Frame buffer access performance

[Daniel Vetter]

On Fri, Aug 05, 2016 at 11:04:21AM +0200, Enrico Weigelt, metux IT consult wrote:
> On 05.08.2016 10:15, Daniel Vetter wrote:
> 
> Hi,
> 
> > There's a driver cap DRM_CAP_DUMB_PREFER_SHADOW for this. If set,
> > render into a shadow buffer and copy over in bursts, otherwise you
> > can assume that the memory is fully cpu cached and fast with random
> > access.
> 
> aaaah!
> 
> nekrad at orion:~/src/linux$ git grep prefer_shadow drivers/gpu/drm/i915
> drivers/gpu/drm/i915/intel_display.c:   dev->mode_config.prefer_shadow = 1;
> 
> IOW: i915 driver (my notebook here has an i915) sets that flag, so
> it seems my guess is right.
> 
> Do we already have some suitable double-buffer helpers, which can detect
> changed regions and copy over in bursts, so userland doesn't
> need extra logic for that ? (hmm, maybe some cow + pagefault magic?)
> 
> ... seems I need to give it some further thoughts ...

DIRTY_FB ioctl. But that's for other manual uplaod displays and similar
things.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch