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 ESTExecution, Load/Store, INT and FP Scheduling
The execution of micro-ops get filters into the Integer (INT) and Floating Point (FP) parts of the core, which each have different pipes and execution ports. First up is the Integer pipe which affords a 168-entry register file which forwards into four arithmetic logic units and two address generation units. This allows the core to schedule six micro-ops/cycle, and each execution port has its own 14-entry schedule queue.
The INT unit can work on two branches per cycle, but it should be noted that not all the ALUs are equal. Only two ALUs are capable of branches, one of the ALUs can perform IMUL operations (signed multiply), and only one can do CRC operations. There are other limitations as well, but broadly we are told that the ALUs are symmetric except for a few focused operations. Exactly what operations will be disclosed closer to the launch date.
The INT pipe will keep track of branching instructions with differential checkpoints, to cut down on storing redundant data between branches (saves queue entries and power), but can also perform Move Elimination. This is where a simple mov command between two registers occurs – instead of inflicting a high energy loop around the core to physically move the single instruction, the core adjusts the pointers to the registers instead and essentially applies a new mapping table, which is a lower power operation.
Both INT and FP units have direct access to the retire queue, which is 192-entry and can retire 8 instructions per cycle. In some previous x86 CPU designs, the retire unit was a limiting factor for extracting peak performance, and so having it retire quicker than dispatch should keep the queue relatively empty and not near the limit.
The Load/Store Units are accessible from both AGUs simultaneously, and will support 72 out-of-order loads. Overall, as mentioned before, the core can perform two 16B loads (2x128-bit) and one 16B store per cycle, with the latter relying on a 44-entry Store queue. The TLB buffer for the L2 cache for already decoded addresses is two level here, with the L1 TLB supporting 64-entry at all page sizes and the L2 TLB going for 1.5K-entry with no 1G pages. The TLB and data pipes are split in this design, which relies on tags to determine if the data is in the cache or to start the data prefetch earlier in the pipeline.
The data cache here also has direct access to the main L2 cache at 32 Bytes/cycle, with the 512 KB 8-way L2 cache being private to the core and inclusive. When data resides back in L1 it can be processed back to either the INT or the FP pipes as required.
Moving onto the floating point part of the core, and the first thing to notice is that there are two scheduling queues here. These are listed as ‘schedulable’ and ‘non-schedulable’ queues with lower power operation when certain micro-ops are in play, but also allows the backup queue to sort out parts of the dispatch in advance via the LDCVT. The register file is 160 entry, with direct FP to INT transfers as required, as well as supporting accelerated recovery on flushes (when data is written to a cache further back in the hierarchy to make room).
The FP Unit uses four pipes rather than three on Excavator, and we are told that the latency in Zen is reduced as well for operations (though more information on this will come at a later date). We have two MUL and two ADD in the FP unit, capable of joining to form two 128-bit FMACs, but not one 256-bit AVX. In order to do AVX, the unit will split the operations accordingly. On the counter side each core will have 2 AES units for cryptography as well as decode support for SSE, AVX1/2, SHA and legacy mmx/x87 compliant code.
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BurntMyBacon - Friday, March 3, 2017 - link
@Gothmoth: "gamer... as if the world is only full with idiotic people who waste their lives playing shooter or RPG´s."PC Gaming happens to be one of the few growing areas in the PC market. Not everyone games, but for those that do, the 7700K is still worth considering. Dropping $500 on the 1800X may not be the best call for those that don't take advantage of the parallelism. Of course, the 1800X wasn't really meant for people who can't take advantage of the parallelism. AMD will have lower cost narrower processors to address that gap. I'm curious as to how the performance/price equation will stand once AMD releases their upper end 6c/12t and 4c/8t processors.
Beany2013 - Friday, March 3, 2017 - link
Sod the 1800X - I need a new VM server, and if I want all the threads (sixteen), I can either drop £450 on a Xeon E5 2620 at 2.1-3ghz (cheapest Intel 16 thread option I can find), or I can spend £100 less, and get a Ryzen 7 1700 (3.0-3.7ghz) and put that extra money towards more RAM so I can run more VMs and get more work done.For those of us who aren't high end gamers - which is basically almost everyone, and a far more significant market - these chips may well give Intel a bloody nose in the workstation space; AMD have confirmed they'll use ECC RAM quite happily.
Photographers, videographers, CAD-CAM, developers etc are a bigger market in terms of raw units than high end gamers, and these chips look like being a pretty compelling option as it stands.
Steven R
Beany2013 - Friday, March 3, 2017 - link
(VM server for home, I should have noted - for work, I'll see how the Ryzen based opterons and supermicro mobos etc pan out - money is important in these factors, but I'm not a moron, and I'm not going to run production gear on gaming hardware, natch....)BurntMyBacon - Friday, March 3, 2017 - link
@Beany2013: "I need a new VM server, and if I want all the threads (sixteen), I can either drop £450 on a Xeon E5 2620 at 2.1-3ghz (cheapest Intel 16 thread option I can find), or I can spend £100 less, and get a Ryzen 7 1700 (3.0-3.7ghz) and put that extra money towards more RAM so I can run more VMs and get more work done."It is clear by this statement that you fall into the category of people that can take advantage of the parallelism. Therefore, my statement doesn't apply to your presented in the slightest.
I don't disagree that the Ryzen 7 series has a lot to offer to a lot of people (myself included). If I were in the market today, I'd be looking long and hard at an R7 1700X. The minor drop in gaming performance is less significant to me than the increase in performance for many other tasks I use my computer for. I do a little bit of dabbling in a lot of different things (most of which benefit from high thread count). I have noticed that for the set of applications I have open simultaneously and the tasks I have running, my computer is more responsive with more cores or threads, but single threaded performance is still important to the individual tasks.
In my workflow: (i3 < i5/FX-8xxx < i7 <? R7)
My point was that there is in fact a not so insignificant market of people putting computers together for the primary purpose of gaming. This market appears, by all metrics, to be growing. For this market, Intel's i7-7700K or better yet i5-7600K are still viable options that provide better performance/price than AMD's current options. I'll repeat: "AMD will have lower cost narrower processors to address that gap. I'm curious as to how the performance/price equation will stand once AMD releases their upper end 6c/12t and 4c/8t processors."
Cooe - Sunday, February 28, 2021 - link
"or better yet i5-7600K"Arguably the most short-sited statement in this entire comments section lol. The 4c/4t i5's had roughly equal gaming performance to Ryzen at launch but with ZERO headroom left for the future. This is why the i5-7600K gets absolutely freaking ROFLSTOMPED by the R5 1600 in modern titles/game engines.
JMB1897 - Friday, March 3, 2017 - link
Compelling, but I don't think it's totally there yet. I'd be worried about the memory issues. Increased latency as you add more DIMMs and dual vs quad channel. I'd spend that extra 100 on a Xeon personally.Sttm - Friday, March 3, 2017 - link
Thats who buys off the shelf CPUs thats cost $$$, Gamers. Thats who AMD needs to please with their product. GAMERS. Thats why AMD's stock has been tanking since Ryzen reviews went up, because GAMERS are the demographic that matters when it comes to performance CPU sales.deltaFx2 - Saturday, March 4, 2017 - link
@Sttm: You have an inflated opinion of the impact of gamers. No, AMD's stock isn't tanking because of gamers. I suggest you also look at Nvidia's stock, which is well down from its high of ~120, to ~98. Wed-Friday, Nvidia dropped from 105 to 98, and it dipped below that to ~96 at one point. That's roughly 7-8%. The two stocks are often correlated on drops, with AMD amplifying nvidia's drop. Both do GPUs, see? Some people make tonnes of money shorting AMD (and in recent times have lost their shirt doing so).Here's the truth: All Desktop, as per Lisa Su, is a 5 bn TAM market and gaming is part of this (let's say 50%). Nothing to scoff at, sure, but compared to laptop and server, it's a rounding error. There's NOTHING in these tests/reviews to suggest that AMD will suck in those markets; in fact, quite the opposite: power looks good, perf looks good. AMD's stock (long term) won't tank on the whims of gamers. They help get the mindshare, which is the only reason they're worth catering to (they tend to be a vocal, passionate, and sometimes irrational lot. You won't see datacenter gurus doing the stuff that gamers do. They certainly won't shoot each other over whose GPU is the best).
cmdrdredd - Saturday, March 4, 2017 - link
Believe it or not there are millions of people worldwide who pretty much use their PC for two things. The internet (web browsing, email etc) and gaming. You don't need 16 threads to check email and read forums either so gaming performance is going to be critical. It's not just the CPU performance, it's the entire platform that contributes to Gaming related performance.sans - Thursday, March 2, 2017 - link
Yeah, stick with Intel because Intel is the standard and its products are the best for each respective market. AMD is a total failure.