The AMD Zen and Ryzen 7 Review: A Deep Dive on 1800X, 1700X and 1700
by Ian Cutress on March 2, 2017 9:00 AM ESTThe Core Complex, Caches, and Fabric
Many core designs often start with an initial low-core-count building block that is repeated across a coherent fabric to generate a large number of cores and the large die. In this case, AMD is using a CPU Complex (CCX) as that building block which consists of four cores and the associated caches.
Each core will have direct access to its private L2 cache, and the 8 MB of L3 cache is, despite being split into blocks per core, accessible by every core on the CCX with ‘an average latency’ also L3 hits nearer to the core will have a lower latency due to the low-order address interleave method of address generation.
The L3 cache is actually a victim cache, taking data from L1 and L2 evictions rather than collecting data from prefetch/demand instructions. Victim caches tend to be less effective than inclusive caches, however Zen counters this by having a sufficiency large L2 to compensate. The use of a victim cache means that it does not have to hold L2 data inside, effectively increasing its potential capacity with less data redundancy.
It is worth noting that a single CCX has 8 MB of cache, and as a result the 8-core Zen being displayed by AMD at the current events involves two CPU Complexes. This affords a total of 16 MB of L3 cache, albeit in two distinct parts. This means that the true LLC for the entire chip is actually DRAM, although AMD states that the two CCXes can communicate with each other through the custom fabric which connects both the complexes, the memory controller, the IO, the PCIe lanes etc.
The cache representation shows L1 and L2 being local to each the core, followed by 8MB of L3 split over several cores. AMD states that the L1 and L2 bandwidth is nearly double that of Excavator, with L3 now up to 5x for bandwidth, and that this bandwidth will help drive the improvements made on the prefetch side. AMD also states that there are large queues in play for L1/L2 cache misses.
One interesting story is going to be how AMD’s coherent fabric works. For those that follow mobile phone SoCs, we know fabrics and interconnects such as CCI-400 or the CCN family are optimized to take advantage of core clusters along with the rest of the chip. A number of people have speculated that the fabric used in AMD’s new design is based on HyperTransport, however AMD has confirmed that they are using a superset HyperTransport here for Zen, and that the Infinity fabric design is meant to be high bandwidth, low latency, and be in both Zen and Vega as well as future products. Almost similar to the CPU/GPU roadmaps, the Fabric has its own as well.
Ultimately the new fabric involves a series of control and data passing structures, with the data passing enabling third-party IP in custom designs, a high-performance common bus for large multi-unit (CPU/GPU) structures, and socket to socket communication. The control elements are an extension of power management, enabling parts of the fabric to duty cycle when not in use, security by way of memory management and detection, and test/initialization for activities such as data prefetch.
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mapesdhs - Sunday, March 5, 2017 - link
If you have a Q6600, I can understand that, but the QX9650 ain't too bad. ;)Marburg U - Monday, March 6, 2017 - link
I'm on a Q9550 running at 3.8 for the past 6 years. I could still run modern games at 1050p, with a r9 270x, but that's the best i can squeeze out of it. Mind that i'm still on DDR2 (my motherboard turns 10 in a few months). I really want to embrace a ultra wide monitor.mapesdhs - Monday, March 6, 2017 - link
Moving up to 2560x1440 may indeed benefit from faster RAM, but it probably depends on the game. Likewise, CPU dependencies vary, and they can lessen at higher resolutions, though this isn't always the case. Still, good point about DDR2 there. To what kind of GPU were you thinking of upgrading? Highend like 1080 Ti? Mid-range? Used GTX 980s are a good deal these days, and a bunch of used 980 Tis will likely hit the market shortly. I've tested 980 SLI with older platforms, actually not too bad, though I've not done tests with my QX9650 yet, started off at the low end to get through the pain. :D (P4/3.4 on an ASUS Striker II Extreme, it's almost embarassing)Ian.
Meditari - Monday, March 6, 2017 - link
I'm actually using a Q9550 that's running at 3.8 as well. I have a 980ti and it can do 4k, albeit at 25-30fps in newer games like Witcher 3. Fairly certain a 1080ti would work great with a Q9550, but I feel like the time for these chips is coming to an end. Still incredible that a 8 year old chip can still hold it's own by just upgrading the GPUmapesdhs - Tuesday, March 7, 2017 - link
Intriguing! Many people don't even try to use such a card on an older mbd, they just assume from sites reviews that it's not worth doing. Can you run 3DMark11/13? What results do you get? You won't be able to cite the URLs here directly, but you can mention the submission numbers and I can compare them to my 980 Ti running on newer CPUs (the first tests I do with every GPU I obtain are with a 5GHz 2700K, at which speed it has the same multithreaded performance as a stock 6700K).What do you get for CB 11.5 and CB R15 single/multi?
What mbd are you using? I ask because some later S775 mbds did use DDR3, albeit not at quite the speeds possible with Z68, etc. In other words, you could move the parts on a better mbd as an intermediate step, though finding such a board could be difficult. Hmm, given the value often placed on such boards, it'd probably be easier to pick up a used 3930K and a board to go with it, that would be fairly low cost.
Or of course just splash for a 1700X. 8)
Ian.
Notmyusualid - Tuesday, March 7, 2017 - link
Welcome to the 21:9 fan club brother.But be careful of the 1920x1080 screens, my brother's 21:9 doesn't look half as good as my 3440x1440 screen.. It just needs that little bit more verticle resoultion.
My pals 4k screen is lovely, and brings his 4GB 980 GTX to its knees. Worse aspect ratio (in my opinion), and too many pixels (for now) to draw.
Careful of second-hand purchases too, many panels with backlight-bleed issues out there, and they are returns for that reason, again, in my opinion.
AnnonymousCoward - Monday, March 6, 2017 - link
Long story short:20% lower single-thread than Intel
70% higher multi-thread due to 8 cores
$330-$500
Mugur - Tuesday, March 7, 2017 - link
Actually, on average -6.8% IPC versus Kaby Lake (at the same frequency) - I believe this came directly from AMD. Add to this a lower grade 14nm process (GF again) that is biting AMD again and again (see last year RX480). Motherboard issues (memory, HPET), OS/application issues (SMT, lack of optimizations).All in all, I'm really impressed of what they achieved with such obstacles.
AnnonymousCoward - Tuesday, March 7, 2017 - link
Just looking at CineBench at a given TDP and price, AMD is 20% lower. That's the high level answer, regardless of IPC * clock frequency. I agree it's a huge win for AMD, and for users who need multicore performance.Cooe - Monday, March 1, 2021 - link
Maybe compare to Intel's Broadwell-E chips with actually similar core counts.... -_-