Re: [PATCH 4/5] drm/i915/selftests: Exercise long preemption chains

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

On 14/11/2019 22:57, Chris Wilson wrote:
> Verify that we can execute a long chain of dependent requests from
> userspace, each one slightly more important than the last.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/selftest_lrc.c | 196 +++++++++++++++++++++++++
>   1 file changed, 196 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> index d1ed3c0f851c..2ef03a8efa28 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> @@ -1915,6 +1915,201 @@ static int live_chain_preempt(void *arg)
>   	goto err_client_lo;
>   }
>   
> +static int create_gang(struct intel_engine_cs *engine,
> +		       struct i915_request **prev)
> +{
> +	struct drm_i915_gem_object *obj;
> +	struct intel_context *ce;
> +	struct i915_request *rq;
> +	struct i915_vma *vma;
> +	u32 *cs;
> +	int err;
> +
> +	ce = intel_context_create(engine->kernel_context->gem_context, engine);
> +	if (IS_ERR(ce))
> +		return PTR_ERR(ce);
> +
> +	obj = i915_gem_object_create_internal(engine->i915, 4096);
> +	if (IS_ERR(obj)) {
> +		err = PTR_ERR(obj);
> +		goto err_ce;
> +	}
> +
> +	vma = i915_vma_instance(obj, ce->vm, NULL);
> +	if (IS_ERR(vma)) {
> +		err = PTR_ERR(vma);
> +		goto err_obj;
> +	}
> +
> +	err = i915_vma_pin(vma, 0, 0, PIN_USER);
> +	if (err)
> +		goto err_obj;
> +
> +	cs = i915_gem_object_pin_map(obj, I915_MAP_WC);
> +	if (IS_ERR(cs))
> +		goto err_obj;
> +
> +	/* Semaphore target: spin until zero */
> +	*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
> +
> +	*cs++ = MI_SEMAPHORE_WAIT |
> +		MI_SEMAPHORE_POLL |
> +		MI_SEMAPHORE_SAD_EQ_SDD;
> +	*cs++ = 0;
> +	*cs++ = lower_32_bits(vma->node.start);
> +	*cs++ = upper_32_bits(vma->node.start);
> +
> +	if (*prev) {
> +		u64 offset = (*prev)->batch->node.start;
> +
> +		/* Terminate the spinner in the next lower priority batch. */
> +		*cs++ = MI_STORE_DWORD_IMM_GEN4;
> +		*cs++ = lower_32_bits(offset);
> +		*cs++ = upper_32_bits(offset);
> +		*cs++ = 0;
> +	}
> +
> +	*cs++ = MI_BATCH_BUFFER_END;
> +	i915_gem_object_flush_map(obj);
> +	i915_gem_object_unpin_map(obj);
> +
> +	rq = intel_context_create_request(ce);
> +	if (IS_ERR(rq))
> +		goto err_obj;
> +
> +	rq->batch = vma;
> +	i915_request_get(rq);
> +
> +	i915_vma_lock(vma);
> +	err = i915_request_await_object(rq, vma->obj, false);
> +	if (!err)
> +		err = i915_vma_move_to_active(vma, rq, 0);
> +	if (!err)
> +		err = rq->engine->emit_bb_start(rq,
> +						vma->node.start,
> +						PAGE_SIZE, 0);
> +	i915_vma_unlock(vma);
> +	i915_request_add(rq);
> +	if (err)
> +		goto err_rq;
> +
> +	i915_gem_object_put(obj);
> +	intel_context_put(ce);
> +
> +	rq->client_link.next = &(*prev)->client_link;
> +	*prev = rq;
> +	return 0;
> +
> +err_rq:
> +	i915_request_put(rq);
> +err_obj:
> +	i915_gem_object_put(obj);
> +err_ce:
> +	intel_context_put(ce);
> +	return err;
> +}
> +
> +static int live_preempt_gang(void *arg)
> +{
> +	struct intel_gt *gt = arg;
> +	struct intel_engine_cs *engine;
> +	enum intel_engine_id id;
> +
> +	if (!HAS_LOGICAL_RING_PREEMPTION(gt->i915))
> +		return 0;
> +
> +	/*
> +	 * Build as long a chain of preempters as we can, with each
> +	 * request higher priority than the last. Once we are ready, we release
> +	 * the last batch which then precolates down the chain, each releasing
> +	 * the next oldest in turn. The intent is to simply push as hard as we
> +	 * can with the number of preemptions, trying to exceed narrow HW
> +	 * limits. At a minimum, we insist that we can sort all the user
> +	 * high priority levels into execution order.
> +	 */
> +
> +	for_each_engine(engine, gt, id) {
> +		struct i915_request *rq = NULL;
> +		struct igt_live_test t;
> +		IGT_TIMEOUT(end_time);
> +		int prio = 0;
> +		int err = 0;
> +		u32 *cs;
> +
> +		if (!intel_engine_has_preemption(engine))
> +			continue;
> +
> +		if (igt_live_test_begin(&t, gt->i915, __func__, engine->name))
> +			return -EIO;
> +
> +		do {
> +			struct i915_sched_attr attr = {
> +				.priority = I915_USER_PRIORITY(prio++),
> +			};
> +
> +			err = create_gang(engine, &rq);
> +			if (err)
> +				break;
> +
> +			/* Submit each spinner at increasing priority */
> +			engine->schedule(rq, &attr);
> +
> +			if (prio <= I915_PRIORITY_MAX)
> +				continue;
> +
> +			if (prio > (INT_MAX >> I915_USER_PRIORITY_SHIFT))
> +				break;
> +
> +			if (__igt_timeout(end_time, NULL))
> +				break;
> +		} while (1);
> +		pr_debug("%s: Preempt chain of %d requests\n",
> +			 engine->name, prio);
> +
> +		/*
> +		 * Such that the last spinner is the higher priority and
> +		 * should execute first. When that spinner completes,
> +		 * it will terminate the next lowest spinner until there
> +		 * are no more spinners and the gang is complete.
> +		 */
> +		cs = i915_gem_object_pin_map(rq->batch->obj, I915_MAP_WC);
> +		if (!IS_ERR(cs)) {
> +			*cs = 0;
> +			i915_gem_object_unpin_map(rq->batch->obj);
> +		} else {
> +			err = PTR_ERR(cs);
> +			intel_gt_set_wedged(gt);
> +		}
> +
> +		while (rq) { /* wait for each rq from highest to lowest prio */
> +			struct i915_request *n =
> +				list_next_entry(rq, client_link);
> +
> +			if (err == 0 && i915_request_wait(rq, 0, HZ / 5) < 0) {
> +				struct drm_printer p =
> +					drm_info_printer(engine->i915->drm.dev);
> +
> +				pr_err("Failed to flush chain of %d requests, at %d\n",
> +				       prio, rq_prio(rq) >> I915_USER_PRIORITY_SHIFT);
> +				intel_engine_dump(engine, &p,
> +						  "%s\n", engine->name);
> +
> +				err = -ETIME;
> +			}
> +
> +			i915_request_put(rq);
> +			rq = n;
> +		}
> +
> +		if (igt_live_test_end(&t))
> +			err = -EIO;
> +		if (err)
> +			return err;
> +	}
> +
> +	return 0;
> +}
> +
>   static int live_preempt_hang(void *arg)
>   {
>   	struct intel_gt *gt = arg;
> @@ -3028,6 +3223,7 @@ int intel_execlists_live_selftests(struct drm_i915_private *i915)
>   		SUBTEST(live_suppress_self_preempt),
>   		SUBTEST(live_suppress_wait_preempt),
>   		SUBTEST(live_chain_preempt),
> +		SUBTEST(live_preempt_gang),
>   		SUBTEST(live_preempt_hang),
>   		SUBTEST(live_preempt_timeout),
>   		SUBTEST(live_preempt_smoke),
> 

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

Regards,

Tvrtko
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