Re: [Intel-gfx] [PATCH 17/27] drm/i915/guc: Implement multi-lrc reset

[John Harrison <john.c.harrison@intel.com>]

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On 8/20/2021 15:44, Matthew Brost wrote:
> Update context and full GPU reset to work with multi-lrc. The idea is
> parent context tracks all the active requests inflight for itself and
> its' children. The parent context owns the reset replaying / canceling
its' -> its

> requests as needed.
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_context.c       | 11 ++--
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 63 +++++++++++++------
>   2 files changed, 51 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index 00d1aee6d199..5615be32879c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -528,20 +528,21 @@ struct i915_request *intel_context_create_request(struct intel_context *ce)
>   
>   struct i915_request *intel_context_find_active_request(struct intel_context *ce)
>   {
> +	struct intel_context *parent = intel_context_to_parent(ce);
>   	struct i915_request *rq, *active = NULL;
>   	unsigned long flags;
>   
>   	GEM_BUG_ON(!intel_engine_uses_guc(ce->engine));
Should this not check the parent as well/instead?

And to be clear, this can be called on regular contexts (where ce == 
parent) and on both the parent or child contexts of multi-LRC contexts 
(where ce may or may not match parent)?


>   
> -	spin_lock_irqsave(&ce->guc_state.lock, flags);
> -	list_for_each_entry_reverse(rq, &ce->guc_state.requests,
> +	spin_lock_irqsave(&parent->guc_state.lock, flags);
> +	list_for_each_entry_reverse(rq, &parent->guc_state.requests,
>   				    sched.link) {
> -		if (i915_request_completed(rq))
> +		if (i915_request_completed(rq) && rq->context == ce)
'rq->context == ce' means:

 1. single-LRC context, rq is owned by ce
 2. multi-LRC context, ce is child, rq really belongs to ce but is being
    tracked by parent
 3. multi-LRC context, ce is parent, rq really is owned by ce

So when 'rq->ce != ce', it means that the request is owned by a 
different child to 'ce' but within the same multi-LRC group. So we want 
to ignore that request and keep searching until we find one that is 
really owned by the target ce?

>   			break;
>   
> -		active = rq;
> +		active = (rq->context == ce) ? rq : active;
Would be clearer to say 'if(rq->ce != ce) continue;' and leave 'active = 
rq;' alone?

And again, the intention is to ignore requests that are owned by other 
members of the same multi-LRC group?

Would be good to add some documentation to this function to explain the 
above (assuming my description is correct?).

>   	}
> -	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> +	spin_unlock_irqrestore(&parent->guc_state.lock, flags);
>   
>   	return active;
>   }
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index f0b60fecf253..e34e0ea9136a 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -670,6 +670,11 @@ static int rq_prio(const struct i915_request *rq)
>   	return rq->sched.attr.priority;
>   }
>   
> +static inline bool is_multi_lrc(struct intel_context *ce)
> +{
> +	return intel_context_is_parallel(ce);
> +}
> +
>   static bool is_multi_lrc_rq(struct i915_request *rq)
>   {
>   	return intel_context_is_parallel(rq->context);
> @@ -1179,10 +1184,13 @@ __unwind_incomplete_requests(struct intel_context *ce)
>   
>   static void __guc_reset_context(struct intel_context *ce, bool stalled)
>   {
> +	bool local_stalled;
>   	struct i915_request *rq;
>   	unsigned long flags;
>   	u32 head;
> +	int i, number_children = ce->guc_number_children;
If this is a child context, does it not need to pull the child count 
from the parent? Likewise the list/link pointers below? Or does each 
child context have a full list of its siblings + parent?

>   	bool skip = false;
> +	struct intel_context *parent = ce;
>   
>   	intel_context_get(ce);
>   
> @@ -1209,25 +1217,34 @@ static void __guc_reset_context(struct intel_context *ce, bool stalled)
>   	if (unlikely(skip))
>   		goto out_put;
>   
> -	rq = intel_context_find_active_request(ce);
> -	if (!rq) {
> -		head = ce->ring->tail;
> -		stalled = false;
> -		goto out_replay;
> -	}
> +	for (i = 0; i < number_children + 1; ++i) {
> +		if (!intel_context_is_pinned(ce))
> +			goto next_context;
> +
> +		local_stalled = false;
> +		rq = intel_context_find_active_request(ce);
> +		if (!rq) {
> +			head = ce->ring->tail;
> +			goto out_replay;
> +		}
>   
> -	if (!i915_request_started(rq))
> -		stalled = false;
> +		GEM_BUG_ON(i915_active_is_idle(&ce->active));
> +		head = intel_ring_wrap(ce->ring, rq->head);
>   
> -	GEM_BUG_ON(i915_active_is_idle(&ce->active));
> -	head = intel_ring_wrap(ce->ring, rq->head);
> -	__i915_request_reset(rq, stalled);
> +		if (i915_request_started(rq))
Why change the ordering of the started test versus the wrap/reset call? 
Is it significant? Why is it now important to be reversed?

> +			local_stalled = true;
>   
> +		__i915_request_reset(rq, local_stalled && stalled);
>   out_replay:
> -	guc_reset_state(ce, head, stalled);
> -	__unwind_incomplete_requests(ce);
> +		guc_reset_state(ce, head, local_stalled && stalled);
> +next_context:
> +		if (i != number_children)
> +			ce = list_next_entry(ce, guc_child_link);
Can this not be put in to the step clause of the for statement?

> +	}
> +
> +	__unwind_incomplete_requests(parent);
>   out_put:
> -	intel_context_put(ce);
> +	intel_context_put(parent);
As above, I think this function would benefit from some comments to 
explain exactly what is being done and why.

John.

>   }
>   
>   void intel_guc_submission_reset(struct intel_guc *guc, bool stalled)
> @@ -1248,7 +1265,8 @@ void intel_guc_submission_reset(struct intel_guc *guc, bool stalled)
>   
>   		xa_unlock(&guc->context_lookup);
>   
> -		if (intel_context_is_pinned(ce))
> +		if (intel_context_is_pinned(ce) &&
> +		    !intel_context_is_child(ce))
>   			__guc_reset_context(ce, stalled);
>   
>   		intel_context_put(ce);
> @@ -1340,7 +1358,8 @@ void intel_guc_submission_cancel_requests(struct intel_guc *guc)
>   
>   		xa_unlock(&guc->context_lookup);
>   
> -		if (intel_context_is_pinned(ce))
> +		if (intel_context_is_pinned(ce) &&
> +		    !intel_context_is_child(ce))
>   			guc_cancel_context_requests(ce);
>   
>   		intel_context_put(ce);
> @@ -2031,6 +2050,8 @@ static struct i915_sw_fence *guc_context_block(struct intel_context *ce)
>   	u16 guc_id;
>   	bool enabled;
>   
> +	GEM_BUG_ON(intel_context_is_child(ce));
> +
>   	spin_lock_irqsave(&ce->guc_state.lock, flags);
>   
>   	incr_context_blocked(ce);
> @@ -2068,6 +2089,7 @@ static void guc_context_unblock(struct intel_context *ce)
>   	bool enable;
>   
>   	GEM_BUG_ON(context_enabled(ce));
> +	GEM_BUG_ON(intel_context_is_child(ce));
>   
>   	spin_lock_irqsave(&ce->guc_state.lock, flags);
>   
> @@ -2099,11 +2121,14 @@ static void guc_context_unblock(struct intel_context *ce)
>   static void guc_context_cancel_request(struct intel_context *ce,
>   				       struct i915_request *rq)
>   {
> +	struct intel_context *block_context =
> +		request_to_scheduling_context(rq);
> +
>   	if (i915_sw_fence_signaled(&rq->submit)) {
>   		struct i915_sw_fence *fence;
>   
>   		intel_context_get(ce);
> -		fence = guc_context_block(ce);
> +		fence = guc_context_block(block_context);
>   		i915_sw_fence_wait(fence);
>   		if (!i915_request_completed(rq)) {
>   			__i915_request_skip(rq);
> @@ -2117,7 +2142,7 @@ static void guc_context_cancel_request(struct intel_context *ce,
>   		 */
>   		flush_work(&ce_to_guc(ce)->ct.requests.worker);
>   
> -		guc_context_unblock(ce);
> +		guc_context_unblock(block_context);
>   		intel_context_put(ce);
>   	}
>   }
> @@ -2143,6 +2168,8 @@ static void guc_context_ban(struct intel_context *ce, struct i915_request *rq)
>   	intel_wakeref_t wakeref;
>   	unsigned long flags;
>   
> +	GEM_BUG_ON(intel_context_is_child(ce));
> +
>   	guc_flush_submissions(guc);
>   
>   	spin_lock_irqsave(&ce->guc_state.lock, flags);


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