[Mesa-dev] [Mesa-stable] [PATCH] radeonsi: Save and restore entire CE RAM.

[Emil Velikov]

On 6 June 2016 at 16:46, Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl> wrote:
> On Mon, Jun 6, 2016 at 5:14 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> On 06.06.2016 00:28, Bas Nieuwenhuizen wrote:
>>>
>>> This fixes a problem with the CE preamble and restoring only stuff in the
>>> preamble when needed.
>>>
>>> To illustrate suppose we have two graphics IB's 1 and 2, which  are
>>> submitted in
>>> that order. Furthermore suppose IB 1 does not use CE ram, but IB 2 does,
>>> and we
>>> have a context switch at the start of IB 1, but not between IB 1 and IB 2.
>>>
>>> The old code put the CE RAM loads in the preamble of IB 2. As the preamble
>>> of
>>> IB 1 does not have the loads and the preamble of IB 2 does not get
>>> executed, the
>>> old values are not load into CE RAM.
>>>
>>> Fix this by always restoring the entire CE RAM.
>>
>>
>> Nice catch!
>>
>> Have you considered restoring from the desc->buffers instead? The
>> double-dump seems a bit redundant. But maybe it's easier this way...
>>
>> Also, do we really need to dump the entire CE RAM? After initializing the
>> descriptor sets, we should know exactly how much we need...
>
> We can do both.
>
> However, wrt using the desc->buffers, note that this results in 21
> loads (and adding potentially multiple buffers to the CS bo list)
> while the current approach is 1 load
> and 1 store. Furthermore  the CE is <= 15% busy in pretty much all
> games I tried, as measured by polling CP_STAT.CE_BUSY. As such I
> haven't really considered optimizing this GPU side and I'm not really
> sure if it is worth it in this case to do a bit more work on the CPU
> to avoid some work on the GPU.
>
> Though I'm probably overthinking this given how small an impact the
> whole CE stuff had on performance and we're now talking about a per IB
> cost instead of per draw.
>
Gents, double-checking:
The patch has been superseded (with
54f755fa0fda14c578022767bcef2f27b2e89707?), correct ?

Thanks
Emil