of heat. As a result, this needs to be planned in accordance with the design.

What I’m specifically getting to here is thermal paste application. Many users here will have different comments about the best way to apply thermal paste, and for those following the industry they will remember how suggested methods change over time based on the silicon in the package. For the most part, the suggested methods revolve around a pea-sized blob in the center of the processor and a heatsink with sufficient force to help spread the paste. This minimizes air bubbles which can cause worse performance.

As a personal side note, I heavily discourage the credit card/spreading method due to the air bubble situation. The only arrangement where the spreading application is used should be for sub-zero overclocking.

With Broadwell, I took the pea-sized blob approach, strapped on a big cooler, and went to work. Almost immediately the processor temperature under load rose to 90ºC, which seemed extremely high. I turned the system off, removed the cooler, and placed it back on without doing anything, and the temperature under load dropped a few degrees. After some trial and error, the best anecdotal temperature arrangement was for a line of thermal paste from top to bottom of the CPU (where the arrow on the corner of the CPU is in the bottom left).

Put bluntly, the reason why this method works better than the pea is down to where the heat generating spots on the CPU are. With a pea sized blob in the middle, with a slightly wrong mounting, it will spread to the eDRAM rather than over the processor. A line ensures that both are covered, transferring heat to the cooler.

Now I should note that this method is useful when you are in a temperature limited overclock situation. It would seem that our CPU merely would not go above 4.2 GHz, regardless of the voltage applied. But in terms of thermal management, thermal paste application became important again.

The Intel Broadwell Review Part 2 Comparing IPC: Memory Latency and CPU Benchmarks
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  • Shadow7037932 - Monday, August 3, 2015 - link

    Still running a i7 920 @ 3.8Ghz on custom water cooling. OS, SSDs, HDDs, GPUs, have all been upgraded since 2009. Still holding it's own in gaming and multithreaded software (video rendering).

    Also, with the hexacore X5650 being available for around $70-100 used, I can probably breathe a bit more life into this.
    Reply
  • milli - Tuesday, August 4, 2015 - link

    I invested big time in my X58 platform but it's still going strong. One year ago I upgraded my i7 920 to a Xeon X5650 (which I bought second hand for like $100). Now I have a six core HT 32nm OC'd beast that runs much cooler than my 920. I can't believe this platform is now 7 years old. Reply
  • Jetpil0t - Thursday, August 6, 2015 - link

    I have been waiting for so long to upgrade my 2500k an R9 290, was looking at a 6600k and Fury X but for like $2,000 the performance really isn't there. Second hand 290 for $250 will probably be my next upgrade and still faster than a brand new 6600k Fury build. More money for games I guess. Reply
  • michael2k - Monday, August 3, 2015 - link

    Is that entirely true? It seems from the graphs that you can expect 10% to 20% improvement in performance at the same clock compared to Sandy Bridge and the Broadwell is a good 30% less in terms of power consumption. In other words the 0.25V difference in overclock is exactly the reason Broadwell consumes 30% less power. Since you don't care about the power then you can clock it up and volt it up and see a 10% to 20% improvement in performance. You can argue that the 10% to 20% improvement isn't worth it, of course. The IPC gains only matter if you care to overclock the Broadwell part. Reply
  • sonny73n - Tuesday, August 4, 2015 - link

    "my ivy bridge 3570k does the same clock with 1.075v."

    1.075v @4.2GHz? Are you sure you didn't mistype? Prime95 stress test?
    Reply
  • Jetpil0t - Thursday, August 6, 2015 - link

    Still rocking a i5 2500k @ 4.0Ghz and an R9 290 @ 1.1Ghz and it's rockin along no problem, I want to but new shiny things, but there is zero reason to, which is nice for the value but a little odd given the age of this processor. If I had known I was going to be hanging onto this CPU for so long I would have picked up the i7 2600/2700k, but even then, the i5 2500k is a powerhouse, apparently. Just puts into perspective how crazy powerful these CPUs were 5 years ago when they landed. Reply
  • Jetpil0t - Thursday, August 6, 2015 - link

    They should just take each of these CPUs to 4.0Ghz locked and bench it out, I bet the 2600k still fires up there with the best of them. The sample used here is still stock, so with an OC it's more or less up there all the way through to a 980ti. Reply
  • Oxford Guy - Thursday, January 21, 2016 - link

    Proper Broadwell overclocking appears to require that the EDRAM clock be changed. They didn't do that here, hence the poor result. Reply
  • K_Space - Monday, August 3, 2015 - link

    For desktop users the article only consolidated what was already known: hold tight to your Haswell CPU until Skylake (and even then you probably won't need to upgrade). The Z97 chipset is such a mature platform and the high frequency clocked parts have dropped in price. The 4790K is an absolute brute. Haswell -just like Sandy and Nehalem is going to be very stretchy generation. Reply
  • Nagorak - Tuesday, August 4, 2015 - link

    Forget that, just hold tight to your Sandy Bridge. Four years running and you can make up most of the difference in IPC by just cranking up the clock. Once you take the lower frequency into account, Broadwell's ~18% improvement drops to only around 10%. Reply

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