Hi,
On 06/05/2021 22:13, Matthew Brost wrote:
Basic GuC submission support. This is the first bullet point in the
upstreaming plan covered in the following RFC [1].
At a very high level the GuC is a piece of firmware which sits between
the i915 and the GPU. It offloads some of the scheduling of contexts
from the i915 and programs the GPU to submit contexts. The i915
communicates with the GuC and the GuC communicates with the GPU.
May I ask what will GuC command submission do that execlist won't/can't
do? And what would be the impact on users? Even forgetting the troubled
history of GuC (instability, performance regression, poor level of user
support, 6+ years of trying to upstream it...), adding this much code
and doubling the amount of validation needed should come with a
rationale making it feel worth it... and I am not seeing here. Would you
mind providing the rationale behind this work?
GuC submission will be disabled by default on all current upstream
platforms behind a module parameter - enable_guc. A value of 3 will
enable submission and HuC loading via the GuC. GuC submission should
work on all gen11+ platforms assuming the GuC firmware is present.
What is the plan here when it comes to keeping support for execlist? I
am afraid that landing GuC support in Linux is the first step towards
killing the execlist, which would force users to use proprietary
firmwares that even most Intel engineers have little influence over.
Indeed, if "drm/i915/guc: Disable semaphores when using GuC scheduling"
which states "Disable semaphores when using GuC scheduling as semaphores
are broken in the current GuC firmware." is anything to go by, it means
that even Intel developers seem to prefer working around the GuC
firmware, rather than fixing it.