Raspberry Pi 4 - Forced VSYNC?!

FranceMSR

Hi all, I wrote a porting of M.A.M.E. with the scope of great performance also on Raspberry Pi v1. I'm using SDL2 for the interface with the operating system.

It works fine but with Raspberry Pi 4 there is a problem. It runs slower than Raspberry Pi 3.

During my investigation I removed from my code the part that is responsible of adaptive dynamic frameskipping, audio/video synchronization and nominal FPS targeting. In this way the application must be run as fast as it can.

In this way games run faster, 200 FPS on my laptop, a little slower on Raspberry Pi 3 (but over 100 FPS)... On Raspberry Pi 4 it runs at 60 FPS like an hardware (or software, maybe driver?!?!) performs a VSYNC.

I can't find a solution, have you any ideas? Is there a way to run glxgears closing EmulationStation?

RetroPie v4.7.1, fresh install

mitu

I remember being a SDL2 issue with its KMS video driver.
RetroPie ships with 2.0.10, you may try with a newer SDL version (though they may have some quirks with the KMS video driver, that's why they're not yet included).

FranceMSR

Hi @mitu, thanks for reply.

I don't understand the point because if there is a bug on SDL 2.0.10 the same behaviour should happens with Raspberry Pi v3. So there is a difference between Raspberry Pi v3 and Raspberry Pi v4 that creates the problem. Video driver? Hardware?

Anyway I tried with RetroPie 4.7.1 stock (5.4 kernel) and after a full upgrade (so new kernel). After that I changed this option in config.txt

dtoverlay=vc4-fkms-v3d

so, as I understand, Fake KMS in this

dtoverlay=vc4-kms-v3d

so Full KMS. The problem persists. I will try to use newer SDL version in order to continue my investigation.

Maybe there is a wrong interaction between KMS and SDL2 that only appears on Raspberry Pi v4

mitu

@francemsr said in Raspberry Pi 4 - Forced VSYNC?!:

I don't understand the point because if there is a bug on SDL 2.0.10 the same behaviour should happens with Raspberry Pi v3. So there is a difference between Raspberry Pi v3 and Raspberry Pi v4 that creates the problem. Video driver? Hardware?

The Pi3 (and previous models) has a different video driver in SDL2 - as I said the issue is with the KMS video driver (which is used on the Pi4).

FranceMSR

@mitu sorry but you wrote "I remember being a SDL2 issue with its KMS video driver." as kind of sort of SDL-ONLY-RELATED internal driver, not Raspberry Pi one :-)

As I said before, I'll try SDL 2.0.14 and I'll report the result

mitu

@francemsr Yes, it's the SDL2 driver, not the Linux kernel or Mesa drivers.

FranceMSR

@mitu good, thanks.

Just for testing purpose: is there a way to use glxgears closing EmulationStation?

mitu

@francemsr You can install the desktop part as a Port and start it from EmulationStation - https://retropie.org.uk/docs/FAQ/#where-did-the-desktop-go

FranceMSR

@mitu ok, I thought there was a different way instead of pass from Desktop Environment.

Thanks for now

mitu

@francemsr You can instruct the RetroPie launcher (runcommand) to start an emulator/program via xorg by adding XINIT to its command in emulators.cfg - for instance this is how steamlink is started (see here).

FranceMSR

@mitu oh good thing!

FranceMSR

Built SDL2 with --enable-video-kmsdrm parameter, this is the result of pre-build configuration

SDL2 Configure Summary:
Building Shared Libraries
Building Static Libraries
Enabled modules : atomic audio video render events joystick haptic sensor power filesystem threads timers file loadso cpuinfo assembly
Assembly Math   :
Audio drivers   : disk dummy oss alsa(dynamic) sndio(dynamic)
Video drivers   : dummy rpi x11(dynamic) kmsdrm(dynamic) opengl opengl_es1 opengl_es2 vulkan
X11 libraries   : xcursor xdbe xinerama xinput2 xinput2_multitouch xrandr xscrnsaver xshape xvidmode
Input drivers   : linuxev linuxkd
Enable virtual joystick APIs : YES
Using libsamplerate : YES
Using libudev       : YES
Using dbus          : YES
Using ime           : YES
Using ibus          : YES
Using fcitx         : YES

When Raspberry Pi starts EmulationStation crashes on Creating window... log. Maybe I break something, any idea? This happens both with dtoverlay=vc4-fkms-v3d and dtoverlay=vc4-kms-v3d

P.S.: Building without --enable-video-kmsdrm option bring me to console with error related on creation of OpenGL window

mitu

Try to disable the rpi video driver when configuring SDL2.

FranceMSR

@mitu Built SDL 2.0.14 with

--disable-video-rpi --enable-video-kmsdrm

The FPS problem still exists with 5.4 kernel, or newer one after full SO upgrade (in this case with fkms or kms), and in this way when emulator is closed EmulationStation is frozen.

Anyway I found a solution, if VERTICAL SYNC is enabled also on emulator (I added a command line parameter for this) also Raspberry Pi v4 version is ok.

If you don't have any other idea I'll stop the investigation, I don't love VSYNC because if a user has a 50 Hz monitor all games with nominal 60 FPS framerate runs at 50 FPS.

Really appreciate your help