[Intel-gfx] [PATCH 11/66] drm/i915: Preallocate stashes for vma page-directories

[Thomas Hellström (Intel)]

On 2020-07-15 13:50, Chris Wilson wrote:
> We need to make the DMA allocations used for page directories to be
> performed up front so that we can include those allocations in our
> memory reservation pass. The downside is that we have to assume the
> worst case, even before we know the final layout, and always allocate
> enough page directories for this object, even when there will be overlap.
> This unfortunately can be quite expensive, especially as we have to
> clear/reset the page directories and DMA pages, but it should only be
> required during early phases of a workload when new objects are being
> discovered, or after memory/eviction pressure when we need to rebind.
> Once we reach steady state, the objects should not be moved and we no
> longer need to preallocating the pages tables.
>
> It should be noted that the lifetime for the page directories DMA is
> more or less decoupled from individual fences as they will be shared
> across objects across timelines.
>
> v2: Only allocate enough PD space for the PTE we may use, we do not need
> to allocate PD that will be left as scratch.
> v3: Store the shift unto the first PD level to encapsulate the different
> PTE counts for gen6/gen8.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Matthew Auld <matthew.auld at intel.com>
> ---
>   .../gpu/drm/i915/gem/i915_gem_client_blt.c    | 11 +--
>   drivers/gpu/drm/i915/gt/gen6_ppgtt.c          | 40 ++++-----
>   drivers/gpu/drm/i915/gt/gen8_ppgtt.c          | 78 +++++------------
>   drivers/gpu/drm/i915/gt/intel_ggtt.c          | 60 ++++++--------
>   drivers/gpu/drm/i915/gt/intel_gtt.h           | 46 ++++++----
>   drivers/gpu/drm/i915/gt/intel_ppgtt.c         | 83 ++++++++++++++++---
>   drivers/gpu/drm/i915/i915_vma.c               | 27 +++---
>   drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 60 ++++++++------
>   drivers/gpu/drm/i915/selftests/mock_gtt.c     | 22 ++---
>   9 files changed, 237 insertions(+), 190 deletions(-)

Hi, Chris,

Overall looks good, but a question: Why can't we perform page-table 
memory allocation on demand when needed?

Are we then under a mutex that we also take during reclaim?

/Thomas