[Bug 77436] KDE Konsole very slow scrolling with TearFree and QT graphics system native

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=77436

--- Comment #77 from Chris Wilson <chris at chris-wilson.co.uk> ---
I pushed a variant as

commit 1beaa980ea6a9617f7dd4dc87b881c37cc7a277b
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Wed Jun 11 16:41:22 2014 +0100

    sna/gen6+: On small GT avoid the intermediate copy for overlaps

    If the memory bw is constrained on the GPU avoid doing the 2-pass copy
    for overlaps on the render ring, and do the single pass slower BLT copy
    instead - as since it has to transfer less data it will be faster.

    Reported-by: Ildar Nurislamov <absorbb at gmail.com>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77436
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>


If that makes scrolling fluid, great. I'd like to dig more into why it slowed
down so much though. My guess is due to cache thrashing on the GPU and memory
bandwidth, but I don't feel that adequately explains how far behind the GPU got
in the command stream, nor how it interacted with a loaded system.

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