A Broadwell Retrospective Review in 2020: Is eDRAM Still Worth It?
by Dr. Ian Cutress on November 2, 2020 11:00 AM ESTPower Consumption
The nature of reporting processor power consumption has become, in part, a dystopian nightmare. Historically the peak power consumption of a processor, as purchased, is given by its Thermal Design Power (TDP, or PL1). For many markets, such as embedded processors, that value of TDP still signifies the peak power consumption. For the processors we test at AnandTech, either desktop, notebook, or enterprise, this is not always the case.
Modern high performance processors implement a feature called Turbo. This allows, usually for a limited time, a processor to go beyond its rated frequency. Exactly how far the processor goes depends on a few factors, such as the Turbo Power Limit (PL2), whether the peak frequency is hard coded, the thermals, and the power delivery. Turbo can sometimes be very aggressive, allowing power values 2.5x above the rated TDP.
AMD and Intel have different definitions for TDP, but are broadly speaking applied the same. The difference comes to turbo modes, turbo limits, turbo budgets, and how the processors manage that power balance. These topics are 10000-12000 word articles in their own right, and we’ve got a few articles worth reading on the topic.
- Why Intel Processors Draw More Power Than Expected: TDP and Turbo Explained
- Talking TDP, Turbo and Overclocking: An Interview with Intel Fellow Guy Therien
- Reaching for Turbo: Aligning Perception with AMD’s Frequency Metrics
- Intel’s TDP Shenanigans Hurts Everyone
In simple terms, processor manufacturers only ever guarantee two values which are tied together - when all cores are running at base frequency, the processor should be running at or below the TDP rating. All turbo modes and power modes above that are not covered by warranty. Intel kind of screwed this up with the Tiger Lake launch in September 2020, by refusing to define a TDP rating for its new processors, instead going for a range. Obfuscation like this is a frustrating endeavor for press and end-users alike.
However, for our tests in this review, we measure the power consumption of the processor in a variety of different scenarios. These include full AVX2/AVX512 (delete as applicable) workflows, real-world image-model construction, and others as appropriate. These tests are done as comparative models. We also note the peak power recorded in any of our tests.
In peak power, the Core i7-5775C sticks to the 65 W value, whereas the Core i5 variant is below its TDP value. This is beyond the 22nm Core i7-4790S which is also a 65 W part.
In real-world tests, first up is our image-model construction workload, using our Agisoft Photoscan benchmark. This test has a number of different areas that involve single thread, multi-thread, or memory limited algorithms.
For Photoscan, the Core i7 spends its 'real world' time around 60 W, but does momentarily spike up above that 60 W mark. The Core i5 by comparison doesn't even touch 50 W.
The second test is from y-Cruncher, which is our AVX2/AVX512 workload. This also has some memory requirements, which can lead to periodic cycling with systems that have lower memory bandwidth per core options.
We're seeing some slight variation in power as the y-Cruncher algortihm moves out to DRAM movement over compute, however both processors seem to be hitting either their power limits or just a natural peak power consumption.
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bernstein - Monday, November 2, 2020 - link
GDDR6 would be ideally suited as an L4 CPU cache... it has >500GB/s throughput and relatively low cost...e36Jeff - Monday, November 2, 2020 - link
Sure, if you build a 256-bit bus and somehow cram 8 GDDR6 chips onto the CPU package. You'd also be losing 30-40W of TDP to that.This is an application that HBM2 would be much better for. You can easily cram up to 4GB into the package with a much lower TDP impact and still get your 500+GB/s throughput. The biggest issue for this is going to be the impact of having to add in another memory controller and the associated die space and power that it eats up.
FreckledTrout - Monday, November 2, 2020 - link
This is also how I see it playing out. Certainly by the time Intel/AMD switch to using GAAFET maybe before. You just need a couple die shrinks that bring densities up and power down.bernstein - Monday, November 2, 2020 - link
scratch that, GDDR6 has much too high latency...stanleyipkiss - Monday, November 2, 2020 - link
The 5775C was ahead of its time. Don't know why they didn't go down that rabbit hole (of increasing the size with each gen)hecksagon - Monday, November 2, 2020 - link
Adding an extra 84mm2 of die area is a recipe for margin erosion, especially when the benefit is situational.CrispySilicon - Monday, November 2, 2020 - link
Well, I use a 5775C for my main home PC (using it now) and it's more than that. Broadwell was designed for low power. It doesn't run well over 4Ghz and it's not made to.My rig idles at about 800mhz, clocks up to 4ghz on all cores, 2ghz on the edram, and 2ghz on DDR3L (overclocked 1866 hyperx fury), yes, 3L, becuase THAT'S where the magic happens. Low power performance.
I've also used TridentX 2400CL10 modules in it, not worth the higher voltage.
I'm going to upgrade finally next year. CXL and DDR5 will finally retire this diamond in the rough.
Retest with nothing in the BIOS changed except the eDRAM multiplier to 20 and see what happens.
Notmyusualid - Wednesday, November 4, 2020 - link
I usually run my Broadwell at 4.4GHz 24/7. However I have a failed bios battery so using the m/b default 4.0GHz overclock settings today. I don't let mine idle at low speeds, its High Performance mode only & I only boot the Desktop for gaming, or Software Define Radio. Both of which want GHz.Memory is Vengeance LED 3200MHz (CL15 & only stable at 3000MHz, XMP is not stable either), and 32GB is currently installed.
Given;
C:\Windows\System32>winsat mem
Windows System Assessment Tool
> Running: Feature Enumeration ''
> Run Time 00:00:00.00
> Running: System memory performance assessment ''
> Run Time 00:00:05.45
> Memory Performance 54386.55 MB/s
> Total Run Time 00:00:06.65
I think that is why my Broadwell missed out on any eDRAM - it wasn't necessary.
Dolphin runs about 35x seconds, as I remember it.
6950X running cool in 2020...
MrCommunistGen - Monday, November 2, 2020 - link
HA. Epic timing. Just starting to read this now, but I recently built a system with a Broadwell-based Xeon E3 chip I got for cheap on eBay. Mostly just because I wanted to play with a chip that had eDRAM and the price of entry for an i5 or i7 has remained pretty high.This will be a very interesting read!
alufan - Monday, November 2, 2020 - link
News all day as long as its about Intel so it seems on here said it before and have seen nothing since to change my mind