Replying with some more information for benefit of archives.
On 20/09/2019 22:29, Chris Wilson wrote:
Quoting Summers, Stuart (2019-09-20 22:09:46)
On Thu, 2019-09-19 at 08:00 +0100, Tvrtko Ursulin wrote:
On 18/09/2019 18:31, Stuart Summers wrote:
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110559
Unless there was some discussion I missed we can't just turn it on
to
work around a SKIP in IGT. Feature was deliberately limited to
Icelake
and even there just to a sub-set of possible configurations.
No conversation was missed, or at least none I was a part of. Is there
a reason we don't allow this on future platforms?
We do claim powergate support on TGL, so I assumed it would be good to
take this path on that platform. Maybe I'm misunderstanding something
here though.
The current interface is purely to work around a silicon issue on icl.
It was not developed into a fully reconfigurable sseu interface mostly
due to a lack of demonstrable need and a lack of appreciation of the
tradeoffs between different system users (along with the claim that this
is all meant to be handled by instructions in the command stream...).
For the record and from my memory, the demonstrated need pre-gen11 was
from the media transcoding side where it benefited performance for some
workload types. What wasn't clear was the best strategy of striking a
balance between increased cost of context switching (between contexts
with different sseu configs) and performance benefit of going with
reduced sseu. Again from memory, the best option looked to be a hybrid
solution of not re-configuring SSEU on every context switch, but done
periodically from an external entity, based on workload types input. As
such it did not align completely with the per-context controls.
Another team did try to autoadjust sseu but also did not produce the
rationale nor attempt to integrate with the existing code.
I forgot about this one, wonder what happened there. This was also for
pre-gen11 but with demonstrated performance-per-Watt benefit for some 3d
workloads on Android. This was known as "Dynamic SSEU".
Regards,
Tvrtko
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