[Bug 61152] Ubuntu12.04.2 LinearFramebuffer under extended mode broken by intel_gen4_compute_offset_xtiled()

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=61152

--- Comment #18 from Chris Wilson <chris at chris-wilson.co.uk> ---
Yes, the minimum access pattern of the render pipeline is a 2x2, and if the
stride is such that cross a page boundary, you incur a TLB miss on every pixel.

The BLT engine doesn't have the same access pattern and so is not as adversely
affected.

For the operations you want to perform the render pipeline is typically much
faster (as that uses the L3 cache, which even has a notable impact for simple
copies). Conversely the BLT has lower latency...

Forcing a LinearFramebuffer is a hack. Using a linear intermediate is still a
hack, but at least a step forward.

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