https://bugs.kde.org/show_bug.cgi?id=406180
Erik Kurzinger <ekurzin...@nvidia.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Latest Commit| |https://commits.kde.org/kwi
| |n/56cd5f5557fbec291a9d44f6f
| |26fb76b5c34adae
Version Fixed In| |5.16.2
Status|CONFIRMED |RESOLVED
--- Comment #82 from Erik Kurzinger <ekurzin...@nvidia.com> ---
Git commit 56cd5f5557fbec291a9d44f6f26fb76b5c34adae by Erik Kurzinger.
Committed on 19/06/2019 at 14:56.
Pushed by ekurzinger into branch 'master'.
[platforms/X11] Disable VSync for QtQuick Windows
Summary:
QtQuick windows created by KWin currently use the default swap interval
of 1, meaning buffer swaps will block until vblank. However, this
results in a problematic interaction on hybrid graphics systems running
the proprietary NVIDIA driver. VSync on such setups relies on a system
called "PRIME synchronization", where the xf86-video-modesetting driver
controlling the display will signal the NVIDIA driver when vblank has
occurred. The issue is that it will only do so if there has been damage
to the screen.
So, when KWin creates a QtQuick window, compositing will stop waiting on
the window to render, therefore no damage to the screen will occur. But
this means that no vblank notifications will be delivered to the NVIDIA
driver, so the glXSwapBuffers call by the QtQuick window will block
perpetually. The end result is a freeze of the desktop.
To get around this, we can simply disable vsync for QtQuick windows by
setting the swap interval for the default QSurfaceFormat to 0. Since
they are redirected, this shouldn't cause any tearing.
FIXED-IN: 5.16.2
Test Plan:
Using the proprietary NVIDIA driver on a hybrid graphics system, with
PRIME synchronization enabled (see
https://devtalk.nvidia.com/default/topic/957814/linux/prime-and-prime-synchronization/),
perform any action causing a QtQuick window to be created by KWin, for
example, triggering the application switcher dialogue with alt + tab.
Ensure the desktop does not temporarily freeze.
Note, this required a Qt build that includes commit
https://code.qt.io/cgit/qt/qtbase.git/commit/?id=0c1831178540462da31fd7a4b6d2e446bc84498b
resolving a bug that prevented the changing the swap interval.
Reviewers: #kwin, davidedmundson, zzag
Reviewed By: #kwin, davidedmundson, zzag
Subscribers: zzag, romangg, alexeymin, kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D21808
M +6 -0 main_x11.cpp
https://commits.kde.org/kwin/56cd5f5557fbec291a9d44f6f26fb76b5c34adae
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