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 ESTFetch
For Zen, AMD has implemented a decoupled branch predictor. This allows support to speculate on incoming instruction pointers to fill a queue, as well as look for direct and indirect targets. The branch target buffer (BTB) for Zen is described as ‘large’ but with no numbers as of yet, however there is an L1/L2 hierarchical arrangement for the BTB. For comparison, Bulldozer afforded a 512-entry, 4-way L1 BTB with a single cycle latency, and a 5120 entry, 5-way L2 BTB with additional latency; AMD doesn’t state that Zen is larger, just that it is large and supports dual branches. The 32 entry return stack for indirect targets is also devoid of entry numbers at this point as well.
The decoupled branch predictor also allows it to run ahead of instruction fetches and fill the queues based on the internal algorithms. Going too far into a specific branch that fails will obviously incur a power penalty, but successes will help with latency and memory parallelism.
The Translation Lookaside Buffer (TLB) in the branch prediction looks for recent virtual memory translations of physical addresses to reduce load latency, and operates in three levels: L0 with 8 entries of any page size, L1 with 64 entries of any page size, and L2 with 512 entries and support for 4K and 256K pages only. The L2 won’t support 1G pages as the L1 can already support 64 of them, and implementing 1G support at the L2 level is a more complex addition (there may also be power/die area benefits).
When the instruction comes through as a recently used one, it acquires a micro-tag and is set via the op-cache, otherwise it is placed into the instruction cache for decode. The L1-Instruction Cache can also accept 32 Bytes/cycle from the L2 cache as other instructions are placed through the load/store unit for another cycle around for execution.
Decode
The instruction cache will then send the data through the decoder, which can decode four instructions per cycle. As mentioned previously, the decoder can fuse operations together in a fast-path, such that a single micro-op will go through to the micro-op queue but still represent two instructions, but these will be split when hitting the schedulers. The purpose of this allows the system to fit more into the micro-op queue and afford a higher throughput when possible.
The new Stack Engine comes into play between the queue and the dispatch, allowing for a low-power address generation when it is already known from previous cycles. This allows the system to save power from going through the AGU and cycling back around to the caches.
Finally, the dispatch can apply six instructions per cycle, at a maximum rate of 6/cycle to the INT scheduler or 4/cycle to the FP scheduler. We confirmed with AMD that the dispatch unit can simultaneously dispatch to both INT and FP inside the same cycle, which can maximize throughput (the alternative would be to alternate each cycle, which reduces efficiency). We are told that the operations used in Zen for the uOp cache are ‘pretty dense’, and equivalent to x86 operations in most cases.
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Crono - Thursday, March 2, 2017 - link
A Hero Has RyzenSweeprshill - Thursday, March 2, 2017 - link
Lived up to the hype. Ryzen is a beast. Intel needs massive price cuts on their 2011-v3 chips. Well done AMD, best price/performance CPUs on the market and as fast or faster than Intel performance.sans - Thursday, March 2, 2017 - link
Hey, what you have found which features improving on AMD's crap has been found in Intel's products for years.Nem35 - Thursday, March 2, 2017 - link
Yeah, and it's beating the Intel. Funny, right?Sweeprshill - Thursday, March 2, 2017 - link
Yeah these new AMD chips are monsters. Wondering how large the price cuts are that Intel will bring to their 2011-v3 chips to compete.czerro - Friday, March 3, 2017 - link
Intel already slashed prices pretty drastically 4 days ago, to kinda deflate Ryzen's release. Before price cuts, Ryzen had a huge price and performance advantage at all metrics, and Intel would have looked ridiculous.I can't believe people aren't reporting the price-cutting right before Ryzen release more. Intel only did it to save face on graphs and confuse people. Ryzen definitely had Intel by the balls a week ago before the price cuts.
It's great that we all have options now, but this really smeared Ryzen's release in a cheap way that anybody can point out all those Intel chips were 100-200 dollars more expensive less than a WEEK ago.
SodaAnt - Saturday, March 4, 2017 - link
No, Intel hasn't slashed prices. There was a sale at microcenter a few days back, but there's no across the board official price cut on Intel chips.Notmyusualid - Monday, March 6, 2017 - link
@ SodaAntAgreed, I see no Intel price drops either.
Notmyusualid - Friday, March 3, 2017 - link
@ Nem35Incomplete review.
After seeing a gaming-focused review, I'd say the AMD procs are just OK. I welcome AMD is back with a fighting chance, but about half my purchase choice will be game-inspired.
Quote:
"For gaming, it’s a hard pass. We absolutely do not recommend the 1800X for gaming-focused users or builds, given i5-level performance at two times the price."
I'm not a 'fanboi', as I'd have no trouble fitting a 1700X in a build I wouldn't game in. But otherwise, like another reviewer said, its a hard pass.
Alexvrb - Saturday, March 4, 2017 - link
For gaming builds the upcoming Ryzen 5 and 3 series will offer a lot more bang for your buck and will compete much more aggressively. However, the Ryzen 7 still offers decent gaming performance and excellent performance everywhere else. The gobs of cores may come in handy in the future too, even in games - as more threads will be available on more rigs, devs will take notice. This year AMD is definitely lowering the pricing for 8-16 thread processors, clearing a path for the future of gaming.With that being said I still think that when strictly considering gaming, their Ryzen 3/5 quadcore models will be a far better value, especially as current-gen games aren't often built in such a way that they can take advantage of the Ryzen 7.