[Bug 57442] New: Several applications: abnormal input delay with Wine

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=57442

Bug ID: 57442
           Summary: Several applications: abnormal input delay with Wine
           Product: Wine
           Version: 9.21
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: win32u
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

I've noticed a slight input delay in one Unreal Engine sample and decided to
test things with my custom application (very simple C++ program that uses SDL2
to poll mouse events and log them). I built this application on Linux with g++,
and cross-compiled it for Windows with mingW. Native Linux built has around
1.05 ms input delay, while Windows build with Wine 9.21 has 9.5 ms input lag. I
believe you can build any application that polls events and test it for
yourself, as I observed the same input lag in Unreal Engine samples (though not
so severe, it's bounded by the Game Thread time)

The way I tested things is a bit complicated, but it's necessary for my goal: I
used Sunshine as a server and Moonlight as a client, and logged when Sunshine
receives the input from Moonlight. We can think of it as kernel receiving
events since Sunshine creates virtual device and sends input there. Then I
logged when application receives the event.

I checked the source code, and I believe the new throttling mechanism
introduced in 9.13 version for input is the reason why it's so slow. If you
re-implement the previous mechanism based on message count, input delay is
almost 0. I wonder if CPU usage would spike though in real games.