[Intel-xe] [PATCH v6 0/5] PAT and cache coherency support

[Matthew Auld]

On 28/09/2023 21:02, Souza, Jose wrote:
> On Thu, 2023-09-28 at 12:40 -0700, José Roberto de Souza wrote:
>> On Thu, 2023-09-28 at 11:05 +0100, Matthew Auld wrote:
>>> Branch available here:
>>> https://gitlab.freedesktop.org/mwa/kernel/-/tree/xe-pat-index?ref_type=heads
>>>
>>> Goal here is to allow userspace to directly control the pat_index when mapping
>>> memory via the ppGTT, in addtion to the CPU caching mode. This is very much
>>> needed on newer igpu platforms which allow incoherent GT access, where the
>>> choice over the cache level and expected coherency is best left to userspace
>>> depending on their usecase.  In the future there may also be other stuff encoded
>>> in the pat_index, so giving userspace direct control will also be needed there.
>>>
>>> To support this we added new gem_create uAPI for selecting the CPU cache
>>> mode to use for system memory, including the expected GPU coherency mode. There
>>> are various restrictions here for the selected coherency mode and compatible CPU
>>> cache modes.  With that in place the actual pat_index can now be provided as
>>> part of vm_bind. The only restriction is that the coherency mode of the
>>> pat_index must be at least as coherent as the gem_create coherency mode. There
>>> are also some special cases like with userptr and dma-buf.
>>>
>>> v2:
>>>    - Loads of improvements/tweaks. Main changes are to now allow
>>>      gem_create.coh_mode <= coh_mode(pat_index), rather than it needing to match
>>>      exactly. This simplifies the dma-buf policy from userspace pov. Also we now
>>>      only consider COH_NONE and COH_AT_LEAST_1WAY.
>>> v3:
>>>    - Rebase. Split the pte_encode() refactoring, plus various smaller tweaks and
>>>      fixes.
>>> v4:
>>>    - Rebase on Lucas' new series.
>>>    - Drop UC cache mode.
>>>    - s/smem_cpu_caching/cpu_caching/. Idea is to make VRAM WC explicit in the
>>>      uapi, plus make it more future proof.
>>> v5:
>>>    - Rebase, plus some small tweaks and fixes.
>>> v6:
>>>    - CI hooks fixes + checkpatch.
>>>
>>
>> With comment in patch 3/6 fixed this series is:
>> Reviewed-by: José Roberto de Souza <jose.souza at intel.com>
>> Tested-by: José Roberto de Souza <jose.souza at intel.com>
> 
> Here the Mesa implementation: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25462

Thanks.

> 
>>
>> Thank you
>