Generic fbdev emulation maps and unmaps the console BO for updating it's content from the shadow buffer. Drivers using VRAM helpers may see reduced performance as the mapping operations can create significant overhead. A report of this problem is at [1].
This patch set fixes the problem by adding a ref counter to the GEM VRAM buffers' kmap operation, and keeping the fbdev's console buffer mapped while the console is being displayed. These changes avoids the frequent mappings in the fbdev code. The drivers, ast and mgag200, maps the console's buffer when it becomes visible and the fbdev code reuses this mapping. The original fbdev code in ast and mgag200 used the same optimization.
[1] https://lists.freedesktop.org/archives/dri-devel/2019-July/228663.html
Thomas Zimmermann (3): drm/vram-helpers: Add kmap ref-counting to GEM VRAM objects drm/ast: Map fbdev framebuffer while it's being displayed drm/mgag200: Map fbdev framebuffer while it's being displayed
drivers/gpu/drm/ast/ast_mode.c | 20 +++++++ drivers/gpu/drm/drm_gem_vram_helper.c | 74 +++++++++++++++++++------- drivers/gpu/drm/mgag200/mgag200_mode.c | 21 ++++++++ include/drm/drm_gem_vram_helper.h | 13 +++++ 4 files changed, 110 insertions(+), 18 deletions(-)
-- 2.22.0