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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krowes - Monday, November 2, 2020 - link
CL22 memory for the Ryzen setup? Makes absolutely no sense.Ian Cutress - Tuesday, November 3, 2020 - link
That's JEDEC standard.Khenglish - Monday, November 2, 2020 - link
Was anyone else bothered by the fact that Intel's highest performing single thread CPU is the 1185G7, which is only accessible in 28W tiny BGA laptops?Also the 128mb edram cache does seem to make on average a 10% improvement over the edramless 4790S at the same TDP. I would love to see edram on more cpus. It's so rare to need more than 8 cores. I'd rather have 8 cores with edram than 16+ cores and no edram.
ichaya - Monday, November 2, 2020 - link
There's definitely a cost trade-off involved, but with an I/O die since Zen 2, it seems like AMD could just spin up a different I/O die, and justify the cost easily by selling to HEDT/Workstation/DC.Notmyusualid - Wednesday, November 4, 2020 - link
Chalk me up as 'bothered'.zodiacfml - Monday, November 2, 2020 - link
Yeah but Intel is about squeezing the last dollar in its products for a couple of years now.Endymio - Monday, November 2, 2020 - link
CPU register-> 3 levels of cache -> eDRAM -> DRAM -> Optane -> SSD -> Hard Drive.The human brain gets by with 2 levels of storage. I really don't feel that computers should require 9. The entire approach needs rethinking.
Tomatotech - Tuesday, November 3, 2020 - link
You remember everything without writing down anything? You remarkable person.The rest of us rely on written materials, textbooks, reference libraries, wikipedia, and the internet to remember stuff. If you jot down all the levels of hierarchical storage available to the average degree-educated person, it's probably somewhere around 9 too depending on how you count it.
Not everything you need to find out is on the internet or in books either. Data storage and retrieval also includes things like having to ask your brother for Aunt Jenny's number so you can ring Aunt Jenny and ask her some detail about early family life, and of course Aunt Jenny will tell you to go and ring Uncle Jonny, but she doesn't have Jonny's number, wait a moment while she asks Max for it and so on.
eastcoast_pete - Tuesday, November 3, 2020 - link
You realize that the closer the cache is to actual processor speed, the more demanding the manufacturing gets and the more die area it eats. That's why there aren't any (consumer) CPUs with 1 or more MB of L1 Cache. Also, as Tomatotech wrote, we humans use mnemonic assists all the time, so the analogy short-term/long-term memory is incomplete. Writing and even drawing was invented to allow for longer-term storage and easier distribution of information. Lastly, at least IMO, it boils down to cost vs. benefit/performance as to how many levels of memory storage are best, and depends on the usage scenario.Oxford Guy - Monday, November 2, 2020 - link
Peter Bright of Ars in 2015:"Intel’s Skylake lineup is robbing us of the performance king we deserve. The one Skylake processor I want is the one that Intel isn't selling.
in games the performance was remarkable. The 65W 3.3-3.7GHz i7-5775C beat the 91W 4-4.2GHz Skylake i7-6700K. The Skylake processor has a higher clock speed, it has a higher power budget, and its improved core means that it executes more instructions per cycle, but that enormous L4 cache meant that the Broadwell could offset its disadvantages and then some. In CPU-bound games such as Project Cars and Civilization: Beyond Earth, the older chip managed to pull ahead of its newer successor.
in memory-intensive workloads, such as some games and scientific applications, the cache is better than 21 percent more clock speed and 40 percent more power. That's the kind of gain that doesn't come along very often in our dismal post-Moore's law world.
Those 5775C results tantalized us with the prospect of a comparable Skylake part. Pair that ginormous cache with Intel's latest-and-greatest core and raise the speed limit on the clock speed by giving it a 90-odd W power envelope, and one can't help but imagine that the result would be a fine processor for gaming and workstations alike. But imagine is all we can do because Intel isn't releasing such a chip. There won't be socketed, desktop-oriented eDRAM parts because, well, who knows why.
Intel could have had a Skylake processor that was exciting to gamers and anyone else with performance-critical workloads. For the right task, that extra memory can do the work of a 20 percent overclock, without running anything out of spec. It would have been the must-have part for enthusiasts everywhere. And I'm tremendously disappointed that the company isn't going to make it."
In addition to Bright's comments I remember Anandtech's article that showed the 5675C beating or equalling the 5775C in one or more gaming tests, apparently largely due to the throttling due to Intel's decision to hobble Broadwell with such a low TDP.