2022-06-21 20:03:08

by Bob Beckett

Subject: [PATCH v8 03/10] drm/i915/ttm: only trust snooping for dgfx when deciding default cache_level

By default i915_ttm_cache_level() decides I915_CACHE_LLC if HAS_SNOOP.
This is divergent from existing backends code which only considers
HAS_LLC.
Testing shows that trusting snooping on gen5- is unreliable and bsw via
ggtt mappings, so limit DGFX for now and maintain previous behaviour.

Signed-off-by: Robert Beckett <[email protected]>
---
drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
index 4c1de0b4a10f..40249fa28a7a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
@@ -46,7 +46,9 @@ static enum i915_cache_level
i915_ttm_cache_level(struct drm_i915_private *i915, struct ttm_resource *res,
struct ttm_tt *ttm)
{
- return ((HAS_LLC(i915) || HAS_SNOOP(i915)) &&
+ bool can_snoop = HAS_SNOOP(i915) && IS_DGFX(i915);
+
+ return ((HAS_LLC(i915) || can_snoop) &&
!i915_ttm_gtt_binds_lmem(res) &&
ttm->caching == ttm_cached) ? I915_CACHE_LLC :
I915_CACHE_NONE;
--
2.25.1

2022-06-22 10:55:35

by Thomas Hellström

Subject: Re: [PATCH v8 03/10] drm/i915/ttm: only trust snooping for dgfx when deciding default cache_level

On 6/21/22 22:00, Robert Beckett wrote:
> By default i915_ttm_cache_level() decides I915_CACHE_LLC if HAS_SNOOP.
> This is divergent from existing backends code which only considers
> HAS_LLC.
> Testing shows that trusting snooping on gen5- is unreliable and bsw via
> ggtt mappings, so limit DGFX for now and maintain previous behaviour.
Yeah, IIRC Matthew mentioned that HAS_SNOOP() can be overridden in
various ways, but not on DGFX, (at least not for DG1). So this looks
correct to me.
>
> Signed-off-by: Robert Beckett <[email protected]>

Reviewed-by: Thomas Hellström <[email protected]>


> ---
> drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> index 4c1de0b4a10f..40249fa28a7a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> @@ -46,7 +46,9 @@ static enum i915_cache_level
> i915_ttm_cache_level(struct drm_i915_private *i915, struct ttm_resource *res,
> struct ttm_tt *ttm)
> {
> - return ((HAS_LLC(i915) || HAS_SNOOP(i915)) &&
> + bool can_snoop = HAS_SNOOP(i915) && IS_DGFX(i915);
> +
> + return ((HAS_LLC(i915) || can_snoop) &&
> !i915_ttm_gtt_binds_lmem(res) &&
> ttm->caching == ttm_cached) ? I915_CACHE_LLC :
> I915_CACHE_NONE;