Re: [Intel-gfx] [PATCH 10/26] drm/i915/guc: Assign contexts in parent-child relationship consecutive guc_ids

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

On 10/7/2021 18:21, Matthew Brost wrote:
> On Thu, Oct 07, 2021 at 03:03:04PM -0700, John Harrison wrote:
>> On 10/4/2021 15:06, Matthew Brost wrote:
>>> Assign contexts in parent-child relationship consecutive guc_ids. This
>>> is accomplished by partitioning guc_id space between ones that need to
>>> be consecutive (1/16 available guc_ids) and ones that do not (15/16 of
>>> available guc_ids). The consecutive search is implemented via the bitmap
>>> API.
>>>
>>> This is a precursor to the full GuC multi-lrc implementation but aligns
>>> to how GuC mutli-lrc interface is defined - guc_ids must be consecutive
>>> when using the GuC multi-lrc interface.
>>>
>>> v2:
>>>    (Daniel Vetter)
>>>     - Explicitly state why we assign consecutive guc_ids
>>> v3:
>>>    (John Harrison)
>>>     - Bring back in spin lock
>>>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc.h        |   6 +-
>>>    .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 104 ++++++++++++++----
>>>    2 files changed, 86 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> index 25a598e2b6e8..a9f4ec972bfb 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> @@ -76,9 +76,13 @@ struct intel_guc {
>>>    		 */
>>>    		spinlock_t lock;
>>>    		/**
>>> -		 * @guc_ids: used to allocate new guc_ids
>>> +		 * @guc_ids: used to allocate new guc_ids, single-lrc
>>>    		 */
>>>    		struct ida guc_ids;
>>> +		/**
>>> +		 * @guc_ids_bitmap: used to allocate new guc_ids, multi-lrc
>>> +		 */
>>> +		unsigned long *guc_ids_bitmap;
>>>    		/**
>>>    		 * @guc_id_list: list of intel_context with valid guc_ids but no
>>>    		 * refs
>>> 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 1f2809187513..79e7732e83b2 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -128,6 +128,16 @@ guc_create_virtual(struct intel_engine_cs **siblings, unsigned int count);
>>>    #define GUC_REQUEST_SIZE 64 /* bytes */
>>> +/*
>>> + * We reserve 1/16 of the guc_ids for multi-lrc as these need to be contiguous
>>> + * per the GuC submission interface. A different allocation algorithm is used
>>> + * (bitmap vs. ida) between multi-lrc and single-lrc hence the reason to
>>> + * partition the guc_id space. We believe the number of multi-lrc contexts in
>>> + * use should be low and 1/16 should be sufficient. Minimum of 32 guc_ids for
>>> + * multi-lrc.
>>> + */
>>> +#define NUMBER_MULTI_LRC_GUC_ID		(GUC_MAX_LRC_DESCRIPTORS / 16)
>>> +
>>>    /*
>>>     * Below is a set of functions which control the GuC scheduling state which
>>>     * require a lock.
>>> @@ -1206,6 +1216,11 @@ int intel_guc_submission_init(struct intel_guc *guc)
>>>    	INIT_WORK(&guc->submission_state.destroyed_worker,
>>>    		  destroyed_worker_func);
>>> +	guc->submission_state.guc_ids_bitmap =
>>> +		bitmap_zalloc(NUMBER_MULTI_LRC_GUC_ID, GFP_KERNEL);
>>> +	if (!guc->submission_state.guc_ids_bitmap)
>>> +		return -ENOMEM;
>>> +
>>>    	return 0;
>>>    }
>>> @@ -1217,6 +1232,7 @@ void intel_guc_submission_fini(struct intel_guc *guc)
>>>    	guc_lrc_desc_pool_destroy(guc);
>>>    	guc_flush_destroyed_contexts(guc);
>>>    	i915_sched_engine_put(guc->sched_engine);
>>> +	bitmap_free(guc->submission_state.guc_ids_bitmap);
>>>    }
>>>    static inline void queue_request(struct i915_sched_engine *sched_engine,
>>> @@ -1268,18 +1284,43 @@ static void guc_submit_request(struct i915_request *rq)
>>>    	spin_unlock_irqrestore(&sched_engine->lock, flags);
>>>    }
>>> -static int new_guc_id(struct intel_guc *guc)
>>> +static int new_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    {
>>> -	return ida_simple_get(&guc->submission_state.guc_ids, 0,
>>> -			      GUC_MAX_LRC_DESCRIPTORS, GFP_KERNEL |
>>> -			      __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>>> +	int ret;
>>> +
>>> +	GEM_BUG_ON(intel_context_is_child(ce));
>>> +
>>> +	if (intel_context_is_parent(ce))
>>> +		ret = bitmap_find_free_region(guc->submission_state.guc_ids_bitmap,
>>> +					      NUMBER_MULTI_LRC_GUC_ID,
>>> +					      order_base_2(ce->parallel.number_children
>>> +							   + 1));
>>> +	else
>>> +		ret = ida_simple_get(&guc->submission_state.guc_ids,
>>> +				     NUMBER_MULTI_LRC_GUC_ID,
>>> +				     GUC_MAX_LRC_DESCRIPTORS,
>>> +				     GFP_KERNEL | __GFP_RETRY_MAYFAIL |
>>> +				     __GFP_NOWARN);
>>> +	if (unlikely(ret < 0))
>>> +		return ret;
>>> +
>>> +	ce->guc_id.id = ret;
>>> +	return 0;
>>>    }
>>>    static void __release_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    {
>>> +	GEM_BUG_ON(intel_context_is_child(ce));
>>> +
>>>    	if (!context_guc_id_invalid(ce)) {
>>> -		ida_simple_remove(&guc->submission_state.guc_ids,
>>> -				  ce->guc_id.id);
>>> +		if (intel_context_is_parent(ce))
>>> +			bitmap_release_region(guc->submission_state.guc_ids_bitmap,
>>> +					      ce->guc_id.id,
>>> +					      order_base_2(ce->parallel.number_children
>>> +							   + 1));
>> There was a discussion on the previous revision about adding a BUG_ON to
>> ensure that number_children cannot change between the bitmap alloc and the
>> bitmap release. I'm not seeing the new BUG_ON mentioned in this patch.
>>
> I thought you meant to add a BUG_ON to ensure before we release a region
> / id it is occupied? I looked in both the bitmap API and ida API and
> neither have a function that checks if region / id is occupied so can't
> really add a BUG_ON for that.
>
> How much you add BUG_ON to ensure the number of children canoot change
> between alloc and release? I don't follow how that would work.
>
> Matt
I was thinking that where number_children is modified, you have a 
BUG_ON(guc_id_is_valid). That would ensure that the release has to match 
the alloc. Hmm, you already have a BUG_ON about the parent/child not 
being pinned in intel_context_bind_parent_child(), which I guess covers 
it because you shouldn't have a guc_id if you aren't pinned, right? And 
that is the only function which can modify number_children, yes? So 
maybe it's all good?

John.

>
>> John.
>>
>>
>>> +		else
>>> +			ida_simple_remove(&guc->submission_state.guc_ids,
>>> +					  ce->guc_id.id);
>>>    		reset_lrc_desc(guc, ce->guc_id.id);
>>>    		set_context_guc_id_invalid(ce);
>>>    	}
>>> @@ -1296,49 +1337,64 @@ static void release_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>>    }
>>> -static int steal_guc_id(struct intel_guc *guc)
>>> +static int steal_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    {
>>> -	struct intel_context *ce;
>>> -	int guc_id;
>>> +	struct intel_context *cn;
>>>    	lockdep_assert_held(&guc->submission_state.lock);
>>> +	GEM_BUG_ON(intel_context_is_child(ce));
>>> +	GEM_BUG_ON(intel_context_is_parent(ce));
>>>    	if (!list_empty(&guc->submission_state.guc_id_list)) {
>>> -		ce = list_first_entry(&guc->submission_state.guc_id_list,
>>> +		cn = list_first_entry(&guc->submission_state.guc_id_list,
>>>    				      struct intel_context,
>>>    				      guc_id.link);
>>> -		GEM_BUG_ON(atomic_read(&ce->guc_id.ref));
>>> -		GEM_BUG_ON(context_guc_id_invalid(ce));
>>> +		GEM_BUG_ON(atomic_read(&cn->guc_id.ref));
>>> +		GEM_BUG_ON(context_guc_id_invalid(cn));
>>> +		GEM_BUG_ON(intel_context_is_child(cn));
>>> +		GEM_BUG_ON(intel_context_is_parent(cn));
>>> -		list_del_init(&ce->guc_id.link);
>>> -		guc_id = ce->guc_id.id;
>>> +		list_del_init(&cn->guc_id.link);
>>> +		ce->guc_id = cn->guc_id;
>>>    		spin_lock(&ce->guc_state.lock);
>>> -		clr_context_registered(ce);
>>> +		clr_context_registered(cn);
>>>    		spin_unlock(&ce->guc_state.lock);
>>> -		set_context_guc_id_invalid(ce);
>>> -		return guc_id;
>>> +		set_context_guc_id_invalid(cn);
>>> +
>>> +		return 0;
>>>    	} else {
>>>    		return -EAGAIN;
>>>    	}
>>>    }
>>> -static int assign_guc_id(struct intel_guc *guc, u16 *out)
>>> +static int assign_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    {
>>>    	int ret;
>>>    	lockdep_assert_held(&guc->submission_state.lock);
>>> +	GEM_BUG_ON(intel_context_is_child(ce));
>>> -	ret = new_guc_id(guc);
>>> +	ret = new_guc_id(guc, ce);
>>>    	if (unlikely(ret < 0)) {
>>> -		ret = steal_guc_id(guc);
>>> +		if (intel_context_is_parent(ce))
>>> +			return -ENOSPC;
>>> +
>>> +		ret = steal_guc_id(guc, ce);
>>>    		if (ret < 0)
>>>    			return ret;
>>>    	}
>>> -	*out = ret;
>>> +	if (intel_context_is_parent(ce)) {
>>> +		struct intel_context *child;
>>> +		int i = 1;
>>> +
>>> +		for_each_child(ce, child)
>>> +			child->guc_id.id = ce->guc_id.id + i++;
>>> +	}
>>> +
>>>    	return 0;
>>>    }
>>> @@ -1356,7 +1412,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    	might_lock(&ce->guc_state.lock);
>>>    	if (context_guc_id_invalid(ce)) {
>>> -		ret = assign_guc_id(guc, &ce->guc_id.id);
>>> +		ret = assign_guc_id(guc, ce);
>>>    		if (ret)
>>>    			goto out_unlock;
>>>    		ret = 1;	/* Indidcates newly assigned guc_id */
>>> @@ -1398,8 +1454,10 @@ static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>>    	unsigned long flags;
>>>    	GEM_BUG_ON(atomic_read(&ce->guc_id.ref) < 0);
>>> +	GEM_BUG_ON(intel_context_is_child(ce));
>>> -	if (unlikely(context_guc_id_invalid(ce)))
>>> +	if (unlikely(context_guc_id_invalid(ce) ||
>>> +		     intel_context_is_parent(ce)))
>>>    		return;
>>>    	spin_lock_irqsave(&guc->submission_state.lock, flags);