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Use a vblank timer to simulate the vblank interrupt. The DRM vblank helpers provide an implementation on top of Linux' hrtimer. Virtgpu enables and disables the timer as part of the CRTC. The atomic_flush callback sets up the event. Like vblank interrupts, the vblank timer fires at the rate of the display refresh. Most userspace limits its page flip rate according to the DRM vblank event. Virtgpu's virtual hardware does not provide vblank interrupts, so DRM sends each event ASAP. With the fast access times of virtual display memory, the event rate is much higher than the display mode's refresh rate; creating the next page flip almost immediately. This leads to excessive CPU overhead from even small display updates, such as moving the mouse pointer. This problem affects virtgpu and all other virtual displays. See [1] for a discussion in the context of hypervdrm. Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Link: https://lore.kernel.org/dri-devel/SN6PR02MB415702B00D6D52B0EE962C98D46CA@SN6PR02MB4157.namprd02.prod.outlook.com/ # [1] Acked-by: Gerd Hoffmann <kraxel@redhat.com> Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Link: https://lore.kernel.org/r/20251008130701.246988-1-tzimmermann@suse.de
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.