[PATCH] drm/ttm: do not try to preserve caching state

[Jerome Glisse]

On Wed, Nov 28, 2012 at 10:05 AM,  <j.glisse at gmail.com> wrote:
> From: Jerome Glisse <jglisse at redhat.com>
>
> It make no sense to preserve caching state especialy when
> moving from vram to system. It burden the page allocator to
> match the vram caching (often WC) which just burn CPU cycle
> for no good reasons.
>
> Signed-off-by: Jerome Glisse <jglisse at redhat.com>
> ---
>  drivers/gpu/drm/ttm/ttm_bo.c | 15 +++------------
>  1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index bf6e4b5..39dcc58 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -896,19 +896,12 @@ static int ttm_bo_mem_force_space(struct ttm_buffer_object *bo,
>  }
>
>  static uint32_t ttm_bo_select_caching(struct ttm_mem_type_manager *man,
> -                                     uint32_t cur_placement,
>                                       uint32_t proposed_placement)
>  {
>         uint32_t caching = proposed_placement & TTM_PL_MASK_CACHING;
>         uint32_t result = proposed_placement & ~TTM_PL_MASK_CACHING;
>
> -       /**
> -        * Keep current caching if possible.
> -        */
> -
> -       if ((cur_placement & caching) != 0)
> -               result |= (cur_placement & caching);
> -       else if ((man->default_caching & caching) != 0)
> +       if ((man->default_caching & caching) != 0)
>                 result |= man->default_caching;
>         else if ((TTM_PL_FLAG_CACHED & caching) != 0)
>                 result |= TTM_PL_FLAG_CACHED;
> @@ -978,8 +971,7 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
>                 if (!type_ok)
>                         continue;
>
> -               cur_flags = ttm_bo_select_caching(man, bo->mem.placement,
> -                                                 cur_flags);
> +               cur_flags = ttm_bo_select_caching(man, cur_flags);
>                 /*
>                  * Use the access and other non-mapping-related flag bits from
>                  * the memory placement flags to the current flags
> @@ -1023,8 +1015,7 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
>                                                 &cur_flags))
>                         continue;
>
> -               cur_flags = ttm_bo_select_caching(man, bo->mem.placement,
> -                                                 cur_flags);
> +               cur_flags = ttm_bo_select_caching(man, cur_flags);
>                 /*
>                  * Use the access and other non-mapping-related flag bits from
>                  * the memory placement flags to the current flags
> --
> 1.7.11.7
>

Note this is mostly to mitigate performance decrease when a lot of
eviction happen. It increase perf by as much of 60% on my computer.

Cheers,
Jerome