Our previous graphics-card tests have shown that Doom's Vulkan renderer doesn't provide the best performance with GeForces, but we figured we might as well give both of the game's APIs a try to see whether the switch had a meaningful impact on performance from these CPUs. Aside from the switch to Vulkan, we left all of the game's quality settings the same for this test.
Although we haven't seen the best performance from Doom's Vulkan renderer on GeForce cards in the past, making the switch here has a surprising effect on both average frame rates and the 99th-percentile frame time the GTX 1080 can produce. Every CPU here gets a frame-rate increase of some sort, and 99th-percentile frame times fall across the board. The FX-8370 gets the biggest boost of all.
In our measures of "badness," each CPU allows the GTX 1080 to spend an imperceptible amount of time past 16.7 ms working on tough frames. The real improvement comes past the 8.3-ms threshold, where most of the Intel CPUs let the GTX 1080 spend about a tenth of a second on challenging scenes. The Core i7-2600K causes the GTX 1080 to spend about two-tenths of a second on tougher frames—still impressive.
The "most improved" award in these metrics goes to the FX-8370. The Piledriver chip lets the GTX 1080 spend just 1.2 seconds on tough frames with Vulkan running the show, a factor-of-10 improvement over its OpenGL performance. Still, the FX-8370 can't quite match the Intel parts for absolute smoothness.
Doom's performance with Vulkan and these CPUs is fascinating. Although average frame rates under Vulkan drop a bit for all the chips we tested, 99th-percentile frame times improve across the board. Most strikingly, those 99th-percentile figures are more or less equal regardless of the age of the chip in question. We've seen hints of this equalizing effect with Vulkan in informal testing before, but this is the first time we've formally quantified it.
Not every game has a Vulkan rendering path, to be certain, but Doom's implementation suggests that clever developers can extract substantial amounts of performance from older CPUs with the new API. That fact could have important implications for folks with older systems if Vulkan becomes more popular in future titles. For now, though, these results are more of an outlier than the norm.