On Wed, Sep 4, 2019 at 1:56 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: > > (was: drm/vram-helper: Fix performance regression in fbdev) > > Generic fbdev emulation maps and unmaps the console BO for updating it's > content from the shadow buffer. If this involves an actual mapping > operation (instead of reusing an existing mapping), lots of debug messages > may be printed, such as > > x86/PAT: Overlap at 0xd0000000-0xd1000000 > x86/PAT: reserve_memtype added [mem 0xd0000000-0xd02fffff], track write-combining, req write-combining, ret write-combining > x86/PAT: free_memtype request [mem 0xd0000000-0xd02fffff] > > as reported at [1]. Drivers using VRAM helpers may also see reduced > performance as the mapping operations can create overhead. > > 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 avoid the > frequent mappings in the fbdev code. The drivers, ast and mgag200, > map 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 strategy. > > [1] https://lists.freedesktop.org/archives/dri-devel/2019-September/234308.html As discussed on irc a bit, here's my thoughts: - imo we should fix this by using the io_mapping stuff, that avoids the overhead of repeated pat checks for map/unmap. It should also cut down on remapping costs a lot in general (at least on 64bit kernels, which is like everything nowadays). But it's a lot more work to roll out I guess. I think this would be the much better longterm fix. - this here only works when fbcon is active, the noise will come back when you start X or wayland. We should probably check whether the display is active with drm_master_internal_acquire (and reupload when we restore the entire console in the restore function - could just launch the worker for that). I'm also not sure whether we have a real problem here, it's just debug noise that we're fighting here? -Daniel > > v2: > * fixed comment typos > > Thomas Zimmermann (3): > drm/vram: 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 | 19 +++++++ > drivers/gpu/drm/drm_gem_vram_helper.c | 74 +++++++++++++++++++------- > drivers/gpu/drm/mgag200/mgag200_mode.c | 20 +++++++ > include/drm/drm_gem_vram_helper.h | 19 +++++++ > 4 files changed, 114 insertions(+), 18 deletions(-) > > -- > 2.23.0 > -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
