[Mesa-dev] [PATCH 16/20] radeonsi: add FMASK texture binding slots and resource setup

[Christian König]

Am 09.08.2013 20:06, schrieb Marek Olšák:
> [SNIP]
> What if I kept the current emission code, and only allocated a new
> buffer at the end of the emit function, copied all descriptors to it
> using CP_DMA or COPY_DATA, and pointed SPI_SHADER_USER_DATA to it. The
> buffer where the descriptors are updated using WRITE_DATA would act as
> a staging buffer only and shaders would always read from the fresh new
> copy. Does that sound good to you?

That sounds like the solution with multiple buffers I already suggest, 
but I would rather use some RCU approach to it. Basically we just have 
to handle it like the context based resources on earlier asics. So to me 
a proper solution should look something like this:

We allocate a ring of (let's say) 16 slots for descriptor arrays, fill 
the first slot with WRITE_DATA packets and then use it in a draw command.

As soon as any of the descriptors is about to change we copy it's 
content to the next slot, let the SPI_SHADER_USER_DATA point to it, make 
the necessary updates using WRITE_DATA and then use it in a draw command.

This repeats over and over again, all we need to make sure is that we 
have enough slots in the ring to be sure that we never override 
descriptors when they are still in use, but I'm pretty sure that we 
should be on the save side with 16 or so.

We can even prepare the commands for the switch from one slot to the 
next only once and then use it for the whole lifetime of the driver.

Christian.