Re: [PATCH 15/47] drm/i915/guc: Defer context unpin until scheduling is disabled

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

On 6/24/2021 00:04, Matthew Brost wrote:
> With GuC scheduling, it isn't safe to unpin a context while scheduling
> is enabled for that context as the GuC may touch some of the pinned
> state (e.g. LRC). To ensure scheduling isn't enabled when an unpin is
> done, a call back is added to intel_context_unpin when pin count == 1
> to disable scheduling for that context. When the response CTB is
> received it is safe to do the final unpin.
>
> Future patches may add a heuristic / delay to schedule the disable
> call back to avoid thrashing on schedule enable / disable.
>
> Cc: John Harrison <john.c.harrison@xxxxxxxxx>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
Reviewed-by: John Harrison <John.C.Harrison@xxxxxxxxx>

> ---
>   drivers/gpu/drm/i915/gt/intel_context.c       |   4 +-
>   drivers/gpu/drm/i915/gt/intel_context.h       |  27 +++-
>   drivers/gpu/drm/i915/gt/intel_context_types.h |   2 +
>   drivers/gpu/drm/i915/gt/uc/intel_guc.h        |   2 +
>   drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c     |   3 +
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 145 +++++++++++++++++-
>   6 files changed, 179 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index f750c826e19d..1499b8aace2a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -306,9 +306,9 @@ int __intel_context_do_pin(struct intel_context *ce)
>   	return err;
>   }
>   
> -void intel_context_unpin(struct intel_context *ce)
> +void __intel_context_do_unpin(struct intel_context *ce, int sub)
>   {
> -	if (!atomic_dec_and_test(&ce->pin_count))
> +	if (!atomic_sub_and_test(sub, &ce->pin_count))
>   		return;
>   
>   	CE_TRACE(ce, "unpin\n");
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
> index f83a73a2b39f..8a7199afbe61 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context.h
> @@ -113,7 +113,32 @@ static inline void __intel_context_pin(struct intel_context *ce)
>   	atomic_inc(&ce->pin_count);
>   }
>   
> -void intel_context_unpin(struct intel_context *ce);
> +void __intel_context_do_unpin(struct intel_context *ce, int sub);
> +
> +static inline void intel_context_sched_disable_unpin(struct intel_context *ce)
> +{
> +	__intel_context_do_unpin(ce, 2);
> +}
> +
> +static inline void intel_context_unpin(struct intel_context *ce)
> +{
> +	if (!ce->ops->sched_disable) {
> +		__intel_context_do_unpin(ce, 1);
> +	} else {
> +		/*
> +		 * Move ownership of this pin to the scheduling disable which is
> +		 * an async operation. When that operation completes the above
> +		 * intel_context_sched_disable_unpin is called potentially
> +		 * unpinning the context.
> +		 */
> +		while (!atomic_add_unless(&ce->pin_count, -1, 1)) {
> +			if (atomic_cmpxchg(&ce->pin_count, 1, 2) == 1) {
> +				ce->ops->sched_disable(ce);
> +				break;
> +			}
> +		}
> +	}
> +}
>   
>   void intel_context_enter_engine(struct intel_context *ce);
>   void intel_context_exit_engine(struct intel_context *ce);
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index beafe55a9101..e7af6a2368f8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -43,6 +43,8 @@ struct intel_context_ops {
>   	void (*enter)(struct intel_context *ce);
>   	void (*exit)(struct intel_context *ce);
>   
> +	void (*sched_disable)(struct intel_context *ce);
> +
>   	void (*reset)(struct intel_context *ce);
>   	void (*destroy)(struct kref *kref);
>   };
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> index d44316dc914b..b43ec56986b5 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> @@ -236,6 +236,8 @@ int intel_guc_reset_engine(struct intel_guc *guc,
>   
>   int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
>   					  const u32 *msg, u32 len);
> +int intel_guc_sched_done_process_msg(struct intel_guc *guc,
> +				     const u32 *msg, u32 len);
>   
>   void intel_guc_load_status(struct intel_guc *guc, struct drm_printer *p);
>   
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> index 42a7daef2ff6..7491f041859e 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> @@ -905,6 +905,9 @@ static int ct_process_request(struct intel_guc_ct *ct, struct ct_incoming_msg *r
>   		ret = intel_guc_deregister_done_process_msg(guc, payload,
>   							    len);
>   		break;
> +	case INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_DONE:
> +		ret = intel_guc_sched_done_process_msg(guc, payload, len);
> +		break;
>   	default:
>   		ret = -EOPNOTSUPP;
>   		break;
> 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 49e5d460d54b..0386ccd5a481 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -70,6 +70,7 @@
>    * 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)
>   static inline bool context_enabled(struct intel_context *ce)
>   {
>   	return (atomic_read(&ce->guc_sched_state_no_lock) &
> @@ -87,6 +88,24 @@ static inline void clr_context_enabled(struct intel_context *ce)
>   		   &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);
> +}
> +
>   /*
>    * 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
> @@ -95,6 +114,7 @@ static inline void clr_context_enabled(struct intel_context *ce)
>    */
>   #define SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER	BIT(0)
>   #define SCHED_STATE_DESTROYED				BIT(1)
> +#define SCHED_STATE_PENDING_DISABLE			BIT(2)
>   static inline void init_sched_state(struct intel_context *ce)
>   {
>   	/* Only should be called from guc_lrc_desc_pin() */
> @@ -139,6 +159,24 @@ set_context_destroyed(struct intel_context *ce)
>   	ce->guc_state.sched_state |= SCHED_STATE_DESTROYED;
>   }
>   
> +static inline bool context_pending_disable(struct intel_context *ce)
> +{
> +	return (ce->guc_state.sched_state & SCHED_STATE_PENDING_DISABLE);
> +}
> +
> +static inline void set_context_pending_disable(struct intel_context *ce)
> +{
> +	lockdep_assert_held(&ce->guc_state.lock);
> +	ce->guc_state.sched_state |= SCHED_STATE_PENDING_DISABLE;
> +}
> +
> +static inline void clr_context_pending_disable(struct intel_context *ce)
> +{
> +	lockdep_assert_held(&ce->guc_state.lock);
> +	ce->guc_state.sched_state =
> +		(ce->guc_state.sched_state & ~SCHED_STATE_PENDING_DISABLE);
> +}
> +
>   static inline bool context_guc_id_invalid(struct intel_context *ce)
>   {
>   	return (ce->guc_id == GUC_INVALID_LRC_ID);
> @@ -231,6 +269,8 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>   		action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_SET;
>   		action[len++] = ce->guc_id;
>   		action[len++] = GUC_CONTEXT_ENABLE;
> +		set_context_pending_enable(ce);
> +		intel_context_get(ce);
>   	} else {
>   		action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT;
>   		action[len++] = ce->guc_id;
> @@ -238,8 +278,12 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>   
>   	err = intel_guc_send_nb(guc, action, len);
>   
> -	if (!enabled && !err)
> +	if (!enabled && !err) {
>   		set_context_enabled(ce);
> +	} else if (!enabled) {
> +		clr_context_pending_enable(ce);
> +		intel_context_put(ce);
> +	}
>   
>   	return err;
>   }
> @@ -831,6 +875,60 @@ static void guc_context_post_unpin(struct intel_context *ce)
>   	lrc_post_unpin(ce);
>   }
>   
> +static void __guc_context_sched_disable(struct intel_guc *guc,
> +					struct intel_context *ce,
> +					u16 guc_id)
> +{
> +	u32 action[] = {
> +		INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_SET,
> +		guc_id,	/* ce->guc_id not stable */
> +		GUC_CONTEXT_DISABLE
> +	};
> +
> +	GEM_BUG_ON(guc_id == GUC_INVALID_LRC_ID);
> +
> +	intel_context_get(ce);
> +
> +	intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
> +}
> +
> +static u16 prep_context_pending_disable(struct intel_context *ce)
> +{
> +	set_context_pending_disable(ce);
> +	clr_context_enabled(ce);
> +
> +	return ce->guc_id;
> +}
> +
> +static void guc_context_sched_disable(struct intel_context *ce)
> +{
> +	struct intel_guc *guc = ce_to_guc(ce);
> +	struct intel_runtime_pm *runtime_pm = &ce->engine->gt->i915->runtime_pm;
> +	unsigned long flags;
> +	u16 guc_id;
> +	intel_wakeref_t wakeref;
> +
> +	if (context_guc_id_invalid(ce) ||
> +	    !lrc_desc_registered(guc, ce->guc_id)) {
> +		clr_context_enabled(ce);
> +		goto unpin;
> +	}
> +
> +	if (!context_enabled(ce))
> +		goto unpin;
> +
> +	spin_lock_irqsave(&ce->guc_state.lock, flags);
> +	guc_id = prep_context_pending_disable(ce);
> +	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> +
> +	with_intel_runtime_pm(runtime_pm, wakeref)
> +		__guc_context_sched_disable(guc, ce, guc_id);
> +
> +	return;
> +unpin:
> +	intel_context_sched_disable_unpin(ce);
> +}
> +
>   static inline void guc_lrc_desc_unpin(struct intel_context *ce)
>   {
>   	struct intel_engine_cs *engine = ce->engine;
> @@ -839,6 +937,7 @@ static inline void guc_lrc_desc_unpin(struct intel_context *ce)
>   
>   	GEM_BUG_ON(!lrc_desc_registered(guc, ce->guc_id));
>   	GEM_BUG_ON(ce != __get_context(guc, ce->guc_id));
> +	GEM_BUG_ON(context_enabled(ce));
>   
>   	spin_lock_irqsave(&ce->guc_state.lock, flags);
>   	set_context_destroyed(ce);
> @@ -920,6 +1019,8 @@ static const struct intel_context_ops guc_context_ops = {
>   	.enter = intel_context_enter_engine,
>   	.exit = intel_context_exit_engine,
>   
> +	.sched_disable = guc_context_sched_disable,
> +
>   	.reset = lrc_reset,
>   	.destroy = guc_context_destroy,
>   };
> @@ -1352,3 +1453,45 @@ int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
>   
>   	return 0;
>   }
> +
> +int intel_guc_sched_done_process_msg(struct intel_guc *guc,
> +				     const u32 *msg,
> +				     u32 len)
> +{
> +	struct intel_context *ce;
> +	unsigned long flags;
> +	u32 desc_idx = msg[0];
> +
> +	if (unlikely(len < 2)) {
> +		drm_dbg(&guc_to_gt(guc)->i915->drm, "Invalid length %u", len);
> +		return -EPROTO;
> +	}
> +
> +	ce = g2h_context_lookup(guc, desc_idx);
> +	if (unlikely(!ce))
> +		return -EPROTO;
> +
> +	if (unlikely(context_destroyed(ce) ||
> +		     (!context_pending_enable(ce) &&
> +		     !context_pending_disable(ce)))) {
> +		drm_dbg(&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),
> +			ce->guc_state.sched_state, desc_idx);
> +		return -EPROTO;
> +	}
> +
> +	if (context_pending_enable(ce)) {
> +		clr_context_pending_enable(ce);
> +	} else if (context_pending_disable(ce)) {
> +		intel_context_sched_disable_unpin(ce);
> +
> +		spin_lock_irqsave(&ce->guc_state.lock, flags);
> +		clr_context_pending_disable(ce);
> +		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> +	}
> +
> +	intel_context_put(ce);
> +
> +	return 0;
> +}

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