Re: [igt-dev] [Intel-gfx] [PATCH i-g-t] i915/gem_ctx_shared: Check for a large enough hole in the GTT

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Cc: igt-dev@lists.freedesktop.org
Subject: Re: [igt-dev] [Intel-gfx] [PATCH i-g-t] i915/gem_ctx_shared: Check for a large enough hole in the GTT
Date: Mon, 17 Jun 2019 15:25:05 +0100	[thread overview]
Message-ID: <b2b26762-5c52-442a-2278-7588bb6190b4@linux.intel.com> (raw)
In-Reply-To: <20190617111457.9226-1-chris@chris-wilson.co.uk>


On 17/06/2019 12:14, Chris Wilson wrote:
> In the exec-shared-gtt test, we cheekily try to reference an object we
> placed in the GTT in an earlier execbuf (and avoid declaring it in the
> later call). For a global GTT, where there may be existing objects, we
> have to find a hole large enough to fit both and avoid and implicit
> guard pages.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110876
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   tests/i915/gem_ctx_shared.c | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/tests/i915/gem_ctx_shared.c b/tests/i915/gem_ctx_shared.c
> index ed43e8903..4b1020b96 100644
> --- a/tests/i915/gem_ctx_shared.c
> +++ b/tests/i915/gem_ctx_shared.c
> @@ -184,6 +184,7 @@ static void exhaust_shared_gtt(int i915, unsigned int flags)
>   static void exec_shared_gtt(int i915, unsigned int ring)
>   {
>   	const int gen = intel_gen(intel_get_drm_devid(i915));
> +	const uint32_t bbe = MI_BATCH_BUFFER_END;
>   	struct drm_i915_gem_exec_object2 obj = {};
>   	struct drm_i915_gem_execbuffer2 execbuf = {
>   		.buffers_ptr = to_user_pointer(&obj),
> @@ -197,11 +198,19 @@ static void exec_shared_gtt(int i915, unsigned int ring)
>   	gem_require_ring(i915, ring);
>   	igt_require(gem_can_store_dword(i915, ring));
>   
> +	/* Find a hole big enough for both objects later */
> +	scratch = gem_create(i915, 16384);
> +	gem_write(i915, scratch, 0, &bbe, sizeof(bbe));
> +	obj.handle = scratch;
> +	gem_execbuf(i915, &execbuf);
> +	gem_close(i915, scratch);
> +	obj.flags |= EXEC_OBJECT_PINNED; /* reuse this address */
> +
>   	scratch = gem_create(i915, 4096);
>   	s = gem_mmap__cpu(i915, scratch, 0, 4096, PROT_WRITE);
>   
>   	gem_set_domain(i915, scratch, I915_GEM_DOMAIN_CPU, I915_GEM_DOMAIN_CPU);
> -	*s = MI_BATCH_BUFFER_END;
> +	*s = bbe;
>   
>   	/* Load object into place in the GTT */
>   	obj.handle = scratch;
> @@ -224,11 +233,10 @@ static void exec_shared_gtt(int i915, unsigned int ring)
>   		batch[++i] = obj.offset;
>   	}
>   	batch[++i] = 0xc0ffee;
> -	batch[++i] = MI_BATCH_BUFFER_END;
> +	batch[++i] = bbe;
>   	gem_write(i915, obj.handle, 0, batch, sizeof(batch));
>   
> -	obj.offset += 4096; /* make sure we don't cause an eviction! */
> -	obj.flags |= EXEC_OBJECT_PINNED;
> +	obj.offset += 8192; /* make sure we don't cause an eviction! */
>   	execbuf.rsvd1 = gem_context_clone(i915, 0, I915_CONTEXT_CLONE_VM, 0);
>   	if (gen > 3 && gen < 6)
>   		execbuf.flags |= I915_EXEC_SECURE;
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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