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

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

On 10/7/2021 08:05, Matthew Brost wrote:
> On Wed, Oct 06, 2021 at 08:06:41PM -0700, John Harrison wrote:
> > 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.
> Can add that back in.
>
> > > +		/**
> > > +		 * @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?
> It might, not really sure but agree the submission_state should be
> dropped. Think changed because of global find replace.
>
> Matt
Okay. With those nits fixed:
Reviewed by: John Harrison <John.C.Harrison@xxxxxxxxx>

> > 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);