Frame buffer access performance

[Enrico Weigelt, metux IT consult]

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 ...


--mtx