Comment 0 for bug 1585723

I'm digging into unity8 performance problems on older generation Intel GPUs - specifically i915 Atom GPUs.

I've tested a simple QML file with a single empty UbuntuShape in it:

import QtQuick 2.4
import Ubuntu.Components 1.3

Rectangle {
    width: 400
    height: 300
    color: "blue"

    UbuntuShape {}
}

Running it with INTEL_DEBUG=perf env var set, I get this output:

i915_program_error: Exceeded max ALU instructions (76 out of 64)
ENTER FALLBACK 10000: Program
Mapping a busy BO, causing a stall on the GPU.

which implies that MESA was unable to compile one of the UbuntuShape shaders as it created more ALU instructions than the GPU could deal with.

The GPU stall message I guess is related to that.