[Mesa-dev] [PATCH 1/2] i965: add missing rollback of URB requirements

[andrey simiklit]

On Tue, Jan 8, 2019 at 1:11 PM Chris Wilson <chris at chris-wilson.co.uk>
wrote:

> Quoting Lionel Landwerlin (2019-01-08 11:03:26)
> > Hi Andrii,
> >
> > Although I think what these patches do makes sense, I think it's missing
> > the bigger picture.
> > There is a lot more state that gets lost if we have to revert all of the
> > emitted commands.
> > A quick look at brw_upload_pipeline_state() shows all of the programs
> > could be invalid as well, or the number of samples, etc...
> >
> > To me it seems like we need a much larger state save/restore.
> >
> > Ken: what do you think?
>
> How about not rolling back? If we accept it as currently broken, and just
> demand the kernel provide logical contexts for all i965 devices (just ack
> some patches!), and then just flush the batch (possibly with a dummy 3D
> prim if you want to be sure the 3D state is loaded) and rely on the
> context preserving state across batches.
> -Chris
>

Could you please provide a link to the patches you talking about?

At the moment as far as I understood the rollback system
helps to reduce quantity of the flush operations in some lucky cases.
When there isn't enough space for a batch aperture,
we will rollback the batch to the saved state,
when limit (means aperture_threshold) wasn't reached by it.

pseudo code (simple variant, without error handling):
   save batch state here;
   do
   {
       add primitives to the batch;
       if the batch size limit is exceeded
       {
           rollback to the saved batch state;
           flush the batch;
       }
       else
       {
           break;
       }
   } while(true);

Are you suggesting to flush the batch every time without waiting for a
nearly full filling of it?
Like this:
   add primitives to batch;
   flush batch;

Please correct me if I am wrong.

-Andrii


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