Chris Wilson <ch...@chris-wilson.co.uk> writes:

> Quoting Chris Wilson (2018-05-11 13:11:47)
>> The original switch to use CSB from the HWSP was plagued by the effort
>> of read ordering on VT-d; we would read the WRITE pointer from the HWSP
>> before it had completed writing the CSB contents. The mystery comes down
>> to the lack of rmb() for correct ordering with respect to the writes
>> from HW, and with that resolved we can remove the VT-d special casing.
>
> Mika's been able to reproduce the VT-d issue and is soak testing this
> fix, so I'll leave that until he's had a chance to confirm it survives.
> In the meantime, I think we are reasonably happy this is the right fix
> for Cannonlake and beyond, so I've pushed the first two patches.
>

My kbl was quite sensitive to this, sometimes failing to even
boot without the vtd backoff.

Now after weekend of gem_ctx_switch and gem_exec_whisper
I am confident for,

Tested-by: Mika Kuoppala <mika.kuopp...@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuopp...@linux.intel.com>
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