Re: [PATCH] drm/i915/pmu: Connect engine busyness stats from GuC to pmu

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

On 06/10/2021 00:14, Matthew Brost wrote:
> On Tue, Oct 05, 2021 at 10:47:11AM -0700, Umesh Nerlige Ramappa wrote:
> > With GuC handling scheduling, i915 is not aware of the time that a
> > context is scheduled in and out of the engine. Since i915 pmu relies on
> > this info to provide engine busyness to the user, GuC shares this info
> > with i915 for all engines using shared memory. For each engine, this
> > info contains:
> >
> > - total busyness: total time that the context was running (total)
> > - id: id of the running context (id)
> > - start timestamp: timestamp when the context started running (start)
> >
> > At the time (now) of sampling the engine busyness, if the id is valid
> > (!= ~0), and start is non-zero, then the context is considered to be
> > active and the engine busyness is calculated using the below equation
> >
> > 	engine busyness = total + (now - start)
> >
> > All times are obtained from the gt clock base. For inactive contexts,
> > engine busyness is just equal to the total.
> >
> > The start and total values provided by GuC are 32 bits and wrap around
> > in a few minutes. Since perf pmu provides busyness as 64 bit
> > monotonically increasing values, there is a need for this implementation
> > to account for overflows and extend the time to 64 bits before returning
> > busyness to the user. In order to do that, a worker runs periodically at
> > frequency = 1/8th the time it takes for the timestamp to wrap. As an
> > example, that would be once in 27 seconds for a gt clock frequency of
> > 19.2 MHz.
> >
> > Opens and wip that are targeted for later patches:
> >
> > 1) On global gt reset the total busyness of engines resets and i915
> >     needs to fix that so that user sees monotonically increasing
> >     busyness.
> > 2) In runtime suspend mode, the worker may not need to be run. We could
> >     stop the worker on suspend and rerun it on resume provided that the
> >     guc pm timestamp does not tick during suspend.
> >
> > Note:
> > There might be an overaccounting of busyness due to the fact that GuC
> > may be updating the total and start values while kmd is reading them.
> > (i.e kmd may read the updated total and the stale start). In such a
> > case, user may see higher busyness value followed by smaller ones which
> > would eventually catch up to the higher value.
> >
> > v2: (Tvrtko)
> > - Include details in commit message
> > - Move intel engine busyness function into execlist code
> > - Use union inside engine->stats
> > - Use natural type for ping delay jiffies
> > - Drop active_work condition checks
> > - Use for_each_engine if iterating all engines
> > - Drop seq locking, use spinlock at guc level to update engine stats
> > - Document worker specific details
> >
> > v3: (Tvrtko/Umesh)
> > - Demarcate guc and execlist stat objects with comments
> > - Document known over-accounting issue in commit
> > - Provide a consistent view of guc state
> > - Add hooks to gt park/unpark for guc busyness
> > - Stop/start worker in gt park/unpark path
> > - Drop inline
> > - Move spinlock and worker inits to guc initialization
> > - Drop helpers that are called only once
> >
> > Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> > Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_engine_cs.c     |  26 +-
> >   drivers/gpu/drm/i915/gt/intel_engine_types.h  |  90 +++++--
> >   .../drm/i915/gt/intel_execlists_submission.c  |  32 +++
> >   drivers/gpu/drm/i915/gt/intel_gt_pm.c         |   2 +
> >   .../gpu/drm/i915/gt/uc/abi/guc_actions_abi.h  |   1 +
> >   drivers/gpu/drm/i915/gt/uc/intel_guc.h        |  26 ++
> >   drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c    |  21 ++
> >   drivers/gpu/drm/i915/gt/uc/intel_guc_ads.h    |   5 +
> >   drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h   |  13 +
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 227 ++++++++++++++++++
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.h |   2 +
> >   drivers/gpu/drm/i915/i915_reg.h               |   2 +
> >   12 files changed, 398 insertions(+), 49 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > index 2ae57e4656a3..6fcc70a313d9 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > @@ -1873,22 +1873,6 @@ void intel_engine_dump(struct intel_engine_cs *engine,
> >   	intel_engine_print_breadcrumbs(engine, m);
> >   }
> >   
> > -static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine,
> > -					    ktime_t *now)
> > -{
> > -	ktime_t total = engine->stats.total;
> > -
> > -	/*
> > -	 * If the engine is executing something at the moment
> > -	 * add it to the total.
> > -	 */
> > -	*now = ktime_get();
> > -	if (READ_ONCE(engine->stats.active))
> > -		total = ktime_add(total, ktime_sub(*now, engine->stats.start));
> > -
> > -	return total;
> > -}
> > -
> >   /**
> >    * intel_engine_get_busy_time() - Return current accumulated engine busyness
> >    * @engine: engine to report on
> > @@ -1898,15 +1882,7 @@ static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine,
> >    */
> >   ktime_t intel_engine_get_busy_time(struct intel_engine_cs *engine, ktime_t *now)
> >   {
> > -	unsigned int seq;
> > -	ktime_t total;
> > -
> > -	do {
> > -		seq = read_seqcount_begin(&engine->stats.lock);
> > -		total = __intel_engine_get_busy_time(engine, now);
> > -	} while (read_seqcount_retry(&engine->stats.lock, seq));
> > -
> > -	return total;
> > +	return engine->busyness(engine, now);
> >   }
> >   
> >   struct intel_context *
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > index 5ae1207c363b..8e1b9c38a6fc 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > @@ -432,6 +432,12 @@ struct intel_engine_cs {
> >   	void		(*add_active_request)(struct i915_request *rq);
> >   	void		(*remove_active_request)(struct i915_request *rq);
> >   
> > +	/*
> > +	 * Get engine busyness and the time at which the busyness was sampled.
> > +	 */
> > +	ktime_t		(*busyness)(struct intel_engine_cs *engine,
> > +				    ktime_t *now);
> > +
> >   	struct intel_engine_execlists execlists;
> >   
> >   	/*
> > @@ -481,30 +487,66 @@ struct intel_engine_cs {
> >   	u32 (*get_cmd_length_mask)(u32 cmd_header);
> >   
> >   	struct {
> > -		/**
> > -		 * @active: Number of contexts currently scheduled in.
> > -		 */
> > -		unsigned int active;
> > -
> > -		/**
> > -		 * @lock: Lock protecting the below fields.
> > -		 */
> > -		seqcount_t lock;
> > -
> > -		/**
> > -		 * @total: Total time this engine was busy.
> > -		 *
> > -		 * Accumulated time not counting the most recent block in cases
> > -		 * where engine is currently busy (active > 0).
> > -		 */
> > -		ktime_t total;
> > -
> > -		/**
> > -		 * @start: Timestamp of the last idle to active transition.
> > -		 *
> > -		 * Idle is defined as active == 0, active is active > 0.
> > -		 */
> > -		ktime_t start;
> > +		union {
> > +			/* Fields used by the execlists backend. */
> > +			struct {
> > +				/**
> > +				 * @active: Number of contexts currently
> > +				 * scheduled in.
> > +				 */
> > +				unsigned int active;
> > +
> > +				/**
> > +				 * @lock: Lock protecting the below fields.
> > +				 */
> > +				seqcount_t lock;
> > +
> > +				/**
> > +				 * @total: Total time this engine was busy.
> > +				 *
> > +				 * Accumulated time not counting the most recent
> > +				 * block in cases where engine is currently busy
> > +				 * (active > 0).
> > +				 */
> > +				ktime_t total;
> > +
> > +				/**
> > +				 * @start: Timestamp of the last idle to active
> > +				 * transition.
> > +				 *
> > +				 * Idle is defined as active == 0, active is
> > +				 * active > 0.
> > +				 */
> > +				ktime_t start;
> > +			};
>
> Not anonymous? e.g.
>
> struct {
> 	...
> } execlists;
> struct {
> 	...
> } guc;
>
> IMO this is better as this is self documenting and if you touch an
> backend specific field in a non-backend specific file it pops out as
> incorrect.
>
> > +
> > +			/* Fields used by the GuC backend. */
> > +			struct {
> > +				/**
> > +				 * @running: Active state of the engine when
> > +				 * busyness was last sampled.
> > +				 */
> > +				bool running;
> > +
> > +				/**
> > +				 * @prev_total: Previous value of total runtime
> > +				 * clock cycles.
> > +				 */
> > +				u32 prev_total;
> > +
> > +				/**
> > +				 * @total_gt_clks: Total gt clock cycles this
> > +				 * engine was busy.
> > +				 */
> > +				u64 total_gt_clks;
> > +
> > +				/**
> > +				 * @start_gt_clk: GT clock time of last idle to
> > +				 * active transition.
> > +				 */
> > +				u64 start_gt_clk;
> > +			};
> > +		};
> >   
> >   		/**
> >   		 * @rps: Utilisation at last RPS sampling.
> > diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> > index 7147fe80919e..5c9b695e906c 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> > @@ -3292,6 +3292,36 @@ static void execlists_release(struct intel_engine_cs *engine)
> >   	lrc_fini_wa_ctx(engine);
> >   }
> >   
> > +static ktime_t __execlists_engine_busyness(struct intel_engine_cs *engine,
> > +					   ktime_t *now)
> > +{
> > +	ktime_t total = engine->stats.total;
> > +
> > +	/*
> > +	 * If the engine is executing something at the moment
> > +	 * add it to the total.
> > +	 */
> > +	*now = ktime_get();
> > +	if (READ_ONCE(engine->stats.active))
> > +		total = ktime_add(total, ktime_sub(*now, engine->stats.start));
> > +
> > +	return total;
> > +}
> > +
> > +static ktime_t execlists_engine_busyness(struct intel_engine_cs *engine,
> > +					 ktime_t *now)
> > +{
> > +	unsigned int seq;
> > +	ktime_t total;
> > +
> > +	do {
> > +		seq = read_seqcount_begin(&engine->stats.lock);
> > +		total = __execlists_engine_busyness(engine, now);
> > +	} while (read_seqcount_retry(&engine->stats.lock, seq));
> > +
> > +	return total;
> > +}
> > +
> >   static void
> >   logical_ring_default_vfuncs(struct intel_engine_cs *engine)
> >   {
> > @@ -3348,6 +3378,8 @@ logical_ring_default_vfuncs(struct intel_engine_cs *engine)
> >   		engine->emit_bb_start = gen8_emit_bb_start;
> >   	else
> >   		engine->emit_bb_start = gen8_emit_bb_start_noarb;
> > +
> > +	engine->busyness = execlists_engine_busyness;
> >   }
> >   
> >   static void logical_ring_default_irqs(struct intel_engine_cs *engine)
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> > index 524eaf678790..b4a8594bc46c 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> > @@ -86,6 +86,7 @@ static int __gt_unpark(struct intel_wakeref *wf)
> >   	intel_rc6_unpark(&gt->rc6);
> >   	intel_rps_unpark(&gt->rps);
> >   	i915_pmu_gt_unparked(i915);
> > +	intel_guc_busyness_unpark(gt);
>
> I personally don't mind this but in the spirit of correct layering, this
> likely should be generic wrapper inline func which calls a vfunc if
> present (e.g. set the vfunc for backend, don't set for execlists).
>
> >   
> >   	intel_gt_unpark_requests(gt);
> >   	runtime_begin(gt);
> > @@ -104,6 +105,7 @@ static int __gt_park(struct intel_wakeref *wf)
> >   	runtime_end(gt);
> >   	intel_gt_park_requests(gt);
> >   
> > +	intel_guc_busyness_park(gt);
>
> Same here.
>
> >   	i915_vma_parked(gt);
> >   	i915_pmu_gt_parked(i915);
> >   	intel_rps_park(&gt->rps);
> > diff --git a/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h b/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h
> > index 8ff582222aff..ff1311d4beff 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h
> > @@ -143,6 +143,7 @@ enum intel_guc_action {
> >   	INTEL_GUC_ACTION_DEREGISTER_COMMAND_TRANSPORT_BUFFER = 0x4506,
> >   	INTEL_GUC_ACTION_DEREGISTER_CONTEXT_DONE = 0x4600,
> >   	INTEL_GUC_ACTION_RESET_CLIENT = 0x5507,
> > +	INTEL_GUC_ACTION_SET_ENG_UTIL_BUFF = 0x550A,
> >   	INTEL_GUC_ACTION_LIMIT
> >   };
> >   
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > index 5dd174babf7a..22c30dbdf63a 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > @@ -104,6 +104,8 @@ struct intel_guc {
> >   	u32 ads_regset_size;
> >   	/** @ads_golden_ctxt_size: size of the golden contexts in the ADS */
> >   	u32 ads_golden_ctxt_size;
> > +	/** @ads_engine_usage_size: size of engine usage in the ADS */
> > +	u32 ads_engine_usage_size;
> >   
> >   	/** @lrc_desc_pool: object allocated to hold the GuC LRC descriptor pool */
> >   	struct i915_vma *lrc_desc_pool;
> > @@ -138,6 +140,30 @@ struct intel_guc {
> >   
> >   	/** @send_mutex: used to serialize the intel_guc_send actions */
> >   	struct mutex send_mutex;
> > +
> > +	struct {
> > +		/**
> > +		 * @lock: Lock protecting the below fields and the engine stats.
> > +		 */
> > +		spinlock_t lock;
> > +
>
> Again I really don't mind but I'm told not to add more spin locks than
> needed. This really should be protected by a generic GuC submission spin
> lock. e.g. Build on this patch and protect all of this by the
> submission_state.lock.

I see no good reason to use the submission lock here. The two are 
completely different paths, with completely different entry points and 
we don't want to introduce contention where it is trivially avoidable 
for no real cost. In other words I think this lock is well defined and 
localised both in code and in execution flows.

Regards,

Tvrtko

> https://patchwork.freedesktop.org/patch/457310/?series=92789&rev=5
>
> Whomevers series gets merged first can include the above patch.
>
> Rest the series looks fine cosmetically to me.
>
> Matt
>
> > +		/**
> > +		 * @gt_stamp: 64 bit extended value of the GT timestamp.
> > +		 */
> > +		u64 gt_stamp;
> > +
> > +		/**
> > +		 * @ping_delay: Period for polling the GT timestamp for
> > +		 * overflow.
> > +		 */
> > +		unsigned long ping_delay;
> > +
> > +		/**
> > +		 * @work: Periodic work to adjust GT timestamp, engine and
> > +		 * context usage for overflows.
> > +		 */
> > +		struct delayed_work work;
> > +	} timestamp;
> >   };
> >   
> >   static inline struct intel_guc *log_to_guc(struct intel_guc_log *log)
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c
> > index 2c6ea64af7ec..ca9ab53999d5 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c
> > @@ -26,6 +26,8 @@
> >    *      | guc_policies                          |
> >    *      +---------------------------------------+
> >    *      | guc_gt_system_info                    |
> > + *      +---------------------------------------+
> > + *      | guc_engine_usage                      |
> >    *      +---------------------------------------+ <== static
> >    *      | guc_mmio_reg[countA] (engine 0.0)     |
> >    *      | guc_mmio_reg[countB] (engine 0.1)     |
> > @@ -47,6 +49,7 @@ struct __guc_ads_blob {
> >   	struct guc_ads ads;
> >   	struct guc_policies policies;
> >   	struct guc_gt_system_info system_info;
> > +	struct guc_engine_usage engine_usage;
> >   	/* From here on, location is dynamic! Refer to above diagram. */
> >   	struct guc_mmio_reg regset[0];
> >   } __packed;
> > @@ -628,3 +631,21 @@ void intel_guc_ads_reset(struct intel_guc *guc)
> >   
> >   	guc_ads_private_data_reset(guc);
> >   }
> > +
> > +u32 intel_guc_engine_usage_offset(struct intel_guc *guc)
> > +{
> > +	struct __guc_ads_blob *blob = guc->ads_blob;
> > +	u32 base = intel_guc_ggtt_offset(guc, guc->ads_vma);
> > +	u32 offset = base + ptr_offset(blob, engine_usage);
> > +
> > +	return offset;
> > +}
> > +
> > +struct guc_engine_usage_record *intel_guc_engine_usage(struct intel_engine_cs *engine)
> > +{
> > +	struct intel_guc *guc = &engine->gt->uc.guc;
> > +	struct __guc_ads_blob *blob = guc->ads_blob;
> > +	u8 guc_class = engine_class_to_guc_class(engine->class);
> > +
> > +	return &blob->engine_usage.engines[guc_class][engine->instance];
> > +}
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.h
> > index 3d85051d57e4..e74c110facff 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ads.h
> > @@ -6,8 +6,11 @@
> >   #ifndef _INTEL_GUC_ADS_H_
> >   #define _INTEL_GUC_ADS_H_
> >   
> > +#include <linux/types.h>
> > +
> >   struct intel_guc;
> >   struct drm_printer;
> > +struct intel_engine_cs;
> >   
> >   int intel_guc_ads_create(struct intel_guc *guc);
> >   void intel_guc_ads_destroy(struct intel_guc *guc);
> > @@ -15,5 +18,7 @@ void intel_guc_ads_init_late(struct intel_guc *guc);
> >   void intel_guc_ads_reset(struct intel_guc *guc);
> >   void intel_guc_ads_print_policy_info(struct intel_guc *guc,
> >   				     struct drm_printer *p);
> > +struct guc_engine_usage_record *intel_guc_engine_usage(struct intel_engine_cs *engine);
> > +u32 intel_guc_engine_usage_offset(struct intel_guc *guc);
> >   
> >   #endif
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
> > index fa4be13c8854..7c9c081670fc 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
> > @@ -294,6 +294,19 @@ struct guc_ads {
> >   	u32 reserved[15];
> >   } __packed;
> >   
> > +/* Engine usage stats */
> > +struct guc_engine_usage_record {
> > +	u32 current_context_index;
> > +	u32 last_switch_in_stamp;
> > +	u32 reserved0;
> > +	u32 total_runtime;
> > +	u32 reserved1[4];
> > +} __packed;
> > +
> > +struct guc_engine_usage {
> > +	struct guc_engine_usage_record engines[GUC_MAX_ENGINE_CLASSES][GUC_MAX_INSTANCES_PER_CLASS];
> > +} __packed;
> > +
> >   /* GuC logging structures */
> >   
> >   enum guc_log_buffer_type {
> > 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..3f7d0f2ac9da 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -12,6 +12,7 @@
> >   #include "gt/intel_engine_pm.h"
> >   #include "gt/intel_engine_heartbeat.h"
> >   #include "gt/intel_gt.h"
> > +#include "gt/intel_gt_clock_utils.h"
> >   #include "gt/intel_gt_irq.h"
> >   #include "gt/intel_gt_pm.h"
> >   #include "gt/intel_gt_requests.h"
> > @@ -20,6 +21,7 @@
> >   #include "gt/intel_mocs.h"
> >   #include "gt/intel_ring.h"
> >   
> > +#include "intel_guc_ads.h"
> >   #include "intel_guc_submission.h"
> >   
> >   #include "i915_drv.h"
> > @@ -762,12 +764,25 @@ submission_disabled(struct intel_guc *guc)
> >   static void disable_submission(struct intel_guc *guc)
> >   {
> >   	struct i915_sched_engine * const sched_engine = guc->sched_engine;
> > +	struct intel_gt *gt = guc_to_gt(guc);
> > +	struct intel_engine_cs *engine;
> > +	enum intel_engine_id id;
> > +	unsigned long flags;
> >   
> >   	if (__tasklet_is_enabled(&sched_engine->tasklet)) {
> >   		GEM_BUG_ON(!guc->ct.enabled);
> >   		__tasklet_disable_sync_once(&sched_engine->tasklet);
> >   		sched_engine->tasklet.callback = NULL;
> >   	}
> > +
> > +	cancel_delayed_work(&guc->timestamp.work);
> > +
> > +	spin_lock_irqsave(&guc->timestamp.lock, flags);
> > +
> > +	for_each_engine(engine, gt, id)
> > +		engine->stats.prev_total = 0;
> > +
> > +	spin_unlock_irqrestore(&guc->timestamp.lock, flags);
> >   }
> >   
> >   static void enable_submission(struct intel_guc *guc)
> > @@ -1126,12 +1141,217 @@ void intel_guc_submission_reset_finish(struct intel_guc *guc)
> >   	intel_gt_unpark_heartbeats(guc_to_gt(guc));
> >   }
> >   
> > +/*
> > + * GuC stores busyness stats for each engine at context in/out boundaries. A
> > + * context 'in' logs execution start time, 'out' adds in -> out delta to total.
> > + * i915/kmd accesses 'start', 'total' and 'context id' from memory shared with
> > + * GuC.
> > + *
> > + * __i915_pmu_event_read samples engine busyness. When sampling, if context id
> > + * is valid (!= ~0) and start is non-zero, the engine is considered to be
> > + * active. For an active engine total busyness = total + (now - start), where
> > + * 'now' is the time at which the busyness is sampled. For inactive engine,
> > + * total busyness = total.
> > + *
> > + * All times are captured from GUCPMTIMESTAMP reg and are in gt clock domain.
> > + *
> > + * The start and total values provided by GuC are 32 bits and wrap around in a
> > + * few minutes. Since perf pmu provides busyness as 64 bit monotonically
> > + * increasing ns values, there is a need for this implementation to account for
> > + * overflows and extend the GuC provided values to 64 bits before returning
> > + * busyness to the user. In order to do that, a worker runs periodically at
> > + * frequency = 1/8th the time it takes for the timestamp to wrap (i.e. once in
> > + * 27 seconds for a gt clock frequency of 19.2 MHz).
> > + */
> > +
> > +#define WRAP_TIME_CLKS U32_MAX
> > +#define POLL_TIME_CLKS (WRAP_TIME_CLKS >> 3)
> > +
> > +static void
> > +__extend_last_switch(struct intel_guc *guc, u64 *prev_start, u32 new_start)
> > +{
> > +	u32 gt_stamp_hi = upper_32_bits(guc->timestamp.gt_stamp);
> > +	u32 gt_stamp_last = lower_32_bits(guc->timestamp.gt_stamp);
> > +
> > +	if (new_start == lower_32_bits(*prev_start))
> > +		return;
> > +
> > +	if (new_start < gt_stamp_last &&
> > +	    (new_start - gt_stamp_last) <= POLL_TIME_CLKS)
> > +		gt_stamp_hi++;
> > +
> > +	if (new_start > gt_stamp_last &&
> > +	    (gt_stamp_last - new_start) <= POLL_TIME_CLKS && gt_stamp_hi)
> > +		gt_stamp_hi--;
> > +
> > +	*prev_start = ((u64)gt_stamp_hi << 32) | new_start;
> > +}
> > +
> > +static void guc_update_engine_gt_clks(struct intel_engine_cs *engine)
> > +{
> > +	struct guc_engine_usage_record *rec = intel_guc_engine_usage(engine);
> > +	struct intel_guc *guc = &engine->gt->uc.guc;
> > +	u32 last_switch = rec->last_switch_in_stamp;
> > +	u32 ctx_id = rec->current_context_index;
> > +	u32 total = rec->total_runtime;
> > +
> > +	lockdep_assert_held(&guc->timestamp.lock);
> > +
> > +	engine->stats.running = ctx_id != ~0U && last_switch;
> > +	if (engine->stats.running)
> > +		__extend_last_switch(guc, &engine->stats.start_gt_clk,
> > +				     last_switch);
> > +
> > +	/*
> > +	 * Instead of adjusting the total for overflow, just add the
> > +	 * difference from previous sample to the stats.total_gt_clks
> > +	 */
> > +	if (total && total != ~0U) {
> > +		engine->stats.total_gt_clks += (u32)(total -
> > +						     engine->stats.prev_total);
> > +		engine->stats.prev_total = total;
> > +	}
> > +}
> > +
> > +static void guc_update_pm_timestamp(struct intel_guc *guc)
> > +{
> > +	struct intel_gt *gt = guc_to_gt(guc);
> > +	u32 gt_stamp_now, gt_stamp_hi;
> > +
> > +	lockdep_assert_held(&guc->timestamp.lock);
> > +
> > +	gt_stamp_hi = upper_32_bits(guc->timestamp.gt_stamp);
> > +	gt_stamp_now = intel_uncore_read(gt->uncore, GUCPMTIMESTAMP);
> > +
> > +	if (gt_stamp_now < lower_32_bits(guc->timestamp.gt_stamp))
> > +		gt_stamp_hi++;
> > +
> > +	guc->timestamp.gt_stamp = ((u64) gt_stamp_hi << 32) | gt_stamp_now;
> > +}
> > +
> > +/*
> > + * Unlike the execlist mode of submission total and active times are in terms of
> > + * gt clocks. The *now parameter is retained to return the cpu time at which the
> > + * busyness was sampled.
> > + */
> > +static ktime_t guc_engine_busyness(struct intel_engine_cs *engine, ktime_t *now)
> > +{
> > +	struct intel_gt *gt = engine->gt;
> > +	struct intel_guc *guc = &gt->uc.guc;
> > +	unsigned long flags;
> > +	u64 total;
> > +
> > +	spin_lock_irqsave(&guc->timestamp.lock, flags);
> > +
> > +	*now = ktime_get();
> > +
> > +	/*
> > +	 * The active busyness depends on start_gt_clk and gt_stamp.
> > +	 * gt_stamp is updated by i915 only when gt is awake and the
> > +	 * start_gt_clk is derived from GuC state. To get a consistent
> > +	 * view of activity, we query the GuC state only if gt is awake.
> > +	 */
> > +	if (intel_gt_pm_get_if_awake(gt)) {
> > +		guc_update_engine_gt_clks(engine);
> > +		guc_update_pm_timestamp(guc);
> > +		intel_gt_pm_put_async(gt);
> > +	}
> > +
> > +	total = intel_gt_clock_interval_to_ns(gt, engine->stats.total_gt_clks);
> > +	if (engine->stats.running) {
> > +		u64 clk = guc->timestamp.gt_stamp - engine->stats.start_gt_clk;
> > +
> > +		total += intel_gt_clock_interval_to_ns(gt, clk);
> > +	}
> > +
> > +	spin_unlock_irqrestore(&guc->timestamp.lock, flags);
> > +
> > +	return ns_to_ktime(total);
> > +}
> > +
> > +static void __update_guc_busyness_stats(struct intel_guc *guc)
> > +{
> > +	struct intel_gt *gt = guc_to_gt(guc);
> > +	struct intel_engine_cs *engine;
> > +	enum intel_engine_id id;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&guc->timestamp.lock, flags);
> > +
> > +	if (intel_gt_pm_get_if_awake(gt)) {
> > +		guc_update_pm_timestamp(guc);
> > +
> > +		for_each_engine(engine, gt, id)
> > +			guc_update_engine_gt_clks(engine);
> > +
> > +		intel_gt_pm_put_async(gt);
> > +	}
> > +
> > +	spin_unlock_irqrestore(&guc->timestamp.lock, flags);
> > +}
> > +
> > +static void guc_timestamp_ping(struct work_struct *wrk)
> > +{
> > +	struct intel_guc *guc = container_of(wrk, typeof(*guc),
> > +					     timestamp.work.work);
> > +
> > +	__update_guc_busyness_stats(guc);
> > +	mod_delayed_work(system_highpri_wq, &guc->timestamp.work,
> > +			 guc->timestamp.ping_delay);
> > +}
> > +
> > +static int guc_action_enable_usage_stats(struct intel_guc *guc)
> > +{
> > +	u32 offset = intel_guc_engine_usage_offset(guc);
> > +	u32 action[] = {
> > +		INTEL_GUC_ACTION_SET_ENG_UTIL_BUFF,
> > +		offset,
> > +		0,
> > +	};
> > +
> > +	return intel_guc_send(guc, action, ARRAY_SIZE(action));
> > +}
> > +
> > +static void guc_init_engine_stats(struct intel_guc *guc)
> > +{
> > +	struct intel_gt *gt = guc_to_gt(guc);
> > +	intel_wakeref_t wakeref;
> > +
> > +	mod_delayed_work(system_highpri_wq, &guc->timestamp.work,
> > +			 guc->timestamp.ping_delay);
> > +
> > +	with_intel_runtime_pm(&gt->i915->runtime_pm, wakeref) {
> > +		int ret = guc_action_enable_usage_stats(guc);
> > +
> > +		if (ret)
> > +			drm_err(&gt->i915->drm,
> > +				"Failed to enable usage stats: %d!\n", ret);
> > +	}
> > +}
> > +
> > +void intel_guc_busyness_park(struct intel_gt *gt)
> > +{
> > +	struct intel_guc *guc = &gt->uc.guc;
> > +
> > +	cancel_delayed_work(&guc->timestamp.work);
> > +	__update_guc_busyness_stats(guc);
> > +}
> > +
> > +void intel_guc_busyness_unpark(struct intel_gt *gt)
> > +{
> > +	struct intel_guc *guc = &gt->uc.guc;
> > +
> > +	mod_delayed_work(system_highpri_wq, &guc->timestamp.work,
> > +			 guc->timestamp.ping_delay);
> > +}
> > +
> >   /*
> >    * Set up the memory resources to be shared with the GuC (via the GGTT)
> >    * at firmware loading time.
> >    */
> >   int intel_guc_submission_init(struct intel_guc *guc)
> >   {
> > +	struct intel_gt *gt = guc_to_gt(guc);
> >   	int ret;
> >   
> >   	if (guc->lrc_desc_pool)
> > @@ -1152,6 +1372,10 @@ int intel_guc_submission_init(struct intel_guc *guc)
> >   	INIT_LIST_HEAD(&guc->guc_id_list);
> >   	ida_init(&guc->guc_ids);
> >   
> > +	spin_lock_init(&guc->timestamp.lock);
> > +	INIT_DELAYED_WORK(&guc->timestamp.work, guc_timestamp_ping);
> > +	guc->timestamp.ping_delay = (POLL_TIME_CLKS / gt->clock_frequency + 1) * HZ;
> > +
> >   	return 0;
> >   }
> >   
> > @@ -2606,7 +2830,9 @@ static void guc_default_vfuncs(struct intel_engine_cs *engine)
> >   		engine->emit_flush = gen12_emit_flush_xcs;
> >   	}
> >   	engine->set_default_submission = guc_set_default_submission;
> > +	engine->busyness = guc_engine_busyness;
> >   
> > +	engine->flags |= I915_ENGINE_SUPPORTS_STATS;
> >   	engine->flags |= I915_ENGINE_HAS_PREEMPTION;
> >   	engine->flags |= I915_ENGINE_HAS_TIMESLICES;
> >   
> > @@ -2705,6 +2931,7 @@ int intel_guc_submission_setup(struct intel_engine_cs *engine)
> >   void intel_guc_submission_enable(struct intel_guc *guc)
> >   {
> >   	guc_init_lrc_mapping(guc);
> > +	guc_init_engine_stats(guc);
> >   }
> >   
> >   void intel_guc_submission_disable(struct intel_guc *guc)
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h
> > index c7ef44fa0c36..5a95a9f0a8e3 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h
> > @@ -28,6 +28,8 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
> >   void intel_guc_dump_active_requests(struct intel_engine_cs *engine,
> >   				    struct i915_request *hung_rq,
> >   				    struct drm_printer *m);
> > +void intel_guc_busyness_park(struct intel_gt *gt);
> > +void intel_guc_busyness_unpark(struct intel_gt *gt);
> >   
> >   bool intel_guc_virtual_engine_has_heartbeat(const struct intel_engine_cs *ve);
> >   
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index a897f4abea0c..9aee08425382 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -2664,6 +2664,8 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
> >   #define   RING_WAIT		(1 << 11) /* gen3+, PRBx_CTL */
> >   #define   RING_WAIT_SEMAPHORE	(1 << 10) /* gen6+ */
> >   
> > +#define GUCPMTIMESTAMP          _MMIO(0xC3E8)
> > +
> >   /* There are 16 64-bit CS General Purpose Registers per-engine on Gen8+ */
> >   #define GEN8_RING_CS_GPR(base, n)	_MMIO((base) + 0x600 + (n) * 8)
> >   #define GEN8_RING_CS_GPR_UDW(base, n)	_MMIO((base) + 0x600 + (n) * 8 + 4)
> > --
> > 2.20.1