AMD Zen Microarchitecture: Dual Schedulers, Micro-Op Cache and Memory Hierarchy Revealed
by Ian Cutress on August 18, 2016 9:00 AM ESTDeciphering the New Cache Hierarchy
The cache hierarchy is a significant deviation from recent previous AMD designs, and most likely to its advantage. The L1 data cache is both double in size and increased in associativity compared to Bulldozer, as well as being write-back rather than write-through. It also uses an asymmetric load/store implementation, identifying that loads happen more often than stores in the critical paths of most work flows. The instruction cache is no longer shared between two cores as well as doubling in associativity, which should decrease the proportion of cache misses. AMD states that both the L1-D and L1-I are low latency, with details to come.
The L2 cache sits at half a megabyte per core with 8-way associativity, which is double that of Intel’s Skylake which has 256 KB/core and is only 4-way. On the other hand, Intel’s L3/LLC on their high-end Skylake SKUs is at 2 MB/core or 8 MB/CPU, whereas Zen will feature 1 MB/core and both are at 16-way associativity.
Edit 7:18am: Actually, the slide above is being slightly evasive in its description. It doesn't say how many cores the L3 cache is stretched over, or if there is a common LLC between all cores in the chip. However, we have recieved information from a source (which can't be confirmed via public AMD documents) that states that Zen will feature two sets of 8MB L3 cache between two groups of four cores each, giving 16 MB of L3 total. This would means 2 MB/core, but it also implies that there is no last-level unified cache in silicon across all cores, which Intel has. The reasons behind something like this is typically to do with modularity, and being able to scale a core design from low core counts to high core counts. But it would still leave a Zen core with the same L3 cache per core as Intel.
| Cache Levels | ||||
| Bulldozer FX-8150 |
Zen | Broadwell-E i7-6950X |
Skylake i7-6700K |
|
| L1 Instruction | 64 KB 2-way per module |
64 KB 4-way | 32 KB 8-way | 32 KB 8-way |
| L1 Data | 16 KB 4-way Write Through |
32 KB 8-way Write Back |
32 KB 8-way Write-Back |
32 KB 8-way Write-Back |
| L2 | 2 MB 16-way per module |
512 KB 8-way | 256 KB 8-way | 256 KB 4-way |
| L3 | 1 MB/core 64-way |
1 or 2 MB/core ? 16-way |
2.5 MB/core 16/20-way |
2 MB/core 16-way |
What this means, between the L2 and the L3, is that AMD is putting more lower level cache nearer the core than Intel, and as it is low level it becomes separate to each core which can potentially improve single thread performance. The downside of bigger and lower (but separate) caches is how each of the cores will perform snoop in each other’s large caches to ensure clean data is being passed around and that old data in L3 is not out-of-date. AMD’s big headline number overall is that Zen will offer up to 5x cache bandwidth to a core over previous designs.
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Kevin G - Saturday, August 20, 2016 - link
Google is porting their internal software but they're not moving production system unless there is a clear reason. (And for some specific applications, there are some clear reasons.)Google doesn't want to be married to any particular architecture.
BillBear - Saturday, August 20, 2016 - link
As of April, they seem to have already ported their software stack to POWER and to be in the process of designing server hardware with Rackspace with the intention of making those designs public under the Open Compute Project.http://www.pcworld.com/article/3053092/ibms-power-...
BillBear - Saturday, August 20, 2016 - link
I should be clear that I'm not saying Google intends to abandon x86. They are simply talking about POWER based servers becoming a first class citizen in their infrastructure.TheinsanegamerN - Saturday, August 20, 2016 - link
Crossing fingers for a great 35 watt APU. The iGPU space in laptops has been stagnant since trinity. and it is abundantly clear that intel cant supply iris pro parts in any meaningful capacity.Now that AMD supports linux properly with polaris, all we need is a polaris+zen APU for laptops, and I can finally move off of windows altogether.
Michael Bay - Sunday, August 21, 2016 - link
Why would you even need a gpu in a laptop running specialized OS in the first place? Games aren`t being ported outside of token cases and rendering/drawing/general office applications are a sad joke.Networking is where it`s good at, and you don`t need anything over perfunctory graphics there.
Gigaplex - Monday, August 22, 2016 - link
Linux is quite the opposite of a specialized OS. It's probably the most versatile platform out there.Michael Bay - Monday, August 22, 2016 - link
I see it being said a lot, but what`s the point if software is so bad with no hope of improvement? You can`t reasonably compete with Adobe if there are three people on your team doing this in their spare time, same goes for Zbrush and any other professional content creation tool. Much better to focus where you actually can lead.asoltesz - Sunday, August 28, 2016 - link
"with no hope of improvement" is nonsense for one tracking the Linux world even if only casually.First of all the open source applications have matured a lot. E.g. I could do everything I wanted with Kdenlive as good as the built in movie editor of OSX. (Consumer level, bit still)
For certain niches, oss is now as good as the commercial competition (eg Krita for digital painting)
A lot of newer applications now have proper Linux support (E.g. Slack) because they were created with platform independent toolkits.
As for the base OS and desktop, I find desktop Linux way more powerful and sophisticated than either Windows or OSX. My ws runs KDE Plasma 5 on an Ubuntu base and it is better looking , faster and more stable than my OSX ElCap laptop.
BrokenCrayons - Monday, August 22, 2016 - link
Check Steam. The last time I looked, about 2,700 games of the 11,000 were supported under Linux. Then there's quite a few that play nicely under WINE + PlayOnLinux. Native gaming on Linux has dramatically improved in the last 4 years. It seems as though momentum is building still rather than declining. Office applications have come a long way as well thanks to the folks behind LibreOffice. I've been using it as a personal office suite since the fork from OpenOffice and it's made impressive progress. Formatting MS Office documents is still a minor sticking point, but the number of differences I see when moving files between office suites now are very small with most cases being oddball outliers that require obscure capabilities of Microsoft's suites. Rendering has never been a problem on Linux platforms. Drawing though, in my opinion is still a shortcoming. GIMP is a miserable piece of software to work with and remains one of the only image editing options for Linux users.However, I doubt my comment will change your mind. Much like the people who use a $ when they talk about Microsoft, you insist on using the word "loonix" in many of your posts. It shows a very strong bias supported by a framework of childish emotional investment in something as meaningless as software on a computer someone else owns.
Michael Bay - Monday, August 22, 2016 - link
>2700 indie nongamesUh-uh. Wake me up when AAA comes in any significant number.
>WINE
Are you joking.
>Libre
Okay, now I know you are.
>GIMP
At least here we can agree.