Intel framebuffer compression & tiling update
Jesse Barnes
jbarnes at virtuousgeek.org
Thu Aug 16 12:15:25 PDT 2007
We've made some recent changes in the Intel git tree, enabling both
tiled rendering for the front buffer by default, and framebuffer
compression by default where available (currently, framebuffer
compression is only available on mobile devices, e.g. 915GM, 965GM).
Tiled frontbuffer rendering should bring us some modest performance
increases for certain operations (render acceleration specifically)
though I haven't done any measurements on it.
Framebuffer compression is an Intel feature that uses run length
encoding (RLE) to compress the front buffer to a separate compressed
buffer from which actual scanout occurs. When enabled, if your desktop
is amenable to RLE, it can save as much as 0.7W in configurations I've
tested, due to reduced memory bandwidth consumption during scanout
(i.e. reading a compressed scanout buffer uses less bw than reading the
full, uncompressed one). It shouldn't measurably affect performance
adversely, since we've configured it to re-compress the front buffer
only every 1000 vblank events, nor should it increase power consumption
in any measurable way, even in pathological configurations.
As usual, please report any bugs related to the above or any other Intel
issue to freedesktop.org bugzilla, ideally after testing with the
latest bits from git.
Thanks,
Jesse
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