The Intel Broadwell Review Part 2: Overclocking, IPC and Generational Analysis
by Ian Cutress on August 3, 2015 8:00 AM ESTIn our first part of our Broadwell coverage, we rushed to test both the i7-5775C and the i5-5765C in our new benchmarking suite against the previous generation of Haswell processors as well as AMDs Kaveri lineup. In Part 2, we have spent more time with the architecture to see how it stacks up against the last four years of Intel, as well as probing the high end overclocking capabilities.
Since our Part 1, the news mill from Intel has been an interesting mix of reduced revenue from the PC segments but a rise in expectation as we move from a dull Q2 into an exciting Q3 with back-to-school sales on the horizon and the release of Windows 10. Throw into the mix details about Intel's delayed 10nm process node, the injection of Kaby Lake processors after Skylake to break the tick tock model and it becomes an interesting next few years for the industry.
No matter the state of the tick-tock model (or what seems to be a tick-tock-tock with Kaby Lake), Intel's goals are still the same - improve efficiency of the main processor design and boost peak performance though instruction per clock (IPC) gains with each new processor design release. Simply stating you want an improvement in IPC and actually designing the semiconductor to get a boost in performance are two opposite ends of the difficulty spectrum.
Broadwell vs. Haswell
Intel's line of Haswell (4th generation) processors were released in June 2013, with a small updated design called Haswell Refresh in mid-2014 with improved frequencies and a small a package upgrade to benefit temperatures. Haswell is the name of the architecture, updating from the architecture on Ivy Bridge but on the same 22nm process node as Ivy Bridge. An architecture update incorporates a numerical of things - either a paradigm shift in the underlying semiconductor design, or a step up from the previous orientation by aiming for the low hanging fruit (times which can be updated for the most gain and the least effort). As a result, architecture jumps usually produce big (5-25%) jumps in performance. This is a tock, to use Intel's nomenclature.
Intel's Tick-Tock Cadence | |||||
Microarchitecture | Process Node | Tick or Tock | Release Year | ||
Conroe/Merom | 65nm | Tock | 2006 | ||
Penryn | 45nm | Tick | 2007 | ||
Nehalem | 45nm | Tock | 2008 | ||
Westmere | 32nm | Tick | 2010 | ||
Sandy Bridge | 32nm | Tock | 2011 | ||
Ivy Bridge | 22nm | Tick | 2012 | ||
Haswell | 22nm | Tock | 2013 | ||
Broadwell | 14nm | Tick | 2014 | ||
Skylake | 14nm | Tock | 2015 | ||
Kaby Lake (link)? | 14nm | Tock | 2016 ? |
The other half of the equation is a tick, or the movement from a larger process node to a smaller process node. This is by and large a scaled reduction in the mask used for the processor, but there are potential benefits based on the die area of the components of the processor and the connections within. Moving down to a smaller node typically does not change the base hardware underneath, but optimizations are made based on that die area reduction. With this in mind, we typically see smaller benefits in performance (5-10%), but better improvements in power consumption due to smaller transistors needing less voltage (although this is a balance between higher leakage currents). Overall, the typical goal of a process node change is typically efficiency, making it favored in mobile platforms.
Moving from Haswell to Broadwell on the desktop is a process node change, migrating from 22nm on Haswell to 14nm on Broadwell. As a result, the first processors released under the Broadwell nomenclature were mobile focused (Core M), and the desktop end of the stack us the last one to be updated. Though the desktop side is more subtle than that - Intel has released mid-powered versions of the processor with high end integrated graphics, an approach normally reserved for mobile devices or integrated devices such as all-in-ones. Perhaps it is then unsurprising that when desktop processors are launched under the -S or -DT naming scheme, Broadwell on the desktop is part of the -H line, normally reserved for mobile processors.
We've commented on Broadwell's minor architecture adjustments over Haswell before. They focus on reducing cache misses and keeping more predicted operations in flight at any one time, reducing the need to move back out of memory and increase throughput. This is mostly achieved by exploiting the available area when function units are reduced in size from the node change - increasing the out-of-order scheduler size, increasing the L2 TLB to allow for both more local misses/larger memory jump requests, and the page miss handler doubles in size.
This, according to Intel, accounts for a 5% increase in IPC (instructions per clock) by focusing on reducing the wait time for data for the traditional CPU part of the Broadwell processor.
In our initial review of the Broadwell processors, we saw that it was not as straightforward as this. The two CPUs we tested, the i7-5775C and the i5-5675C, are built to a 65W thermal design power, compared to the high end models from Haswell which are at the 84/88W level. This means that for users looking for the next most powerful processor, the base processor frequencies of the Broadwell samples we had are lower and less performant due to frequency, more than any IPC increase could overcome.
Core i7-5775C lining up with the Core i7-4790K
It was difficult for Broadwell to win any CPU focused benchmark from a pure frequency (and TDP) handicap. To add an additional element into the mix, almost every Broadwell's memory cache system is also different:
Intel Desktop Processor Cache Comparison | |||||
L1-D | L1-I | L2 | L3 | L4 | |
Sandy Bridge i7 | 4 x 32 KB | 4 x 32 KB | 4 x 256 KB | 8 MB | |
Ivy Bridge i7 | 4 x 32 KB | 4 x 32 KB | 4 x 256 KB | 8 MB | |
Haswell i7 | 4 x 32 KB | 4 x 32 KB | 4 x 256 KB | 8 MB | |
Broadwell i7 (Desktop / Iris Pro 6200) |
4 x 32 KB | 4 x 32 KB | 4 x 256 KB | 6 MB | 128 MB eDRAM |
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Haswell i5 | 4 x 32 KB | 4 x 32 KB | 4 x 256 KB | 6 MB | |
Broadwell i7 (i7-5700HQ / HD 5600) |
4 x 32 KB | 4 x 32 KB | 4 x 256 KB | 6 MB |
Both the Level 1 and Level 2 caches of each processor are the same, but at Level 3 where Haswell i7 has 8MB, the Broadwell i7 only has 6MB. Aside from the improved branch predictor mentioned above to reduce cache misses, Broadwell also has a separate eDRAM in the CPU package, weighing in at 128MB. This acts as a level 4 cache, having a latency between the L3 and moving out to memory, resulting in less trips out to main memory. This combination of architecture improvements and eDRAM on Broadwell combined with the lower L3 cache size makes it an unknown in memory performance.
I have also included the Haswell i5 and the Broadwell-based i7-5700HQ in this table, showing that the Broadwell i7 L1/L2/L3 cache hierarchy is more akin to a desktop i5 processor and that Broadwell is available without the eDRAM. That being said, the i7-5700HQ is a single processor destined for laptops, making any discrete testing nominally impossible, and taken out of the real-world context for the majority of Broadwell desktop owners.
The reason for Broadwell's eDRAM comes from Intel's ‘Crystal Well’ strategy. Crystal Well is a designation given to a processor which has this eDRAM (and typically a larger integrated graphics package as well). Integrated graphics are historically inhibited by memory bandwidth, having to almost always reach out to main memory to process textures in graphic workloads. The eDRAM allows more data to be stored between the graphics core and the memory, and at a higher memory bandwidth, potentially improving output. By combining the high end integrated graphics with the eDRAM, Intel created these Broadwell processors as the fastest integrated graphics solution available on a socketable (replaceable processor) platform.
That being said, due to Broadwell being the latest product from Intel, and it having the most recent (and expensive) process node, equipped with eDRAM which is a separate die on the package, the Broadwell solutions do not come cheap. The pricing is almost in line with previous Haswell mainstream i7 processors, albeit at the lower thermal design and the beefier integrated graphics. As we determined in the Broadwell Part 1 review, the desktop Broadwell has the absolute integrated performance crown, although an AMD APU system will be significantly more cost effective. Both platforms are hoping that multi-GPU possibilities in DirectX12 have a positive outcome to their solutions.
This Review
We said we'd be back for part 2, and this is it. Here I wanted to cover what we couldn't previously due to early BIOS revisions and limited time testing - specifically looking at how Broadwell performs when overclocking, and whether the Broadwell architecture is truly a step up over previous generations of Intel processors. In the last review our comparison point was the i7-4770K from Intel's Haswell line; for part two we also back tested the i7-3770K from the Ivy Bridge platform and the i7-2600K from Sandy Bridge, covering the four most recent Intel processor architectures dating back to January 2011. We also have data on older benchmarks going back further. All four of the most recent architectures are tested at their stock speeds and at a constant 3 GHz (at 1866 C9) to find how IPC improves. (Incidentally I did find an i7-750 and a Q9550 in my CPU bin for the next two generations back, but have no motherboards for testing our more recent benchmarks. I'll see what I can put together for a mini-piece later in the year.)
Test setup
Test Setup | |||||||||||||||||||||
Processor |
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Motherboards | MSI Z97A Gaming 6 (LGA1150) ASRock Z77 OC Formula (LGA1155) |
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Cooling | Cooler Master Nepton 140XL | ||||||||||||||||||||
Power Supply | OCZ 1250W Gold ZX Series | ||||||||||||||||||||
Memory | G.Skill RipjawsZ 4x4 GB DDR3-1866 9-11-11 Kit | ||||||||||||||||||||
Video Cards | ASUS GTX 980 Strix 4GB MSI GTX 770 Lightning 2GB (1150/1202 Boost) ASUS R7 240 2GB |
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Hard Drive | Crucial MX200 1TB | ||||||||||||||||||||
Optical Drive | LG GH22NS50 | ||||||||||||||||||||
Case | Open Test Bed | ||||||||||||||||||||
Operating System | Windows 7 64-bit SP1 |
Many thanks to
Thank you to AMD for providing us with the R9 290X 4GB GPUs.
Thank you to ASUS for providing us with GTX 980 Strix GPUs and the R7 240 DDR3 GPU.
Thank you to ASRock and ASUS for providing us with some IO testing kit.
Thank you to Cooler Master for providing us with Nepton 140XL CLCs.
Thank you to Corsair for providing us with an AX1200i PSU.
Thank you to Crucial for providing us with MX200 SSDs.
Thank you to G.Skill and Corsair for providing us with memory.
Thank you to MSI for providing us with the GTX 770 Lightning GPUs.
Thank you to OCZ for providing us with PSUs.
Thank you to Rosewill for providing us with PSUs and RK-9100 keyboards.
121 Comments
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plonk420 - Wednesday, August 12, 2015 - link
you "blame" AMD?a fuckup warrants "blame." you can't really "blame" someone or some company for not being smart enough to outwit/outperform the competition.
david_tocker - Tuesday, August 4, 2015 - link
I recently upgraded my i7-920 to a Xeon x5670 in the same board. Less power, more performance, same motherboard. Has USB3 - what else do I need?StevoLincolnite - Monday, August 3, 2015 - link
Same situation as you.Got a 3930K... It has happily sat at 4.8ghz just fine for many many years and still gives Haswell-E a good run for it's money. Only paid $500 AUD at the time too!
That is in stark contrast to the 5930K which is currently $860 AUD... Intel has provided me with ZERO compelling reason to upgrade unless I wish to drop down $1500 for the 5960X, which isn't three times as fast as my 3930K.
It's like they don't want my money!
If Intel had released an 8-core 5930K around the $600 mark I wouldn't have thought twice about upgrading, even if the motherboard and memory drove the prices higher.
Also still got a Core 2 Quad Q6600 rig running at 3.6ghz which handles most tasks fine, it's almost 8 years old now, it has certainly paid for itself and still handles most of the latest games fine.
Flunk - Monday, August 3, 2015 - link
I totally agree with you, 6-cores isn't worth bothering with for what Intel's charging. I'm still holding on to my i5-2500k, which does 4.4 all day at 1.2V (and a bit more if you give it a bit more juice).Jetpil0t - Thursday, August 6, 2015 - link
Haven't even bothered to take my 2500k past 4.0 Ghz leaving all the tuning at stock, I remember back in the day I had er up at 4.6 stable with tweaks, but even then it wasn't really a bottleneck. Humming along at 55c max under load @ 4.0Ghz. Most of these CPUs are much hotter thanks to the IGP as well, making Sandy even more enjoyable. Also why would a K series CPU even ship with integrated graphics in the first place.Samus - Monday, August 3, 2015 - link
I still rock a Asus X58 with a i7-950 (used to be a i7-920) back at the office. Never overclocked, completely stable, still completely competitive with modern PC's 7 years later.Obviously it uses more power (130w vs 80w) to a comparably performance-equivalent Haswell Xeon 1230v3 but the difference is a few dollars a year,
hughlle - Monday, August 3, 2015 - link
And I still rock a tock Q6600 and HD 7750. Plays everything that's on the market just fine :)Jon Tseng - Tuesday, August 4, 2015 - link
yeah I still have QX6850 and GTX 970 and it runs all new gaming releases ultra @1080p smooth as butter.I have a suspicion I'm going to get a decade of use out of this Kentsfield, which is completely nuts (and bad news for Intel!)
Bad Bimr - Monday, August 3, 2015 - link
Same here. I have an Asus x58 motherboard with 24GB CL7 memory. Recently pulled the 4Ghz overclocked i7-920 and replaced it with an $85 Xeon X5675 overclocked to 4.6Ghz. My ancient system will hold it's own against most newer systems. Not going to upgrade until Skylake-E or later.xorfish - Monday, August 3, 2015 - link
Go Xeon, those 6 core chips go for 80$ and perform as well as a 4790k in multithreaded tasks.Got mine to 4.0 Ghz for 24/7.
Also 32nm saves you some power...