A Quick Note on Architecture & Features

With pages upon pages of architectural documents still to get through in only a few hours, for today’s launch news I’m not going to have the time to go in depth on new features or the architecture. So I want to very briefly hit the high points on what the major features are, and also provide some answers to what are likely to be some common questions.

Starting with the architecture itself, one of the biggest changes for RDNA is the width of a wavefront, the fundamental group of work. GCN in all of its iterations was 64 threads wide, meaning 64 threads were bundled together into a single wavefront for execution. RDNA drops this to a native 32 threads wide. At the same time, AMD has expanded the width of their SIMDs from 16 slots to 32 (aka SIMD32), meaning the size of a wavefront now matches the SIMD size. This is one of AMD’s key architectural efficiency changes, as it helps them keep their SIMD slots occupied more often. It also means that a wavefront can be passed through the SIMDs in a single cycle, instead of over 4 cycles on GCN parts.

In terms of compute, there are not any notable feature changes here as far as gaming is concerned. How things work under the hood has changed dramatically at points, but from the perspective of a programmer, there aren’t really any new math operations here that are going to turn things on their head. RDNA of course supports Rapid Packed Math (Fast FP16), so programmers who make use of FP16 will get to enjoy those performance benefits.

With a single exception, there also aren’t any new graphics features. Navi does not include any hardware ray tracing support, nor does it support variable rate pixel shading. AMD is aware of the demands for these, and hardware support for ray tracing is in their roadmap for RDNA 2 (the architecture formally known as “Next Gen”). But none of that is present here.

The one exception to all of this is the primitive shader. Vega’s most infamous feature is back, and better still it’s enabled this time. The primitive shader is compiler controlled, and thanks to some hardware changes to make it more useful, it now makes sense for AMD to turn it on for gaming. Vega’s primitive shader, though fully hardware functional, was difficult to get a real-world performance boost from, and as a result AMD never exposed it on Vega.

Unique in consumer parts for the new 5700 series cards is support for PCI Express 4.0. Designed to go hand-in-hand with AMD’s Ryzen 3000 series CPUs, which are introducing support for the feature as well, PCIe 4.0 doubles the amount of bus bandwidth available to the card, rising from ~16GB/sec to ~32GB/sec. The real world performance implications of this are limited at this time, especially for a card in the 5700 series’ performance segment. But there are situations where it will be useful, particularly on the content creation side of matters.

Finally, AMD has partially updated their display controller. I say “partially” because while it’s technically an update, they aren’t bringing much new to the table. Notably, HDMI 2.1 support isn’t present – nor is more limited support for HDMI 2.1 Variable Rate Refresh. Instead, AMD’s display controller is a lot like Vega’s: DisplayPort 1.4 and HDMI 2.0b, including support for AMD’s proprietary Freesync-over-HDMI standard. So AMD does have variable rate capabilities for TVs, but it isn’t the HDMI standard’s own implementation.

The one notable change here is support for DisplayPort 1.4 Display Stream Compression. DSC, as implied by the name, compresses the image going out to the monitor to reduce the amount of bandwidth needed. This is important going forward for 4K@144Hz displays, as DP1.4 itself doesn’t provide enough bandwidth for them (leading to other workarounds such as NVIDIA’s 4:2:2 chroma subsampling on G-Sync HDR monitors). This is a feature we’ve talked off and on about for a while, and it’s taken some time for the tech to really get standardized and brought to a point where it’s viable in a consumer product.

AMD Announces Radeon RX 5700 XT & RX 5700 Addendum: AMD Slide Decks
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  • Korguz - Thursday, June 13, 2019 - link

    if navi supported ray tracing.. was just as slow at it as turing, on par with a 2080 in everything else and still $100 cheaper.. most of those that are ridiculing amd now... would probably still be ridiculing them ..
  • Korguz - Monday, June 10, 2019 - link

    BenSkywalker these cards arent even out yet.. wait to see where the prices fall when they are released, then see....
  • BenSkywalker - Monday, June 10, 2019 - link

    You think AMD stated prices to make AMD look bad? I'm honestly confused by your statement, or are you saying after enough backlash they'll be forced to lower prices? Or that if/when the 'super' green parts come out they'll lower the price, before they launch?
  • Korguz - Tuesday, June 11, 2019 - link

    nope.. announced prices.. may not be release prices... they could go up.. or down... just ahve to wait and see
  • CiccioB - Tuesday, June 11, 2019 - link

    If prices go up it is bad for us, if they go down it means that AMD product is not the value they wanted to sell it at and thus having a cut to their margins (as they did since GCN encountered Kepler).
    Sorry, but there's nothing to wait to see if it evolving to a better or worse situation.
    The MSRP are those announced and they have to be compared to the ones of the competition with the same performance.
  • Phynaz - Tuesday, June 11, 2019 - link

    Exactly, these bring nothing new. This is AMD fleecing their fans, and their fans are too dumb to notice.
  • sor - Tuesday, June 11, 2019 - link

    Dude, you need to chill. I’m not even in this fight, I can’t remember the last dedicated video card I bought, but you don’t have to hop on every comment chain and say the same crap.

    This is a mid range card. Of course it’s going to be similar performance to the best card from previous gen. It’s how the product cycles work.

    I’m so out of it that I had to go look up the pricing on RTX 2070. Looks to be $549 on high end and $499 on low. If this new card is a “few percent” better and priced at $449 it seems reasonable, objectively. The price difference could reflect the feature disparity people are alluding to.
  • Korguz - Tuesday, June 11, 2019 - link

    oh like nvidia has done over the last few years with the pricing of their own cards ? come on, unless you have more money then brains.. do you like the prices of nvidia's cards?? i know a few people who hate what nvidia charges for their cards, THAT is the rip off ....
  • wr3zzz - Monday, June 10, 2019 - link

    Is it just me or that starting from last year the price-performance progression has been linear?
  • awehring - Monday, June 10, 2019 - link

    7nm is a quite impressive technology. 251mm2 with 10.3 billion transistors.
    Let's put this into perspective. Take a normal hair (0.05 mm thick), cut it. At the cutting surface you would have about 80'000 transistors.

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