Re: [Intel-gfx] [PATCH 20/27] drm/i915/guc: Rework and simplify locking

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On Wed, Aug 25, 2021 at 09:52:06AM -0700, Daniele Ceraolo Spurio wrote:
> 
> 
> On 8/18/2021 11:16 PM, Matthew Brost wrote:
> > Rework and simplify the locking with GuC subission. Drop
> > sched_state_no_lock and move all fields under the guc_state.sched_state
> > and protect all these fields with guc_state.lock . This requires
> > changing the locking hierarchy from guc_state.lock -> sched_engine.lock
> > to sched_engine.lock -> guc_state.lock.
> > 
> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_context_types.h |   5 +-
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 186 ++++++++----------
> >   drivers/gpu/drm/i915/i915_trace.h             |   6 +-
> >   3 files changed, 89 insertions(+), 108 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> > index c06171ee8792..d5d643b04d54 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> > @@ -161,7 +161,7 @@ struct intel_context {
> >   		 * sched_state: scheduling state of this context using GuC
> >   		 * submission
> >   		 */
> > -		u16 sched_state;
> > +		u32 sched_state;
> >   		/*
> >   		 * fences: maintains of list of requests that have a submit
> >   		 * fence related to GuC submission
> > @@ -178,9 +178,6 @@ struct intel_context {
> >   		struct list_head requests;
> >   	} guc_active;
> > -	/* GuC scheduling state flags that do not require a lock. */
> > -	atomic_t guc_sched_state_no_lock;
> > -
> >   	/* GuC LRC descriptor ID */
> >   	u16 guc_id;
> > 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 053f4485d6e9..509b298e7cf3 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -72,86 +72,23 @@ guc_create_virtual(struct intel_engine_cs **siblings, unsigned int count);
> >   #define GUC_REQUEST_SIZE 64 /* bytes */
> > -/*
> > - * Below is a set of functions which control the GuC scheduling state which do
> > - * not require a lock as all state transitions are mutually exclusive. i.e. It
> > - * is not possible for the context pinning code and submission, for the same
> > - * context, to be executing simultaneously. We still need an atomic as it is
> > - * possible for some of the bits to changing at the same time though.
> > - */
> > -#define SCHED_STATE_NO_LOCK_ENABLED			BIT(0)
> > -#define SCHED_STATE_NO_LOCK_PENDING_ENABLE		BIT(1)
> > -#define SCHED_STATE_NO_LOCK_REGISTERED			BIT(2)
> > -static inline bool context_enabled(struct intel_context *ce)
> > -{
> > -	return (atomic_read(&ce->guc_sched_state_no_lock) &
> > -		SCHED_STATE_NO_LOCK_ENABLED);
> > -}
> > -
> > -static inline void set_context_enabled(struct intel_context *ce)
> > -{
> > -	atomic_or(SCHED_STATE_NO_LOCK_ENABLED, &ce->guc_sched_state_no_lock);
> > -}
> > -
> > -static inline void clr_context_enabled(struct intel_context *ce)
> > -{
> > -	atomic_and((u32)~SCHED_STATE_NO_LOCK_ENABLED,
> > -		   &ce->guc_sched_state_no_lock);
> > -}
> > -
> > -static inline bool context_pending_enable(struct intel_context *ce)
> > -{
> > -	return (atomic_read(&ce->guc_sched_state_no_lock) &
> > -		SCHED_STATE_NO_LOCK_PENDING_ENABLE);
> > -}
> > -
> > -static inline void set_context_pending_enable(struct intel_context *ce)
> > -{
> > -	atomic_or(SCHED_STATE_NO_LOCK_PENDING_ENABLE,
> > -		  &ce->guc_sched_state_no_lock);
> > -}
> > -
> > -static inline void clr_context_pending_enable(struct intel_context *ce)
> > -{
> > -	atomic_and((u32)~SCHED_STATE_NO_LOCK_PENDING_ENABLE,
> > -		   &ce->guc_sched_state_no_lock);
> > -}
> > -
> > -static inline bool context_registered(struct intel_context *ce)
> > -{
> > -	return (atomic_read(&ce->guc_sched_state_no_lock) &
> > -		SCHED_STATE_NO_LOCK_REGISTERED);
> > -}
> > -
> > -static inline void set_context_registered(struct intel_context *ce)
> > -{
> > -	atomic_or(SCHED_STATE_NO_LOCK_REGISTERED,
> > -		  &ce->guc_sched_state_no_lock);
> > -}
> > -
> > -static inline void clr_context_registered(struct intel_context *ce)
> > -{
> > -	atomic_and((u32)~SCHED_STATE_NO_LOCK_REGISTERED,
> > -		   &ce->guc_sched_state_no_lock);
> > -}
> > -
> >   /*
> >    * Below is a set of functions which control the GuC scheduling state which
> > - * require a lock, aside from the special case where the functions are called
> > - * from guc_lrc_desc_pin(). In that case it isn't possible for any other code
> > - * path to be executing on the context.
> > + * require a lock.
> >    */
> >   #define SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER	BIT(0)
> >   #define SCHED_STATE_DESTROYED				BIT(1)
> >   #define SCHED_STATE_PENDING_DISABLE			BIT(2)
> >   #define SCHED_STATE_BANNED				BIT(3)
> > -#define SCHED_STATE_BLOCKED_SHIFT			4
> > +#define SCHED_STATE_ENABLED				BIT(4)
> > +#define SCHED_STATE_PENDING_ENABLE			BIT(5)
> > +#define SCHED_STATE_REGISTERED				BIT(6)
> > +#define SCHED_STATE_BLOCKED_SHIFT			7
> >   #define SCHED_STATE_BLOCKED		BIT(SCHED_STATE_BLOCKED_SHIFT)
> >   #define SCHED_STATE_BLOCKED_MASK	(0xfff << SCHED_STATE_BLOCKED_SHIFT)
> >   static inline void init_sched_state(struct intel_context *ce)
> >   {
> >   	lockdep_assert_held(&ce->guc_state.lock);
> > -	atomic_set(&ce->guc_sched_state_no_lock, 0);
> >   	ce->guc_state.sched_state &= SCHED_STATE_BLOCKED_MASK;
> >   }
> > @@ -162,9 +99,8 @@ static bool sched_state_is_init(struct intel_context *ce)
> >   	 * XXX: Kernel contexts can have SCHED_STATE_NO_LOCK_REGISTERED after
> >   	 * suspend.
> >   	 */
> > -	return !(atomic_read(&ce->guc_sched_state_no_lock) &
> > -		 ~SCHED_STATE_NO_LOCK_REGISTERED) &&
> > -		!(ce->guc_state.sched_state &= ~SCHED_STATE_BLOCKED_MASK);
> > +	return !(ce->guc_state.sched_state &=
> > +		 ~(SCHED_STATE_BLOCKED_MASK | SCHED_STATE_REGISTERED));
> >   }
> >   static inline bool
> > @@ -237,6 +173,57 @@ static inline void clr_context_banned(struct intel_context *ce)
> >   	ce->guc_state.sched_state &= ~SCHED_STATE_BANNED;
> >   }
> > +static inline bool context_enabled(struct intel_context *ce)
> > +{
> > +	return ce->guc_state.sched_state & SCHED_STATE_ENABLED;
> > +}
> > +
> > +static inline void set_context_enabled(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state |= SCHED_STATE_ENABLED;
> > +}
> > +
> > +static inline void clr_context_enabled(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state &= ~SCHED_STATE_ENABLED;
> > +}
> > +
> > +static inline bool context_pending_enable(struct intel_context *ce)
> > +{
> > +	return ce->guc_state.sched_state & SCHED_STATE_PENDING_ENABLE;
> > +}
> > +
> > +static inline void set_context_pending_enable(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state |= SCHED_STATE_PENDING_ENABLE;
> > +}
> > +
> > +static inline void clr_context_pending_enable(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state &= ~SCHED_STATE_PENDING_ENABLE;
> > +}
> > +
> > +static inline bool context_registered(struct intel_context *ce)
> > +{
> > +	return ce->guc_state.sched_state & SCHED_STATE_REGISTERED;
> > +}
> > +
> > +static inline void set_context_registered(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state |= SCHED_STATE_REGISTERED;
> > +}
> > +
> > +static inline void clr_context_registered(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state &= ~SCHED_STATE_REGISTERED;
> > +}
> > +
> >   static inline u32 context_blocked(struct intel_context *ce)
> >   {
> >   	return (ce->guc_state.sched_state & SCHED_STATE_BLOCKED_MASK) >>
> > @@ -245,7 +232,6 @@ static inline u32 context_blocked(struct intel_context *ce)
> >   static inline void incr_context_blocked(struct intel_context *ce)
> >   {
> > -	lockdep_assert_held(&ce->engine->sched_engine->lock);
> >   	lockdep_assert_held(&ce->guc_state.lock);
> >   	ce->guc_state.sched_state += SCHED_STATE_BLOCKED;
> > @@ -255,7 +241,6 @@ static inline void incr_context_blocked(struct intel_context *ce)
> >   static inline void decr_context_blocked(struct intel_context *ce)
> >   {
> > -	lockdep_assert_held(&ce->engine->sched_engine->lock);
> >   	lockdep_assert_held(&ce->guc_state.lock);
> >   	GEM_BUG_ON(!context_blocked(ce));	/* Underflow check */
> > @@ -450,6 +435,8 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
> >   	u32 g2h_len_dw = 0;
> >   	bool enabled;
> > +	lockdep_assert_held(&rq->engine->sched_engine->lock);
> > +
> >   	/*
> >   	 * Corner case where requests were sitting in the priority list or a
> >   	 * request resubmitted after the context was banned.
> > @@ -457,7 +444,7 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
> >   	if (unlikely(intel_context_is_banned(ce))) {
> >   		i915_request_put(i915_request_mark_eio(rq));
> >   		intel_engine_signal_breadcrumbs(ce->engine);
> > -		goto out;
> > +		return 0;
> >   	}
> >   	GEM_BUG_ON(!atomic_read(&ce->guc_id_ref));
> > @@ -470,9 +457,11 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
> >   	if (unlikely(!lrc_desc_registered(guc, ce->guc_id))) {
> >   		err = guc_lrc_desc_pin(ce, false);
> >   		if (unlikely(err))
> > -			goto out;
> > +			return err;
> >   	}
> > +	spin_lock(&ce->guc_state.lock);
> > +
> >   	/*
> >   	 * The request / context will be run on the hardware when scheduling
> >   	 * gets enabled in the unblock.
> > @@ -507,6 +496,7 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
> >   		trace_i915_request_guc_submit(rq);
> >   out:
> > +	spin_unlock(&ce->guc_state.lock);
> >   	return err;
> >   }
> > @@ -727,8 +717,6 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
> >   	spin_lock_irq(&guc_to_gt(guc)->irq_lock);
> >   	spin_unlock_irq(&guc_to_gt(guc)->irq_lock);
> > -	guc_flush_submissions(guc);
> > -
> >   	flush_work(&guc->ct.requests.worker);
> >   	scrub_guc_desc_for_outstanding_g2h(guc);
> > @@ -1133,7 +1121,11 @@ static int steal_guc_id(struct intel_guc *guc)
> >   		list_del_init(&ce->guc_id_link);
> >   		guc_id = ce->guc_id;
> > +
> > +		spin_lock(&ce->guc_state.lock);
> >   		clr_context_registered(ce);
> > +		spin_unlock(&ce->guc_state.lock);
> > +
> >   		set_context_guc_id_invalid(ce);
> >   		return guc_id;
> >   	} else {
> > @@ -1169,6 +1161,8 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
> >   try_again:
> >   	spin_lock_irqsave(&guc->contexts_lock, flags);
> > +	might_lock(&ce->guc_state.lock);
> > +
> >   	if (context_guc_id_invalid(ce)) {
> >   		ret = assign_guc_id(guc, &ce->guc_id);
> >   		if (ret)
> > @@ -1248,8 +1242,13 @@ static int register_context(struct intel_context *ce, bool loop)
> >   	trace_intel_context_register(ce);
> >   	ret = __guc_action_register_context(guc, ce->guc_id, offset, loop);
> > -	if (likely(!ret))
> > +	if (likely(!ret)) {
> > +		unsigned long flags;
> > +
> > +		spin_lock_irqsave(&ce->guc_state.lock, flags);
> >   		set_context_registered(ce);
> > +		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > +	}
> >   	return ret;
> >   }
> > @@ -1525,7 +1524,6 @@ static u16 prep_context_pending_disable(struct intel_context *ce)
> >   static struct i915_sw_fence *guc_context_block(struct intel_context *ce)
> >   {
> >   	struct intel_guc *guc = ce_to_guc(ce);
> > -	struct i915_sched_engine *sched_engine = ce->engine->sched_engine;
> >   	unsigned long flags;
> >   	struct intel_runtime_pm *runtime_pm = ce->engine->uncore->rpm;
> >   	intel_wakeref_t wakeref;
> > @@ -1534,13 +1532,7 @@ static struct i915_sw_fence *guc_context_block(struct intel_context *ce)
> >   	spin_lock_irqsave(&ce->guc_state.lock, flags);
> > -	/*
> > -	 * Sync with submission path, increment before below changes to context
> > -	 * state.
> > -	 */
> > -	spin_lock(&sched_engine->lock);
> >   	incr_context_blocked(ce);
> > -	spin_unlock(&sched_engine->lock);
> >   	enabled = context_enabled(ce);
> >   	if (unlikely(!enabled || submission_disabled(guc))) {
> > @@ -1569,7 +1561,6 @@ static struct i915_sw_fence *guc_context_block(struct intel_context *ce)
> >   static void guc_context_unblock(struct intel_context *ce)
> >   {
> >   	struct intel_guc *guc = ce_to_guc(ce);
> > -	struct i915_sched_engine *sched_engine = ce->engine->sched_engine;
> >   	unsigned long flags;
> >   	struct intel_runtime_pm *runtime_pm = ce->engine->uncore->rpm;
> >   	intel_wakeref_t wakeref;
> > @@ -1594,13 +1585,7 @@ static void guc_context_unblock(struct intel_context *ce)
> >   		intel_context_get(ce);
> >   	}
> > -	/*
> > -	 * Sync with submission path, decrement after above changes to context
> > -	 * state.
> > -	 */
> > -	spin_lock(&sched_engine->lock);
> >   	decr_context_blocked(ce);
> > -	spin_unlock(&sched_engine->lock);
> >   	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > @@ -1710,7 +1695,9 @@ static void guc_context_sched_disable(struct intel_context *ce)
> >   	if (submission_disabled(guc) || context_guc_id_invalid(ce) ||
> >   	    !lrc_desc_registered(guc, ce->guc_id)) {
> > +		spin_lock_irqsave(&ce->guc_state.lock, flags);
> 
> We do take this lock a few lines below this. Would it be worth just moving
> that up and do everything under the lock?
> 

Good catch. Yes, we should move everything under the which actually
makes all of this code quite a bit simpler too. Will fix.

Matt

> Anyway, all calls to the updated set/clr functions have been updated to be
> correctly locked, so:
> 
> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> 
> Daniele
> 
> >   		clr_context_enabled(ce);
> > +		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> >   		goto unpin;
> >   	}
> > @@ -1760,7 +1747,6 @@ static inline void guc_lrc_desc_unpin(struct intel_context *ce)
> >   	GEM_BUG_ON(ce != __get_context(guc, ce->guc_id));
> >   	GEM_BUG_ON(context_enabled(ce));
> > -	clr_context_registered(ce);
> >   	deregister_context(ce, ce->guc_id, true);
> >   }
> > @@ -1833,8 +1819,10 @@ static void guc_context_destroy(struct kref *kref)
> >   	/* Seal race with Reset */
> >   	spin_lock_irqsave(&ce->guc_state.lock, flags);
> >   	disabled = submission_disabled(guc);
> > -	if (likely(!disabled))
> > +	if (likely(!disabled)) {
> >   		set_context_destroyed(ce);
> > +		clr_context_registered(ce);
> > +	}
> >   	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> >   	if (unlikely(disabled)) {
> >   		release_guc_id(guc, ce);
> > @@ -2697,8 +2685,7 @@ int intel_guc_sched_done_process_msg(struct intel_guc *guc,
> >   		     (!context_pending_enable(ce) &&
> >   		     !context_pending_disable(ce)))) {
> >   		drm_err(&guc_to_gt(guc)->i915->drm,
> > -			"Bad context sched_state 0x%x, 0x%x, desc_idx %u",
> > -			atomic_read(&ce->guc_sched_state_no_lock),
> > +			"Bad context sched_state 0x%x, desc_idx %u",
> >   			ce->guc_state.sched_state, desc_idx);
> >   		return -EPROTO;
> >   	}
> > @@ -2713,7 +2700,9 @@ int intel_guc_sched_done_process_msg(struct intel_guc *guc,
> >   		}
> >   #endif
> > +		spin_lock_irqsave(&ce->guc_state.lock, flags);
> >   		clr_context_pending_enable(ce);
> > +		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> >   	} else if (context_pending_disable(ce)) {
> >   		bool banned;
> > @@ -2987,9 +2976,8 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
> >   			   atomic_read(&ce->pin_count));
> >   		drm_printf(p, "\t\tGuC ID Ref Count: %u\n",
> >   			   atomic_read(&ce->guc_id_ref));
> > -		drm_printf(p, "\t\tSchedule State: 0x%x, 0x%x\n\n",
> > -			   ce->guc_state.sched_state,
> > -			   atomic_read(&ce->guc_sched_state_no_lock));
> > +		drm_printf(p, "\t\tSchedule State: 0x%x\n\n",
> > +			   ce->guc_state.sched_state);
> >   		guc_log_context_priority(p, ce);
> >   	}
> > diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
> > index 806ad688274b..0a77eb2944b5 100644
> > --- a/drivers/gpu/drm/i915/i915_trace.h
> > +++ b/drivers/gpu/drm/i915/i915_trace.h
> > @@ -903,7 +903,6 @@ DECLARE_EVENT_CLASS(intel_context,
> >   			     __field(u32, guc_id)
> >   			     __field(int, pin_count)
> >   			     __field(u32, sched_state)
> > -			     __field(u32, guc_sched_state_no_lock)
> >   			     __field(u8, guc_prio)
> >   			     ),
> > @@ -911,15 +910,12 @@ DECLARE_EVENT_CLASS(intel_context,
> >   			   __entry->guc_id = ce->guc_id;
> >   			   __entry->pin_count = atomic_read(&ce->pin_count);
> >   			   __entry->sched_state = ce->guc_state.sched_state;
> > -			   __entry->guc_sched_state_no_lock =
> > -			   atomic_read(&ce->guc_sched_state_no_lock);
> >   			   __entry->guc_prio = ce->guc_prio;
> >   			   ),
> > -		    TP_printk("guc_id=%d, pin_count=%d sched_state=0x%x,0x%x, guc_prio=%u",
> > +		    TP_printk("guc_id=%d, pin_count=%d sched_state=0x%x, guc_prio=%u",
> >   			      __entry->guc_id, __entry->pin_count,
> >   			      __entry->sched_state,
> > -			      __entry->guc_sched_state_no_lock,
> >   			      __entry->guc_prio)
> >   );
> 



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