[Mesa-dev] [PATCH 4/5] r600g, radeonsi: Use write-combined persistent GTT mappings

[Grigori Goronzy]

On 18.07.2014 13:45, Marek Olšák wrote:
> If the requirements of GL_MAP_COHERENT_BIT are satisfied, then the
> patch is okay.
>

Apart from correctness, I still wonder how this will affect performance,
most notably CPU reads. This change unconditionally uses write-combined,
uncached memory for MAP_COHERENT buffers. Unless I am missing something,
CPU reads will be slow, even if the buffer storage flags indicate that
the buffer will be read by the CPU. Maybe it's a good idea to avoid
write combined memory if the buffer storage flags include MAP_READ_BIT?

Grigori

> Marek
> 
> 
> On Fri, Jul 18, 2014 at 5:19 AM, Michel Dänzer <michel at daenzer.net> wrote:
>> On 17.07.2014 21:00, Marek Olšák wrote:
>>> On Thu, Jul 17, 2014 at 12:01 PM, Michel Dänzer <michel at daenzer.net> wrote:
>>>> From: Michel Dänzer <michel.daenzer at amd.com>
>>>>
>>>> This is hopefully safe: The kernel makes sure writes to these mappings
>>>> finish before the GPU might start reading from them, and the GPU caches
>>>> are invalidated at the start of a command stream.
>>>>
>>> The resource flags actually tell you what you can do. If the COHERENT
>>> flag is set, the mapping must be cached.
>>
>> Why is that required? As I explain above, we should satisfy the
>> requirements of the ARB_buffer_storage extension AFAICT.
>>
>>
>> As pointed out by you and Grigori in other posts, I should probably just
>> drop the special treatment of persistent mappings though, so the
>> placement and flags are derived from the buffer usage.
>>
>>
>> --
>> Earthling Michel Dänzer            |                  http://www.amd.com
>> Libre software enthusiast          |                Mesa and X developer
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
> 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 246 bytes
Desc: OpenPGP digital signature
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20140718/25c84a2b/attachment.sig>