[igt-dev] [PATCH i-g-t 02/18] lib/intel_batchbuffer: Add control over fencing in intel_bb

[Chris Wilson]

Quoting Dominik Grzegorzek (2020-09-29 12:28:54)
> From: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> 
> From default intel_bb uses fencing to track subsequent execs.
> It is required to properly sync intel_bb. Unfortunately this
> also has some drawback, when we want to use same intel_bb to
> schedule some time consuming job then run something else. Fencing
> as turned on from default will serialize such execs. To avoid that
> add possibility to turn on / off fencing in the intel_bb.

I'm still getting confused by this. I don't see where you are
serialising on the old fence, you are just merging the fences for later
waits. That does mean that wait does wait for all, both the short and
long jobs, but the use of the fence is not serialising the execution of
those jobs. (Providing that the intel_bb is used in such a way to allow
for parallel execution i.e. multiple timelines from using different
contexts or independent engines.)
-Chris