Am 04.04.2018 um 01:08 schrieb Eric Anholt:
Christian König <christian.koenig@xxxxxxx> writes:
Hi Eric,
nice to see that the scheduler gets used more and more.
The feature your need to solve both your binning/rendering as well as
your MMU problem is dependency handling. See the "dependency" callback
of the backend operations.
With this callback the driver can return dma_fences which need to signal
(or at least be scheduled if it targets the same ring buffer/fifo).
Now you need dma_fences as result of your run_job callback for the
binning step anyway. So when you return this fence from the binning step
as dependency for your rendering step the scheduler does exactly what
you want, e.g. not start the rendering before the binning is finished.
It looks like in order to use the bin's fence returned from run_job,
render first needs to depend on exec->bin.base.s_fence->scheduled so
that run_job has been called. Is there any reason not to just depend on
exec->bin.base.s_fence->finished, instead? Finished will be signaled
basically immediately after the run_job fence completes, right?
Yes exec->bin.base.s_fence->finished should be sufficient as well.
See there are three fences involved in the scheduler:
1. The hardware fence returned by the run_job callback.
The scheduler will register on that one to be notified for completion so
that it can schedule the next job.
If you use the timeout feature it can be that we push a job to the
hardware multiple times and replace this fence when we do so.
2. s_fence->scheduled this one is signaled when the scheduler has picked
up a job.
It is the first one signaled and generally means that the job entered
the hardware fifo.
3. s_fence->finished this one is signaled when the underlying hardware
fence is signaled.
The difference to the hardware fence is that it is created much earlier
during command submission.
I should probably write all this into some kind of documentation.
Regards,
Christian.
Also, I hadn't quite followed your suggestion about MMU switching
before. Your trick was that you return a newly-generated dependency on
MMU switching as the final dependency, so that you only decide on
serializing the MMU switch once you're ready to run and the scheduler
was about to pick your job anyway. This seems good to me.
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