[Intel-gfx] [PATCH] drm/i915/selftests: keep same cache settings as timeline

[Matt Roper]

On Wed, Mar 15, 2023 at 11:08:00AM -0700, fei.yang at intel.com wrote:
> From: Fei Yang <fei.yang at intel.com>
> 
> On MTL, objects allocated through i915_gem_object_create_internal() are
> mapped as uncached in GPU by default because HAS_LLC is false. However
> in the live_hwsp_read selftest these watcher objects are mapped as WB
> on CPU side. The conseqence is that the updates done by the GPU are not
> immediately visible to CPU, thus the selftest is randomly failing due to
> the stale data in CPU cache. Solution can be either setting WC for CPU +
> UC for GPU, or WB for CPU + 1-way coherent WB for GPU.
> To keep the consistency, let's simply inherit the same cache settings
> from the timeline, which is WB for CPU + 1-way coherent WB for GPU,
> because this test is supposed to emulate the behavior of the timeline
> anyway.
> 
> Signed-off-by: Fei Yang <fei.yang at intel.com>

It looks like there might be an indentation mistake on the second line
of the i915_gem_object_pin_map_unlocked() call, but we can fix that up
while applying; no need to re-send.

Reviewed-by: Matt Roper <matthew.d.roper at intel.com>

Is there an FDO issue # for the random failures thar were being seen?
If so, we should add a Closes: or References: tag here.


Matt

> ---
>  drivers/gpu/drm/i915/gt/selftest_timeline.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/selftest_timeline.c b/drivers/gpu/drm/i915/gt/selftest_timeline.c
> index 522d0190509c..631aaed9bc3d 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_timeline.c
> @@ -825,7 +825,8 @@ static bool cmp_gte(u32 a, u32 b)
>  	return a >= b;
>  }
>  
> -static int setup_watcher(struct hwsp_watcher *w, struct intel_gt *gt)
> +static int setup_watcher(struct hwsp_watcher *w, struct intel_gt *gt,
> +			 struct intel_timeline *tl)
>  {
>  	struct drm_i915_gem_object *obj;
>  	struct i915_vma *vma;
> @@ -834,7 +835,10 @@ static int setup_watcher(struct hwsp_watcher *w, struct intel_gt *gt)
>  	if (IS_ERR(obj))
>  		return PTR_ERR(obj);
>  
> -	w->map = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB);
> +	/* keep the same cache settings as timeline */
> +	i915_gem_object_set_cache_coherency(obj, tl->hwsp_ggtt->obj->cache_level);
> +	w->map = i915_gem_object_pin_map_unlocked(obj,
> +			page_unmask_bits(tl->hwsp_ggtt->obj->mm.mapping));
>  	if (IS_ERR(w->map)) {
>  		i915_gem_object_put(obj);
>  		return PTR_ERR(w->map);
> @@ -1004,8 +1008,10 @@ static int live_hwsp_read(void *arg)
>  	if (!tl->has_initial_breadcrumb)
>  		goto out_free;
>  
> +	selftest_tl_pin(tl);
> +
>  	for (i = 0; i < ARRAY_SIZE(watcher); i++) {
> -		err = setup_watcher(&watcher[i], gt);
> +		err = setup_watcher(&watcher[i], gt, tl);
>  		if (err)
>  			goto out;
>  	}
> @@ -1160,6 +1166,8 @@ static int live_hwsp_read(void *arg)
>  	for (i = 0; i < ARRAY_SIZE(watcher); i++)
>  		cleanup_watcher(&watcher[i]);
>  
> +	intel_timeline_unpin(tl);
> +
>  	if (igt_flush_test(gt->i915))
>  		err = -EIO;
>  
> -- 
> 2.25.1
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation