Rex Dieter
6 years ago
parent
c22c09b2de
commit
a54ca5a1c1
@ -0,0 +1,81 @@
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From 0124b1ef191fcafe0d0f89287be66b36833586e6 Mon Sep 17 00:00:00 2001
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From: Erik Kurzinger <ekurzinger@nvidia.com>
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Date: Wed, 19 Jun 2019 07:56:42 -0700
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Subject: [PATCH] [platforms/X11] Disable VSync for QtQuick Windows
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Summary:
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QtQuick windows created by KWin currently use the default swap interval
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of 1, meaning buffer swaps will block until vblank. However, this
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results in a problematic interaction on hybrid graphics systems running
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the proprietary NVIDIA driver. VSync on such setups relies on a system
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called "PRIME synchronization", where the xf86-video-modesetting driver
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controlling the display will signal the NVIDIA driver when vblank has
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occurred. The issue is that it will only do so if there has been damage
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to the screen.
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So, when KWin creates a QtQuick window, compositing will stop waiting on
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the window to render, therefore no damage to the screen will occur. But
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this means that no vblank notifications will be delivered to the NVIDIA
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driver, so the glXSwapBuffers call by the QtQuick window will block
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perpetually. The end result is a freeze of the desktop.
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To get around this, we can simply disable vsync for QtQuick windows by
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setting the swap interval for the default QSurfaceFormat to 0. Since
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they are redirected, this shouldn't cause any tearing.
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BUG: 406180
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FIXED-IN: 5.16.2
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Test Plan:
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Using the proprietary NVIDIA driver on a hybrid graphics system, with
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PRIME synchronization enabled (see
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https://devtalk.nvidia.com/default/topic/957814/linux/prime-and-prime-synchronization/),
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perform any action causing a QtQuick window to be created by KWin, for
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example, triggering the application switcher dialogue with alt + tab.
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Ensure the desktop does not temporarily freeze.
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Note, this required a Qt build that includes commit
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https://code.qt.io/cgit/qt/qtbase.git/commit/?id=0c1831178540462da31fd7a4b6d2e446bc84498b
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resolving a bug that prevented the changing the swap interval.
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Reviewers: #kwin, davidedmundson, zzag
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Reviewed By: #kwin, davidedmundson, zzag
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Subscribers: zzag, romangg, alexeymin, kwin
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Tags: #kwin
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Differential Revision: https://phabricator.kde.org/D21808
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---
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main_x11.cpp | 6 ++++++
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1 file changed, 6 insertions(+)
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diff --git a/main_x11.cpp b/main_x11.cpp
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index c83b8240b..1219337b6 100644
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--- a/main_x11.cpp
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+++ b/main_x11.cpp
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@@ -43,6 +43,7 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
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#include <QFile>
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#include <QLabel>
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#include <QPushButton>
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+#include <QSurfaceFormat>
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#include <QVBoxLayout>
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#include <QX11Info>
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@@ -417,6 +418,11 @@ KWIN_EXPORT int kdemain(int argc, char * argv[])
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KWin::Application::createAboutData();
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KQuickAddons::QtQuickSettings::init();
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+ // disables vsync for any QtQuick windows we create (BUG 406180)
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+ QSurfaceFormat format = QSurfaceFormat::defaultFormat();
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+ format.setSwapInterval(0);
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+ QSurfaceFormat::setDefaultFormat(format);
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+
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QCommandLineOption replaceOption(QStringLiteral("replace"), i18n("Replace already-running ICCCM2.0-compliant window manager"));
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QCommandLineParser parser;
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--
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2.21.0
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