drm/scheduler for vc5

[Christian König]

Am 02.04.2018 um 20:49 schrieb Eric Anholt:
> [SNIP]
>> This call will pick a VMID and remember that the process of the job is
>> now the owner of this VMID. If the VMID previously didn't belonged to
>> the process of the current job all fences of the old process are added
>> to the job->sync object again.
> This makes some sense when you have many VMIDs and reuse won't happen
> very often.  I'm concerned that when I effectively have one VMID that I
> need to keep swapping, then we're creating a specific serialization of
> the jobs at the time they're submitted to the kernel (dependency()
> callback) rather than when the scheduler decides it would like to submit
> to the HW (run_job() callback after deciding on a job based on
> priority).

We have the same problem, e.g. a currently active process on a VMID 
would get an unfair advantage because you don't need to switch between 
page tables for its submissions.

That is avoided by remembering the submission as user of a VMID as soon 
as it asks for it and not when the job is actually run. This way the 
current submission will be guaranteed to get a chance with the MMU.

Regards,
Christian.