From e2b88612e5c8dfc3f4bf416dff7b1af3e1e4f0f6 Mon Sep 17 00:00:00 2001 From: Vlad Zahorodnii Date: Sun, 27 Jul 2025 15:58:31 +0300 Subject: [PATCH] XCB: Remove extra xcb_randr_select_input() calls This fixes high CPU usage in kwin. If there is a ConfigureNotify event for the root window, QtXCB will call xcb_randr_select_input(). The problem is that the X server may send an output change event in response to xcb_randr_select_input(). When kwin sees that output change event, it will process the event and it can update its override redirect windows, which can produce a few ConfigureNotify events for the root window and make kwin get stuck in an update loop. Since the QXcbConnection constructor already subscribes to the RandR events, these xcb_randr_select_input() function calls can be removed. Also, `true` is not a valid argument for xcb_randr_select_input(). It expects a mask of events to listen. For what it's worth, `true` corresponds to XCB_RANDR_NOTIFY_MASK_SCREEN_CHANGE = 1, which xrandrSelectEvents() already subscribes to. Pick-to: 6.10 6.9 6.8 Change-Id: I950a0a6e2e34822ac3da8cd69b96670e4bf4b07d Reviewed-by: Liang Qi --- diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp index 2f00615..c1b8f84 100644 --- a/src/plugins/platforms/xcb/qxcbscreen.cpp +++ b/src/plugins/platforms/xcb/qxcbscreen.cpp @@ -499,7 +499,6 @@ , m_cursor(std::make_unique(connection, this)) { if (connection->isAtLeastXRandR12()) { - xcb_randr_select_input(xcb_connection(), screen()->root, true); auto crtc = Q_XCB_REPLY_UNCHECKED(xcb_randr_get_crtc_info, xcb_connection(), m_crtc, output ? output->timestamp : 0); if (crtc) { @@ -605,8 +604,6 @@ return; } - xcb_randr_select_input(xcb_connection(), screen()->root, true); - m_monitor = monitorInfo; qCDebug(lcQpaScreen) << "xcb_randr_monitor_info_t: primary=" << m_monitor->primary << ", x=" << m_monitor->x << ", y=" << m_monitor->y << ", width=" << m_monitor->width << ", height=" << m_monitor->height