[Intel-gfx] Missed IRQs on IVB while running intel_gpu_top

[Joe Bloggsian]

Hi, I have an app that uses the IVB bitstream hardware (via
libva/intel-driver), and I have noticed some reported missed bsd IRQs
in dmesg.  After some testing I believe this only occurs when I run
intel_gpu_top, so I'm assuming this is an issue with intel_gpu_top
rather than the resolved bug 38862.

I can reproduce the issue quickly by running intel_gpu_top at the same
time as 8 instances of gem_dummy_reloc_loop on a loop (one instance is
enough, but takes longer!).  I only see missed bsd/blt ring IRQs, not
render.  I haven't seen any missed IRQs in the same test without
intel_gpu_top.

Of course a workaround is to only use intel_gpu_top while developing,
and not on production devices since it's really a test tool, but it
would be good to understand and it's definitely useful to know GPU
load for real - as an aside, it's great that Intel releases such
tools/source/documentation.

Does anyone know whether this is expected behavior and/or how to fix it please?

I am using a core i7 3612QE/HD4000 with a 3.5.0 kernel, libdrm 2.4.39
(Ubuntu 12.10 x64) and intel_gpu_top/gem_dummy_reloc_loop built from
the very recent commit 3149531 of intel-gpu-tools.

Thanks,
Joe.