The 805 Extends Snapdragon’s Performance Advantage
Snapdragon 805 turns out to be much more interesting than the 801, which we tested in Qualcomm Snapdragon 801: Performance Previewed. While Snapdragon 801 was a mere clock rate bump over the 800 and didn't offer any architectural changes, Snapdragon 805 introduces us to Qualcomm's next-generation Adreno GPU.
The Adreno 420 sees improvements along the entire length of the rendering pipeline, from an improved z-buffer to tuned ROPs. Qualcomm won't say for sure, but there are likely additional TMUs fed by copious amounts of memory bandwidth, and larger texture and L2 caches. All of those improvements lead to impressive performance gains over the Adreno 330 in Snapdragon 800/801, placing the 805 firmly ahead of the PowerVR G6430.
While Adreno 420’s benchmark performance is impressive, does it push the envelope far enough to outperform the PowerVR Series6XT GPU due to arrive later this year? And, equally important, does it compete with Nvidia’s Kepler-powered Tegra K1? If initial performance figures from Nvidia are to be believed, the Adreno 420’s benchmark dominance may be short-lived.
We'll have to wait until 2015 and Snapdragon 810 to see any significant changes to the CPU complex. For now, Krait 450's tuned circuit layer delivers a higher maximum frequency, at least on paper. While our single-core CPU benchmarks confirm performance gains commensurate with a clock rate increase, Snapdragon 805 struggles to achieve its peak frequency with all four cores active. We can’t blame thermal throttling, since the 805 we tested was housed in a large tablet with a cool-running chassis. Also, we spread the benchmarks over several of these reference platforms, which helped keep heat build-up at bay. Keep in mind though that these were development tablets, not shipping units. So, Qualcomm’s software stack may not be fully optimized, or perhaps the company is using a conservative frequency scaling algorithm to keep SoC temperatures under control. This is a topic to revisit once retail devices start shipping.
With the Krait family of CPUs, Qualcomm opted for clock frequency over pipeline width and complexity. This strategy still works, but I don't see it being viable long-term. We’ve already seen a similar strategy fail on the desktop. Remember Intel's Pentium 4? The CPU/SoC either runs into a power/thermal wall or the weakest link in the pipeline becomes a bottleneck that prevents further scaling. Getting more work done in the same amount of time through IPC improvements can have a detrimental impact on power consumption. However, racing to get as much of the SoC back to sleep as possible, along with clever power gating, helps mitigate some of that. I suspect that Snapdragon 810’s new 64-bit architecture will look more like Apple’s Cyclone CPU than Krait.
With its more powerful GPU, Snapdragon 805 seems best suited to high-resolution tablets and smartphones with large screens. Larger form factors also provide more thermal headroom for Krait 450’s higher frequencies. It’s likely we’ll see Snapdragon 801 remain the more popular option for smartphones, while the 805 powers a new generation of tablets.
