[igt-dev] [RFC PATCH i-g-t v4 4/4] tests/gem_ctx_shared: Align objects using minimum GTT alignment

[Chris Wilson]

Quoting Janusz Krzysztofik (2019-10-31 15:28:57)
> exec-shared-gtt-* subtests use hardcoded values for object size and
> softpin offset, based on 4kB GTT alignment assumption.  That may result
> in those subtests failing when run on future backing stores with
> possibly larger minimum page sizes.
> 
> Replace hardcoded constants with values calculated from minimum GTT
> alignment of actual backing store the test is running on.
> 
> v2: Update helper name, use 'minimum GTT alignment' term across the
>     change, adjust variable name.
> 
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  tests/i915/gem_ctx_shared.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/tests/i915/gem_ctx_shared.c b/tests/i915/gem_ctx_shared.c
> index 6d8cbcce..1e9c7f78 100644
> --- a/tests/i915/gem_ctx_shared.c
> +++ b/tests/i915/gem_ctx_shared.c
> @@ -195,6 +195,7 @@ static void exec_shared_gtt(int i915, unsigned int ring)
>         uint32_t scratch, *s;
>         uint32_t batch, cs[16];
>         uint64_t offset;
> +       uint64_t alignment;
>         int i;
>  
>         gem_require_ring(i915, ring);
> @@ -203,7 +204,8 @@ static void exec_shared_gtt(int i915, unsigned int ring)
>         clone = gem_context_clone(i915, 0, I915_CONTEXT_CLONE_VM, 0);
>  
>         /* Find a hole big enough for both objects later */
> -       scratch = gem_create(i915, 16384);
> +       alignment = 2 * gem_gtt_min_alignment(i915);
> +       scratch = gem_create(i915, 2 * alignment);
>         gem_write(i915, scratch, 0, &bbe, sizeof(bbe));
>         obj.handle = scratch;
>         gem_execbuf(i915, &execbuf);
> @@ -246,7 +248,7 @@ static void exec_shared_gtt(int i915, unsigned int ring)
>         gem_write(i915, batch, 0, cs, sizeof(cs));
>  
>         obj.handle = batch;
> -       obj.offset += 8192; /* make sure we don't cause an eviction! */
> +       obj.offset += alignment; /* make sure we don't cause an eviction! */

It's 'stride' here. It's leaving a guard page in between, just in case
page coloring demands it.
-Chris