Re: [PATCH 01/26] drm/i915/guc: Move GuC guc_id allocation under submission state sub-struct

[John Harrison <john.c.harrison@xxxxxxxxx>]

On 10/4/2021 15:06, Matthew Brost wrote:
> Move guc_id allocation under submission state sub-struct as a future
> patch will reuse the spin lock as a global submission state lock. Moving
> this into sub-struct makes ownership of fields / lock clear.
>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gt/intel_context_types.h |  6 +-
>   drivers/gpu/drm/i915/gt/uc/intel_guc.h        | 26 +++++----
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 56 ++++++++++---------
>   3 files changed, 47 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index 12252c411159..e7e3984aab78 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -197,18 +197,18 @@ struct intel_context {
>   	struct {
>   		/**
>   		 * @id: handle which is used to uniquely identify this context
> -		 * with the GuC, protected by guc->contexts_lock
> +		 * with the GuC, protected by guc->submission_state.lock
>   		 */
>   		u16 id;
>   		/**
>   		 * @ref: the number of references to the guc_id, when
>   		 * transitioning in and out of zero protected by
> -		 * guc->contexts_lock
> +		 * guc->submission_state.lock
>   		 */
>   		atomic_t ref;
>   		/**
>   		 * @link: in guc->guc_id_list when the guc_id has no refs but is
> -		 * still valid, protected by guc->contexts_lock
> +		 * still valid, protected by guc->submission_state.lock
>   		 */
>   		struct list_head link;
>   	} guc_id;
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> index 5dd174babf7a..65b5e8eeef96 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> @@ -70,17 +70,21 @@ struct intel_guc {
>   		void (*disable)(struct intel_guc *guc);
>   	} interrupts;
>   
> -	/**
> -	 * @contexts_lock: protects guc_ids, guc_id_list, ce->guc_id.id, and
> -	 * ce->guc_id.ref when transitioning in and out of zero
> -	 */
> -	spinlock_t contexts_lock;
> -	/** @guc_ids: used to allocate unique ce->guc_id.id values */
> -	struct ida guc_ids;
> -	/**
> -	 * @guc_id_list: list of intel_context with valid guc_ids but no refs
> -	 */
> -	struct list_head guc_id_list;
> +	struct {
> +		/**
> +		 * @lock: protects everything in submission_state
> +		 */
> +		spinlock_t lock;
The old version also mentioned 'ce->guc_id.ref'. Should this not also 
mention that transition? Or was the old comment inaccurate. I'm not 
seeing any actual behaviour changes in the patch.


> +		/**
> +		 * @guc_ids: used to allocate new guc_ids
> +		 */
> +		struct ida guc_ids;
> +		/**
> +		 * @guc_id_list: list of intel_context with valid guc_ids but no
> +		 * refs
> +		 */
> +		struct list_head guc_id_list;
> +	} submission_state;
>   
>   	/**
>   	 * @submission_supported: tracks whether we support GuC submission on
> 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 ba0de35f6323..ad5c18119d92 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -68,16 +68,16 @@
>    * fence is used to stall all requests associated with this guc_id until the
>    * corresponding G2H returns indicating the guc_id has been deregistered.
>    *
> - * guc_ids:
> + * submission_state.guc_ids:
>    * Unique number associated with private GuC context data passed in during
>    * context registration / submission / deregistration. 64k available. Simple ida
>    * is used for allocation.
>    *
> - * Stealing guc_ids:
> - * If no guc_ids are available they can be stolen from another context at
> - * request creation time if that context is unpinned. If a guc_id can't be found
> - * we punt this problem to the user as we believe this is near impossible to hit
> - * during normal use cases.
> + * Stealing submission_state.guc_ids:
> + * If no submission_state.guc_ids are available they can be stolen from another
I would abbreviate this instance as well, submission_state.guc_id is 
quite the mouthful. Unless this somehow magically links back to the 
structure entry in the kerneldoc output?

John.

> + * context at request creation time if that context is unpinned. If a guc_id
> + * can't be found we punt this problem to the user as we believe this is near
> + * impossible to hit during normal use cases.
>    *
>    * Locking:
>    * In the GuC submission code we have 3 basic spin locks which protect
> @@ -89,7 +89,7 @@
>    * sched_engine can be submitting at a time. Currently only one sched_engine is
>    * used for all of GuC submission but that could change in the future.
>    *
> - * guc->contexts_lock
> + * guc->submission_state.lock
>    * Protects guc_id allocation for the given GuC, i.e. only one context can be
>    * doing guc_id allocation operations at a time for each GuC in the system.
>    *
> @@ -103,7 +103,7 @@
>    *
>    * Lock ordering rules:
>    * sched_engine->lock -> ce->guc_state.lock
> - * guc->contexts_lock -> ce->guc_state.lock
> + * guc->submission_state.lock -> ce->guc_state.lock
>    *
>    * Reset races:
>    * When a full GT reset is triggered it is assumed that some G2H responses to
> @@ -1148,9 +1148,9 @@ int intel_guc_submission_init(struct intel_guc *guc)
>   
>   	xa_init_flags(&guc->context_lookup, XA_FLAGS_LOCK_IRQ);
>   
> -	spin_lock_init(&guc->contexts_lock);
> -	INIT_LIST_HEAD(&guc->guc_id_list);
> -	ida_init(&guc->guc_ids);
> +	spin_lock_init(&guc->submission_state.lock);
> +	INIT_LIST_HEAD(&guc->submission_state.guc_id_list);
> +	ida_init(&guc->submission_state.guc_ids);
>   
>   	return 0;
>   }
> @@ -1215,7 +1215,7 @@ static void guc_submit_request(struct i915_request *rq)
>   
>   static int new_guc_id(struct intel_guc *guc)
>   {
> -	return ida_simple_get(&guc->guc_ids, 0,
> +	return ida_simple_get(&guc->submission_state.guc_ids, 0,
>   			      GUC_MAX_LRC_DESCRIPTORS, GFP_KERNEL |
>   			      __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>   }
> @@ -1223,7 +1223,8 @@ static int new_guc_id(struct intel_guc *guc)
>   static void __release_guc_id(struct intel_guc *guc, struct intel_context *ce)
>   {
>   	if (!context_guc_id_invalid(ce)) {
> -		ida_simple_remove(&guc->guc_ids, ce->guc_id.id);
> +		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);
>   	}
> @@ -1235,9 +1236,9 @@ static void release_guc_id(struct intel_guc *guc, struct intel_context *ce)
>   {
>   	unsigned long flags;
>   
> -	spin_lock_irqsave(&guc->contexts_lock, flags);
> +	spin_lock_irqsave(&guc->submission_state.lock, flags);
>   	__release_guc_id(guc, ce);
> -	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> +	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>   }
>   
>   static int steal_guc_id(struct intel_guc *guc)
> @@ -1245,10 +1246,10 @@ static int steal_guc_id(struct intel_guc *guc)
>   	struct intel_context *ce;
>   	int guc_id;
>   
> -	lockdep_assert_held(&guc->contexts_lock);
> +	lockdep_assert_held(&guc->submission_state.lock);
>   
> -	if (!list_empty(&guc->guc_id_list)) {
> -		ce = list_first_entry(&guc->guc_id_list,
> +	if (!list_empty(&guc->submission_state.guc_id_list)) {
> +		ce = list_first_entry(&guc->submission_state.guc_id_list,
>   				      struct intel_context,
>   				      guc_id.link);
>   
> @@ -1273,7 +1274,7 @@ static int assign_guc_id(struct intel_guc *guc, u16 *out)
>   {
>   	int ret;
>   
> -	lockdep_assert_held(&guc->contexts_lock);
> +	lockdep_assert_held(&guc->submission_state.lock);
>   
>   	ret = new_guc_id(guc);
>   	if (unlikely(ret < 0)) {
> @@ -1295,7 +1296,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>   	GEM_BUG_ON(atomic_read(&ce->guc_id.ref));
>   
>   try_again:
> -	spin_lock_irqsave(&guc->contexts_lock, flags);
> +	spin_lock_irqsave(&guc->submission_state.lock, flags);
>   
>   	might_lock(&ce->guc_state.lock);
>   
> @@ -1310,7 +1311,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>   	atomic_inc(&ce->guc_id.ref);
>   
>   out_unlock:
> -	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> +	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>   
>   	/*
>   	 * -EAGAIN indicates no guc_id are available, let's retire any
> @@ -1346,11 +1347,12 @@ static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>   	if (unlikely(context_guc_id_invalid(ce)))
>   		return;
>   
> -	spin_lock_irqsave(&guc->contexts_lock, flags);
> +	spin_lock_irqsave(&guc->submission_state.lock, flags);
>   	if (!context_guc_id_invalid(ce) && list_empty(&ce->guc_id.link) &&
>   	    !atomic_read(&ce->guc_id.ref))
> -		list_add_tail(&ce->guc_id.link, &guc->guc_id_list);
> -	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> +		list_add_tail(&ce->guc_id.link,
> +			      &guc->submission_state.guc_id_list);
> +	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>   }
>   
>   static int __guc_action_register_context(struct intel_guc *guc,
> @@ -1921,16 +1923,16 @@ static void guc_context_destroy(struct kref *kref)
>   	 * returns indicating this context has been deregistered the guc_id is
>   	 * returned to the pool of available guc_id.
>   	 */
> -	spin_lock_irqsave(&guc->contexts_lock, flags);
> +	spin_lock_irqsave(&guc->submission_state.lock, flags);
>   	if (context_guc_id_invalid(ce)) {
> -		spin_unlock_irqrestore(&guc->contexts_lock, flags);
> +		spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>   		__guc_context_destroy(ce);
>   		return;
>   	}
>   
>   	if (!list_empty(&ce->guc_id.link))
>   		list_del_init(&ce->guc_id.link);
> -	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> +	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>   
>   	/* Seal race with Reset */
>   	spin_lock_irqsave(&ce->guc_state.lock, flags);