Re: [Intel-gfx] [PATCH 0/1] Replace shmem memory region and object backend with TTM

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 27/04/2022 12:34, Adrian Larumbe wrote:
> This patch is an attempt at eliminating the old shmem memory region and GEM
> object backend, in favour of a TTM-based one that is able to manage objects
> placed on both system and local memory.
> 
> Known issues:
> 
> Many GPU hungs in machines of GEN <= 5. My assumption is this has something
>   to do with a caching issues, but everywhere across the TTM backend code
>   I've tried to handle object creation and getting its pages with the same
>   set of caching and coherency properties as in the old shmem backend.
> 
> Object passed to shmem_create_from_object somehow not being flushed after
>   being written into at lrc_init_state. Seems thatwith the new backend and
>   when pinning an intel_context, either i915_gem_object_pin_map is not
>   creating a kernel mapping with the right caching properties or else
>   flushing it afterwards doesn't do anything.
> 
>   This leads to a GPU hung because the engine's default state that is read
>   with shmem_read doesn't reflect what had been written into it previously
>   by vmap'ing the object's pages. The only workaround I could find was
>   manually setting the shmem file's pages dirty and putting them back, but
>   this looks hacky and wasteful for big BO's

Aside, sounds like RFC would be the appropriate classification for the 
series.

But anyway, the thing I need to mention - how is THP support in the TTM 
backend? If not there it is something we absolutely need to have in 
order to avoid serious perf regressions.

It's the i915_gemfs_init call your patch removes. Even though you do 
leave the unused file dangling.

Regards,

Tvrtko

> Besides all this, I haven't yet implemented the pread callback for TTM
> object backend, as it seems CI's BAT test list doesn't include it.
> 
> Adrian Larumbe (1):
>    drm/i915: Replace shmem memory region and object backend with TTM
> 
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c   |  12 +-
>   drivers/gpu/drm/i915/gem/i915_gem_mman.c     |  32 +-
>   drivers/gpu/drm/i915/gem/i915_gem_object.h   |   2 +-
>   drivers/gpu/drm/i915/gem/i915_gem_phys.c     |   5 +-
>   drivers/gpu/drm/i915/gem/i915_gem_shmem.c    | 397 +------------------
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c      | 212 +++++++++-
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.h      |   3 +
>   drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c |  11 +-
>   drivers/gpu/drm/i915/gt/shmem_utils.c        |  64 ++-
>   drivers/gpu/drm/i915/intel_memory_region.c   |   7 +-
>   10 files changed, 333 insertions(+), 412 deletions(-)
>