In SDL 2.0.10, SDL_WaitEvent() can stall for a short but noticeable period of time (200-300ms?) even while events are pending.  I observed this as seeing joystick input seem to drop out once every few seconds using a udev-based controller (specifically a Sony DualShock 3).

This does not occur in SDL 2.0.9.

Sample code (spin an analog stick and watch for the event counter to pause):
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#include <assert.h>
#include <stdio.h>
#include <SDL2/SDL.h>
int main(void)
{
    int counter = 0;
    SDL_Init(SDL_INIT_EVERYTHING);
    assert(SDL_NumJoysticks() >= 1);
    SDL_Joystick *js = SDL_JoystickOpen(0);
    assert(js);
    for (;;) {
        SDL_Event event;
        SDL_WaitEvent(&event);
        printf("event %d\n", counter++);
    }
}
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