[Bug 96743] [BYT, HSW, SKL, BXT, KBL] GPU hangs with GfxBench 4.0 CarChase

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96743

--- Comment #55 from Topi Pohjolainen <topi.pohjolainen at intel.com> ---
The hangs with IVB and HSW are really troublesome to debug. With my own IVB the
reproducibility of the bug changes a lot - sometimes I get it with a few rounds
and sometimes it runs 20 rounds without a hang. This makes it very difficult to
try things out as one can't tell for certain if something has an effect - how
many rounds are really needed to tel for certain?

For this reason I started using one of the machines in the lab - lab_hsw_plex.
With that I couldn't get a hang simply by reverting the two compiler
optimizations discussed earlier. Going back in the commit history until the
introduction of the older of the two optimizations gave me a hang - after some
15 rounds. But since then I haven't been able to get it any more. Moreover, the
signature of the hang pointed to depth clear which is different than before.
Hence I'm guessing I just hit another bug for which I missed the fix while I
moved too far back in the history.

All in all this starts to look like a futile effort considering that none of
the hangs, either on gen7 or later can't be reproduced with current upstream.
I'm going to give one more day for this exercise before my holidays. If nothing
comes out of it, I think we should probably close this.

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