GPU hung with Linux-3.2-rc6

[Udo Steinberg <udo@hypervisor.org>]

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Hi,

With Linux-3.2-rc6 I'm frequently seeing GPU hangs when large amounts of
text scroll in an xterm, such as when extracting a tar archive. Such as this
one (note the timestamps):

[22865.157750] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[22865.157763] [drm:kick_ring] *ERROR* Kicking stuck semaphore on render ring
[22871.165992] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[22871.166008] [drm:kick_ring] *ERROR* Kicking stuck semaphore on render ring
[22877.417902] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[22877.417915] [drm:kick_ring] *ERROR* Kicking stuck semaphore on render ring
[22883.426132] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[22883.426146] [drm:kick_ring] *ERROR* Kicking stuck semaphore on render ring

These hangs did not occur with Linux 3.1 or they were so infrequent that I
didn't notice them. The machine is an x220 laptop with SNB CPU. The kernel
command line contains:

i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1

Note that VT-d is enabled in the BIOS, but the kernel is compiled without
IOMMU support. Because the IOMMU is not enabled, I'm inclined to think that
this problem is not VT-d related.

Cheers,

	- Udo

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