A beefier GPU based on a better GCN
The Radeon graphics units in this new APU are based on the third generation of the GCN architecture, and they're most closely related to the discrete Tonga GPU that powers the Radeon R9 285. The core graphics technology isn't terribly different from what AMD first shipped aboard the Radeon HD 7000 series, but the firm has made some incremental improvements over time in areas like tessellation performance.
Carrizo inherits the delta-based color compression scheme first used in Tonga. This logic conserves memory bandwidth by storing color data in a losslessly compressed format. AMD claims this feature alone can improve performance in games by five to seven percent at the cost of a "modest" amount of additional silicon area.
This SoC's graphics block consists of eight GCN compute units tied to two render back-ends and 512KB of dedicated L2 cache for graphics. All told, that amounts to 512 stream processors, 32 texels per clock of texture filtering capacity, and eight pixels per clock of ROP throughput. AMD cites a peak arithmetic rate of 819 gigaflops, presumably for the fastest 35W model of Carrizo.
Notably, the graphics portion of Carrizo occupies its own separate voltage plane on the chip. Thus, it can operate more efficiently by selecting the optimal voltage for its own needs. As a result, this chip can squeeze into smaller power envelopes while keeping all eight of its GCN compute units active. Those units can run at higher peak frequencies, as well.
These changes add up to concrete gains in performance over the prior generation, again especially in the 15W power envelope.
AMD bills Carrizo as the first HSA 1.0 compliant APU, a claim that may seem strange to those familiar with HSA, since AMD has been talking about it for years. However, the 1.0 spec is a new thing, and Kaveri didn't implement a few features needed to meet its requirements, such as GPU-based context-switching. Carrizo adds that capability and thus earns its billing.
This APU's support for HSA should position it as an obvious development platform for HSA-based applications, but I don't believe Carrizo has the necessary plumbing to deliver on HSA's performance promises. We'll likely have to wait another generation or two, until APUs get a cache-coherent common interconnect fabric and shared last-level caching, before the hardware is ready to match AMD's vision.
Better video processing hardware
The UVD block on AMD's chips hosts dedicated logic meant to accelerate the encoding and decoding of popular video compression formats. Carrizo's UVD unit looks to be the very latest revision of AMD's technology in this space. It adds the ability to decode the HEVC/H.265 format expected to be widely used for streaming in the future, especially for 4K content.
AMD has quadrupled the throughput of the UVD block, too, in order to support 4K video properly. The firm demonstrated flawless 4K video playback with low CPU utilization back at CES in January on early Carrizo silicon. This is one area where Carrizo's feature set clearly trumps that of Intel's Broadwell. For 1080p video playback, the APU is now able to spend about 25% of its time doing the actual decode work and the rest dropping into a power-gated sleep state, saving energy.
Another video-focused enhancement in this SoC is the addition of a dedicated, high-quality image scaling unit in the display pipeline. Older AMD APUs have used the GPU's shader units to scale images to fit the target display's resolution, but doing so burns power. By switching to custom scaler hardware, the firm reckons it saves about half a watt compared to GPU-based scaling.
All in all, AMD estimates that Carrizo cuts power consumption during 1080p video playback roughly in half, taking it down under five watts.
Here is a terrifying slide from the AMD presentation that shows older APUs lasting only 3.3 hours while playing 1080p videos on a 50Whr battery. I'm not sure what to make of that.
A bit of the performance picture
AMD's presentations are rife with performance results from various scenarios, but I'm naturally skeptical of performance claims in the absence of actual hardware to test—and AMD tells us we won't likely see that until perhaps July. I'll offer a couple of slides, though, in order to give you a sense of what the firm expects users to see from Carrizo-equipped laptops.
Yes, it can play DOTA 2 and LoL. And yes, it's faster than Haswell-based Core i5 and i7 processors (at least in 3DMark).
I think the question on everyone's minds is whether it's faster than Intel's just-introduced Broadwell Core i5/i7 processors. Although AMD has traditionally led the market in integrated graphics performance, those Broadwell chips look to be pretty formidable, thanks in part of 128MB of eDRAM serving as a graphics cache. Then again, the Iris Pro Broadwell processors have 47W power envelopes, above the 35W peak for the first round of Carrizo parts.
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