[Intel-gfx] gen7 missed IRQ workaround series.

Keith Packard keithp at keithp.com
Wed Jan 4 00:38:25 CET 2012

On Wed, 4 Jan 2012 00:04:18 +0100, Daniel Vetter <daniel at ffwll.ch> wrote:

> I kinda prefer Chris' approach of sticking with irqs, but backing it up
> with a timer in the msec range. Can't find that patch though atm (iirc
> it's in bugzilla somewhere).

I think we've resolved that the interrupt arrives, but that it is not
serialized wrt the memory write. So, what I'd love to see is whether
waiting for the irq and then busy looping for 'a while' works. This
would allow for long-running operations to idle the CPU and then hit the
interrupt and spin until the memory write is recognized.

Any solution which can leave operations unacknowledged for 'ms'
timeframes seems like a potential for serious performance
problems. Eric's simple spinning approach seems fine for the BLT ring
which we don't use that often; something more complicated and yet not
entirely timer-based might be more efficient for longer-running operations.

keith.packard at intel.com
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