WindowServer: Limit msync to 60 Hz and only sync necessary pages

This speeds up GUI a lot. I can now run GUI on real hardware at almost
60 Hz.

userspace/WindowServer/WindowServer.cpp

@@ -11,6 +11,15 @@
 #include <sys/mman.h>
 #include <sys/socket.h>
 
+WindowServer::WindowServer(Framebuffer& framebuffer)
+	: m_framebuffer(framebuffer)
+	, m_cursor({ framebuffer.width / 2, framebuffer.height / 2 })
+	, m_font(MUST(LibFont::Font::load("/usr/share/fonts/lat0-16.psfu"_sv)))
+{
+	MUST(m_pages_to_sync_bitmap.resize(BAN::Math::div_round_up<size_t>(m_framebuffer.width * m_framebuffer.height * sizeof(uint32_t), 4096 * 8), 0));
+	invalidate(m_framebuffer.area());
+}
+
 BAN::ErrorOr<void> WindowServer::set_background_image(BAN::UniqPtr<LibImage::Image> image)
 {
 	if (image->width() != (uint64_t)m_framebuffer.width || image->height() != (uint64_t)m_framebuffer.height)
@@ -350,10 +359,52 @@ void WindowServer::invalidate(Rectangle area)
 		}
 	}
 
-	uintptr_t mmap_start = reinterpret_cast<uintptr_t>(m_framebuffer.mmap) + area.y * m_framebuffer.width * 4;
+	const uintptr_t mmap_start = reinterpret_cast<uintptr_t>(m_framebuffer.mmap) + area.y * m_framebuffer.width * 4;
-	uintptr_t mmap_end = mmap_start + (area.height + 1) * m_framebuffer.width * 4;
+	const uintptr_t mmap_end = mmap_start + (area.height + 1) * m_framebuffer.width * 4;
-	mmap_start &= ~(uintptr_t)0xFFF;
+
-	msync(reinterpret_cast<void*>(mmap_start), mmap_end - mmap_start, MS_SYNC);
+	uintptr_t mmap_addr = mmap_start & ~(uintptr_t)0xFFF;
+	while (mmap_addr < mmap_end)
+	{
+		size_t index = (mmap_addr - reinterpret_cast<uintptr_t>(m_framebuffer.mmap)) / 4096;
+		size_t byte = index / 8;
+		size_t bit  = index % 8;
+		m_pages_to_sync_bitmap[byte] |= 1 << bit;
+		mmap_addr += 4096;
+	}
+}
+
+void WindowServer::sync()
+{
+	size_t synced_pages = 0;
+
+	for (size_t i = 0; i < m_pages_to_sync_bitmap.size() * 8; i++)
+	{
+		size_t byte = i / 8;
+		size_t bit  = i % 8;
+		if (!(m_pages_to_sync_bitmap[byte] & (1 << bit)))
+			continue;
+
+		size_t len = 1;
+		while (i + len < m_pages_to_sync_bitmap.size() * 8)
+		{
+			size_t byte = (i + len) / 8;
+			size_t bit  = (i + len) % 8;
+			if (!(m_pages_to_sync_bitmap[byte] & (1 << bit)))
+				break;
+			len++;
+		}
+
+		msync(
+			reinterpret_cast<uint8_t*>(m_framebuffer.mmap) + i * 4096,
+			len * 4096,
+			MS_SYNC
+		);
+		synced_pages += len;
+
+		i += len;
+	}
+
+	memset(m_pages_to_sync_bitmap.data(), 0, m_pages_to_sync_bitmap.size());
 }
 
 Rectangle WindowServer::cursor_area() const

userspace/WindowServer/WindowServer.h

@@ -19,13 +19,7 @@
 class WindowServer
 {
 public:
-	WindowServer(Framebuffer& framebuffer)
+	WindowServer(Framebuffer& framebuffer);
-		: m_framebuffer(framebuffer)
-		, m_cursor({ framebuffer.width / 2, framebuffer.height / 2 })
-		, m_font(MUST(LibFont::Font::load("/usr/share/fonts/lat0-16.psfu"_sv)))
-	{
-		invalidate(m_framebuffer.area());
-	}
 
 	BAN::ErrorOr<void> set_background_image(BAN::UniqPtr<LibImage::Image>);
 
@@ -38,6 +32,7 @@ public:
 
 	void set_focused_window(BAN::RefPtr<Window> window);
 	void invalidate(Rectangle area);
+	void sync();
 
 	Rectangle cursor_area() const;
 
@@ -53,6 +48,8 @@ private:
 	BAN::Vector<BAN::RefPtr<Window>> m_client_windows;
 	BAN::Vector<int> m_client_fds;
 
+	BAN::Vector<uint8_t> m_pages_to_sync_bitmap;
+
 	BAN::UniqPtr<LibImage::Image> m_background_image;
 
 	bool m_is_mod_key_held { false };

userspace/WindowServer/main.cpp

@@ -181,8 +181,21 @@ int main()
 		if (auto ret = window_server.set_background_image(BAN::move(config.background_image)); ret.is_error())
 			dwarnln("Could not set background image: {}", ret.error());
 
+	constexpr uint64_t sync_interval_us = 1'000'000 / 60;
+	timespec last_sync { .tv_sec = 0, .tv_nsec = 0 };
 	while (!window_server.is_stopped())
 	{
+		timespec current_ts;
+		clock_gettime(CLOCK_MONOTONIC, &current_ts);
+
+		uint64_t us_since_last_sync = (current_ts.tv_sec - last_sync.tv_sec) * 1'000'000 + (current_ts.tv_nsec - last_sync.tv_nsec) / 1000;
+		if (us_since_last_sync > sync_interval_us)
+		{
+			window_server.sync();
+			us_since_last_sync = 0;
+			last_sync = current_ts;
+		}
+
 		int max_fd = server_fd;
 
 		fd_set fds;
@@ -200,7 +213,14 @@ int main()
 		}
 		max_fd = BAN::Math::max(max_fd, window_server.get_client_fds(fds));
 
-		if (select(max_fd + 1, &fds, nullptr, nullptr, nullptr) == -1)
+		timeval select_timeout {
+			.tv_sec = 0,
+			.tv_usec = static_cast<long>(sync_interval_us - us_since_last_sync)
+		};
+		int nselect = select(max_fd + 1, &fds, nullptr, nullptr, &select_timeout);
+		if (nselect == 0)
+			continue;
+		if (nselect == -1)
 		{
 			dwarnln("select: {}", strerror(errno));
 			break;