GPUOpen On Reducing Vulkan Overhead With Volk, Possible 1~5% Savings
Written by Michael Larabel in Vulkan on 26 April 2018 at 02:05 PM EDT. 19 Comments
A guest post on AMD's GPUOpen blog outlines the overhead issues with using the Vulkan loader library and possible performance advantages to using vkGetDeviceProcAddr or more easily via a little heard of project called Volk.

While the generic Vulkan loader library is great for allowing multiple Vulkan ICD drivers to happily co-exist on the same system without interference and allowing for features like Vulkan layers, it does add a bit of overhead whenever making any Vulkan API calls that need to go through it and in turn passed onto the drivers. Since the Vulkan debut we've seen differing opinions about whether its performance negligible or not from driver developers to Vulkan game/application developers with some app/game developers trying to avoid the loader/dispatch code and use the Vulkan driver calls directly.

Arseny Kapoulkine of Roblox wrote a guest post on the GPUOpen blog today about reducing the Vulkan API call overhead. The most common approach to now for lowering that Vulkan API overhead of going through the loader library is by using vkGetDeviceProcAddr for obtaining a function pointer to what's doing the actual work and thereby bypassing the dispatch work on subsequent calls.

What Arseny Kapoulkine has been working on is the Volk project as an MIT-licensed Vulkan meta-loder. By including the C file with your Vulkan project and including its Volk header file as a replacement to vulkan.h along with other slight changes to the code, it allows for dynamically loading entry-points to use Vulkan without having to link against the common Vulkan loader and using the entry-points directly from the driver.

You can read more about the Vulkan API call overhead on or visit the Volk GitHub site if you are potentially interested in the code.

As far as the advantages, Kapoulkine attributes the normal Vulkan overhead at "1-5% for typical Vulkan applications."
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