Re: [igt-dev] [Intel-gfx] [PATCH i-g-t] i915/gem_exec_balancer: Exercise bonded-payload synchronisation

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 05/03/2020 11:15, Chris Wilson wrote:
> Our goal with bonded submission is to submit the pair of user batches to
> the HW at roughly the same time, and trying to avoid any bubbles. If we
> submit the secondary batch too early, it will be running before the
> first and stuck on the HW preventing others from utilising the GPU. At
> worst, it may even appear unresponsive and trigger a GPU hang as it
> waits for its master. If we submit the secondary too late, the reverse
> situation may apply to the master as it has to wait to the secondaries.
> 
> This test tries to verify that using a submit-fence to create a bonded
> pair does not prevent others from using the HW. By using a pair of
> spinners, we can create a bonded hog that when set in motion will fully
> utilize both engines [if the scheduling is incorrect]. We then use a
> third party submitted after the bonded pair to cancel the spinner from
> the GPU -- if it is unable to run, the spinner is never cancelled, and
> the bonded pair will cause a GPU hang.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   tests/i915/gem_exec_balancer.c | 91 ++++++++++++++++++++++++++++++++++
>   1 file changed, 91 insertions(+)
> 
> diff --git a/tests/i915/gem_exec_balancer.c b/tests/i915/gem_exec_balancer.c
> index 69f0100ff..e1f9ce625 100644
> --- a/tests/i915/gem_exec_balancer.c
> +++ b/tests/i915/gem_exec_balancer.c
> @@ -1240,6 +1240,94 @@ static void indices(int i915)
>   	gem_quiescent_gpu(i915);
>   }
>   
> +static void __bonded_early(int i915, uint32_t ctx,
> +			   const struct i915_engine_class_instance *siblings,
> +			   unsigned int count)
> +{
> +	uint32_t handle = batch_create(i915);
> +	struct drm_i915_gem_exec_object2 batch = {
> +		.handle = handle,
> +	};
> +	struct drm_i915_gem_execbuffer2 execbuf = {
> +		.buffers_ptr = to_user_pointer(&batch),
> +		.buffer_count = 1,
> +		.rsvd1 = ctx,
> +	};
> +	igt_spin_t *spin;
> +
> +	/* A: spin forever on engine 1 */
> +	set_load_balancer(i915, ctx, siblings, count, NULL);
> +	spin = igt_spin_new(i915,
> +			    .ctx = ctx,
> +			    .engine = 1,
> +			    .flags = IGT_SPIN_NO_PREEMPTION);
> +
> +	/* B: runs after A on engine 1 */
> +	execbuf.flags = I915_EXEC_FENCE_OUT;
> +	execbuf.flags |= 1;
> +	gem_execbuf_wr(i915, &execbuf);
> +
> +	/* B': run in parallel with B on engine 2, i.e. not before A! */
> +	set_load_balancer(i915, ctx, siblings, count, NULL);
> +	execbuf.flags = I915_EXEC_FENCE_SUBMIT | I915_EXEC_FENCE_OUT;
> +	execbuf.flags |= 2;
> +	execbuf.rsvd2 >>= 32;
> +	gem_execbuf_wr(i915, &execbuf);
> +
> +	/* C: prevent anything running on engine 2 after B' */
> +	spin->execbuf.flags = 2;
> +	gem_execbuf(i915, &spin->execbuf);
> +
> +	igt_debugfs_dump(i915, "i915_engine_info");
> +
> +	/* D: cancel the spinner from engine 2 (new timeline) */
> +	set_load_balancer(i915, ctx, siblings, count, NULL);
> +	batch.handle = create_semaphore_to_spinner(i915, spin);
> +	execbuf.flags = 2;
> +	gem_execbuf(i915, &execbuf);
> +	gem_close(i915, batch.handle);
> +
> +	/* If C runs before D, we never cancel the spinner and so hang */
> +	gem_sync(i915, handle);
> +
> +	/* Check the bonded pair completed successfully */
> +	igt_assert_eq(sync_fence_status(execbuf.rsvd2 & 0xffffffff), 1);
> +	igt_assert_eq(sync_fence_status(execbuf.rsvd2 >> 32), 1);
> +
> +	close(execbuf.rsvd2);
> +	close(execbuf.rsvd2 >> 32);
> +
> +	gem_close(i915, handle);
> +	igt_spin_free(i915, spin);
> +}
> +
> +static void bonded_early(int i915)
> +{
> +	uint32_t ctx;
> +
> +	/*
> +	 * Our goal is to start the bonded payloads at roughly the same time.
> +	 * We do not want to start the secondary batch too early as it will
> +	 * do nothing but hog the GPU until the first has a chance to execute.
> +	 * So if we were to arbitrary delay the first by running it after a
> +	 * spinner...
> +	 */
> +
> +	ctx = gem_context_create(i915);
> +
> +	for (int class = 0; class < 32; class++) {
> +		struct i915_engine_class_instance *siblings;
> +		unsigned int count;
> +
> +		siblings = list_engines(i915, 1u << class, &count);
> +		if (count > 1)
> +			__bonded_early(i915, ctx, siblings, count);
> +		free(siblings);
> +	}
> +
> +	gem_context_destroy(i915, ctx);
> +}
> +
>   static void busy(int i915)
>   {
>   	uint32_t scratch = gem_create(i915, 4096);
> @@ -1891,6 +1979,9 @@ igt_main
>   	igt_subtest("bonded-semaphore")
>   		bonded_semaphore(i915);
>   
> +	igt_subtest("bonded-early")
> +		bonded_early(i915);
> +
>   	igt_fixture {
>   		igt_stop_hang_detector();
>   	}
> 

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

Regards,

Tvrtko
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