backend: glx: tentatively enable glFinish for NVIDIA

We use the __GL_YIELD=usleep workaround when we detect the NVIDIA
driver, so we could use glFinish without the NVIDIA driver taking all
the CPU.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/driver.c

@@ -12,6 +12,13 @@
 #include "compiler.h"
 #include "log.h"
 
+/// Apply driver specified global workarounds. It's safe to call this multiple times.
+void apply_driver_workarounds(enum driver driver) {
+	if (driver & DRIVER_NVIDIA) {
+		setenv("__GL_YIELD", "usleep", true);
+	}
+}
+
 enum driver detect_driver(xcb_connection_t *c, backend_t *backend_data, xcb_window_t window) {
 	enum driver ret = 0;
 	// First we try doing backend agnostic detection using RANDR

src/backend/driver.h

@@ -32,6 +32,9 @@ enum driver {
 /// Note, this is a best-effort test, so no guarantee all drivers will be detected.
 enum driver detect_driver(xcb_connection_t *, struct backend_base *, xcb_window_t);
 
+/// Apply driver specified global workarounds. It's safe to call this multiple times.
+void apply_driver_workarounds(enum driver);
+
 // Print driver names to stdout, for diagnostics
 static inline void print_drivers(enum driver drivers) {
 	if (drivers & DRIVER_AMDGPU) {

src/backend/gl/glx.c

@@ -466,11 +466,8 @@ static void glx_present(backend_t *base, const region_t *region attr_unused) {
 	struct _glx_data *gd = (void *)base;
 	gl_present(base, region);
 	glXSwapBuffers(gd->display, gd->target_win);
-	// XXX there should be no need to block, the core should wait for render to finish
-	if (!gd->gl.is_nvidia) {
 	glFinish();
 }
-}
 
 static int glx_buffer_age(backend_t *base) {
 	if (!glxext.has_GLX_EXT_buffer_age) {

src/picom.c

@@ -1224,6 +1224,7 @@ static bool redirect_start(session_t *ps) {
 
 	// Re-detect driver since we now have a backend
 	ps->drivers = detect_driver(ps->c, ps->backend_data, ps->root);
+	apply_driver_workarounds(ps->drivers);
 
 	root_damaged(ps);
 
@@ -1965,6 +1966,7 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 	// window; non experimental backends always need a target window
 
 	ps->drivers = detect_driver(ps->c, ps->backend_data, ps->root);
+	apply_driver_workarounds(ps->drivers);
 
 	// Initialize filters, must be preceded by OpenGL context creation
 	if (!ps->o.experimental_backends && !init_render(ps)) {