Compositors often depend on vblanks to limit their display-update rate. Without, they see vblank events ASAP, which creates high CPU overhead. This is especially a problem with virtual devices with fast framebuffer access.
The series moves vkms' vblank timer to DRM and converts a number of drivers. The final patch rate-limits the output of DRM's framebuffer console to vblank intervals. It has been taken from [1]. It reduces the time for doing time find /usr/src/linux from 24s to 20s with the patched bochs driver. Apparently the system is spending less CPU overhead on display updates. This is an RFC patchset to see if the approach is feasible. It's been motivated by a recent discussion about hypervdrm [2] and other long- standing bug reports. [3][4] [1] https://patchwork.freedesktop.org/series/66442/ [2] https://lore.kernel.org/dri-devel/20250523161522.409504-1-mhkli...@outlook.com/T/#ma2ebb52b60bfb0325879349377738fadcd7cb7ef [3] https://bugzilla.suse.com/show_bug.cgi?id=1189174 [4] https://invent.kde.org/plasma/kwin/-/merge_requests/1229#note_284606 Thomas Zimmermann (6): drm/vblank: Add vblank timer drm/vkms: Use vblank timer drm/simpledrm: Use vblank timer drm/bochs: Use vblank timer drm/hypervdrm: Use vblank timer drm/fb-helper: Synchronize dirty worker with vblank drivers/gpu/drm/Makefile | 3 +- drivers/gpu/drm/drm_fb_helper.c | 20 ++++ drivers/gpu/drm/drm_vblank_timer.c | 100 ++++++++++++++++++++ drivers/gpu/drm/hyperv/hyperv_drm.h | 4 + drivers/gpu/drm/hyperv/hyperv_drm_modeset.c | 70 ++++++++++++++ drivers/gpu/drm/sysfb/simpledrm.c | 81 ++++++++++++++++ drivers/gpu/drm/tiny/bochs.c | 68 +++++++++++++ drivers/gpu/drm/vkms/vkms_crtc.c | 49 +++------- drivers/gpu/drm/vkms/vkms_drv.h | 6 +- include/drm/drm_vblank_timer.h | 26 +++++ 10 files changed, 386 insertions(+), 41 deletions(-) create mode 100644 drivers/gpu/drm/drm_vblank_timer.c create mode 100644 include/drm/drm_vblank_timer.h -- 2.49.0
