Rewriting Vertex Processing for Massive Performance Gains

Greetings. I am kd-11, graphics developer for rpcs3 with a mid-month update on latest developments on the emulator.

As many are already aware, a lot has been going on lately with the new changes to the RSX (the PS3 GPU) emulation, dubbed vertex rewrite. This change moves a lot of vertex processing duties from the CPU to the GPU where they rightly belong and as a result there are massive performance gains especially with OpenGL but also with Vulkan in geometry heavy scenes.


Most if not all users are probably aware by now, but dedicated graphics cards exist on a physically separate board. This means data has to be moved to and from it through the PCI-E bus which is quite fast. However, while it is high bandwidth, it is also high-latency. That means you cannot just send something over there and expect to get it immediately available for the next draw call. Instead, the GPU has to wait for data to be prepared and then signaled that data is ready for processing before drawing begins. This is a general simplification, but it helps illustrate the point. The RSX on the PS3 doesn’t work the same way however. It has near direct access to the XDR main memory on a PS3 and ‘pulls’ data directly from main memory as though it were local memory. It is somewhat similar to integrated graphics memory in this case. That means data is not ‘pre-packaged’ for transport to the PS3 GPU since the memory is virtually unified from the point of view of the RSX. When using Vulkan, drawing is not scheduled until the whole command queue is flushed mitigating the impact of transfer since data will likely have been uploaded beforehand, but for OpenGL this was a big bottleneck.

The second issue was that the emulator was doing a lot of computation on the CPU on how to read vertex data from main memory, essentially pre-packaging the data into formats easy for GPUs to use. This is a very slow process and also very memory intensive (hence the ‘Working buffer not enough’ crashes). Enabling a debug overlay with the old method shows some games taking up to 200ms to prepare vertex data for one frame (Hellboy: The Science of Evil). This is obviously not optimal. The impact could be lowered by using more threads for vertex processing, but with the number of threads already needed to emulate the PS3’s multi-core processor, it was a problem. Spawning 8+ vertex processing threads reduced the time spent processing vertices, but cost other threads to starve and performance would drop significantly. The solution was to shift the work to the GPU instead and not touch it in any way. Just copy the data block and the GPU could fetch the data it needed for itself, mimicking the behaviour of the real hardware.

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RPCS3 Has Moved to Qt

June has been an exciting month for RPCS3. Quite a few new features have been added to the emulator, with a healthy focus on the somewhat outdated GUI. This post will break down some of changes brought by Qt, as well as new features introduced since the transition. This mini progress report will only focus on GUI changes. The main progress report to be published tomorrow will cover the rest.

First up is, obviously, the actual transition from the user interface toolkit WxWidgets to Qt. This transition has been a long and time consuming process, but it added a host of new functionality, both visible and not so visible. A non-exhaustive list of the transition pull requests, the main of which can be found here is:

  • – Appveyor and Travis now build with Qt project, thanks to hcorion. This switches the nightly builds, and eventually the linux builds, to use the Qt interface.
  • – Made some design changes to the GUI, such as progress bars and taskbars now showing percent completion and slight improvements to the Vulkan/DX12 adapter selection box to make it easier to use.
  • – Added support for layouts, which allows you to move your docked widgets as you please.
  • – Added support for booting games in fullscreen.
  • – Added a Welcome screen to point new users to the Quickstart setup guide.
  • – Support for themes! An example can be found further down.

As with all major changes, this caused a few hiccups, but they are being worked on as they are found, and issues can be reported here.

This transition to Qt brought a wave of GUI improvements with it. First up was a recent games list, implemented in #2843 and #2847. This saves the last nine games launched in an easy to use list that has hotkeys, so that those with large libraries, or those using Blu-ray disc games, can easily launch their favorites. The list can be frozen, though items cannot yet be pinned.

Second was a new viewing mode and a tool bar. The game list can now be viewed as a simple grid:

As you can see in the screenshot provided by user Talkashie(which also shows a custom made theme!), the new toolbar allows for searching of large libraries, as well as directly filtering the list by game types. An example being that you can filter out audio/video apps and home apps, or you can choose to view only HDD games. Thanks to user rutantan for creating the very nice button icons in the toolbar.

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