[Intel-gfx] [PATCH 2/4] drm/i915: Let hangcheck score decay faster than loop increment

[Mika Kuoppala]

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

> On Mon, Nov 30, 2015 at 06:53:07PM +0200, Mika Kuoppala wrote:
>> We decay hangcheck score, instead of setting it to zero,
>> when seqno moves forward. This was added as mechanism to
>> detect batches full of invalid waits.
>
> And slow DoS. So no.

Point was to decay faster than 'loop detection' (-2) but slower
than kicking (+5) to keep the score decaying even if there is
one 'loop detection' per batch.

The criticism about pipe control (patch 1/4) is warranted as it just
happens to help now when the synchronization happens on ring, and thus
only helps with batches that follow this pattern wrt pipe control.

I will post a patch that tries to achieve more generic way
by inspecting subunit states if head seems to be stuck, so
that substitutes 1/4. And also makes 4/4 even more moot.

There is not much to salvage in this series so please ignore.

Thanks,
-Mika

> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre