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Subject: Re: [Intel-gfx] [RFC 7/8] drm/i915: Inherit process nice for context
 scheduling priority
To:     Matthew Brost <matthew.brost@intel.com>
Cc:     Intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org,
        Tvrtko Ursulin <tvrtko.ursulin@intel.com>
References: <20211004143650.699120-1-tvrtko.ursulin@linux.intel.com>
 <20211004143650.699120-8-tvrtko.ursulin@linux.intel.com>
 <20211006172450.GA8103@jons-linux-dev-box>
From:   Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Organization: Intel Corporation UK Plc
Message-ID: <11356daf-ddde-6822-d578-e57f875ec22d@linux.intel.com>
Date:   Wed, 6 Oct 2021 19:42:37 +0100
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On 06/10/2021 18:24, Matthew Brost wrote:
> On Mon, Oct 04, 2021 at 03:36:49PM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> Introduce the concept of context nice value which matches the process
>> nice.
>>
>> We do this by extending the struct i915_sched_attr and add a helper
>> (i915_sched_attr_priority) to be used to convert to effective priority
>> when used by backend code and for priority sorting.
>>
>> Context nice is then inherited from the process which creates the GEM
>> context and utilised secondary to context priority, only when the latter
>> has been left at the default setting, in order to avoid disturbing any
>> application made choices of low and high (batch processing and maybe
>> latency sensitive compositing). In those cases nice value adjusts the
>> effective priority in the narrow band of -19 to +20 around
>> I915_CONTEXT_DEFAULT_PRIORITY.
>>
>> This means that in theory userspace using the context priority uapi
>> directly has a wider range of possible adjustments (thought to be
>> beneficial), but in practice that only applies to execlists platforms.
>> With GuC there are only three priority buckets (less than zero is low
>> priority, zero is normal and greater than zero is high) which therefore
>> interact as expected with the nice adjustment. It makes the question of
>> should the nice be a sub-range of GEM priorities, or stretched across the
>> whole, a moot one.
>>
> 
> Opps, sorry for the double reply to this patch - for some reason I
> thinking the below comment would be on the next patch.
> 
> The GuC + DRM scheduler actually has 4 priorities with the highest
> reserved for the KMD, so 3 user levels which is what I think you mean.
> So how would this work with only 3 levels?
 >
 > The nice value can move a normal priority value to either low or high,
 > right?

Yes. I was thinking about three user visible levels. The kernel one is 
reserved for internal stuff so I did not mention it.

Default, nice 0 = normal priority.
Positive nice = low priority.
Negative nice = high priority.

Same as mapping of -1024 to 1023 range works onto those three AFAIU. So 
I think it works.

> Normal to low seems fine but would moving to high be an issue?
> 
> I thought a high level was reserved for elevated user processes (e.g. a
> root user or a compositor)?

Yes, and lowering the nice (negative nice) also needs CAP_SYS_NICE which 
is not available to user processes by default. So that matches i915 
rules with going above default/normal.

> Would it be ok for a non-elevated user process to be the same priority
> as an elevated process?

Not sure exactly what you have in mind but in principle yes. Same as it 
is okay for all current greater than zero priorities to map to a single 
priority in case of GuC.

Regards,

Tvrtko

> 
> Matt
> 
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> ---
>>   drivers/gpu/drm/i915/gem/i915_gem_context.c        |  1 +
>>   .../gpu/drm/i915/gt/intel_execlists_submission.c   |  4 ++--
>>   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c  |  2 +-
>>   drivers/gpu/drm/i915/i915_request.c                |  2 +-
>>   drivers/gpu/drm/i915/i915_request.h                |  5 +++++
>>   drivers/gpu/drm/i915/i915_scheduler.c              | 12 ++++++++----
>>   drivers/gpu/drm/i915/i915_scheduler.h              | 14 ++++++++++++++
>>   drivers/gpu/drm/i915/i915_scheduler_types.h        |  8 ++++++++
>>   8 files changed, 40 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> index 8d4d687ab1d0..fed0733cb652 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> @@ -257,6 +257,7 @@ proto_context_create(struct drm_i915_private *i915, unsigned int flags)
>>   	if (i915->params.enable_hangcheck)
>>   		pc->user_flags |= BIT(UCONTEXT_PERSISTENCE);
>>   	pc->sched.priority = I915_PRIORITY_NORMAL;
>> +	pc->sched.nice = task_nice(current);
>>   
>>   	if (flags & I915_CONTEXT_CREATE_FLAGS_SINGLE_TIMELINE) {
>>   		if (!HAS_EXECLISTS(i915)) {
>> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
>> index e91d803a6453..1a02c65823a7 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
>> @@ -250,7 +250,7 @@ static struct i915_priolist *to_priolist(struct rb_node *rb)
>>   
>>   static int rq_prio(const struct i915_request *rq)
>>   {
>> -	return READ_ONCE(rq->sched.attr.priority);
>> +	return i915_request_priority(rq);
>>   }
>>   
>>   static int effective_prio(const struct i915_request *rq)
>> @@ -3221,8 +3221,8 @@ static void kick_execlists(const struct i915_request *rq,
>>   {
>>   	struct intel_engine_cs *engine = rq->engine;
>>   	struct i915_sched_engine *sched_engine = engine->sched_engine;
>> +	const int prio = i915_sched_attr_priority(attr);
>>   	const struct i915_request *inflight;
>> -	const int prio = attr->priority;
>>   
>>   	/*
>>   	 * We only need to kick the tasklet once for the high priority
>> 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 b5883a4365ca..f258607685a2 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>> @@ -2417,7 +2417,7 @@ static void guc_bump_inflight_request_prio(struct i915_request *rq,
>>   					   const struct i915_sched_attr *attr)
>>   {
>>   	struct intel_context *ce = rq->context;
>> -	const int prio = attr->priority;
>> +	const int prio = i915_sched_attr_priority(attr);
>>   	u8 new_guc_prio = map_i915_prio_to_guc_prio(prio);
>>   
>>   	/* Short circuit function */
>> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
>> index 79da5eca60af..a8c6f3a64895 100644
>> --- a/drivers/gpu/drm/i915/i915_request.c
>> +++ b/drivers/gpu/drm/i915/i915_request.c
>> @@ -1930,7 +1930,7 @@ static int print_sched_attr(const struct i915_sched_attr *attr,
>>   		return x;
>>   
>>   	x += snprintf(buf + x, len - x,
>> -		      " prio=%d", attr->priority);
>> +		      " prio=%d nice=%d", attr->priority, attr->nice);
>>   
>>   	return x;
>>   }
>> diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
>> index 7bd9ed20623e..c2c4c344837e 100644
>> --- a/drivers/gpu/drm/i915/i915_request.h
>> +++ b/drivers/gpu/drm/i915/i915_request.h
>> @@ -399,6 +399,11 @@ long i915_request_wait(struct i915_request *rq,
>>   #define I915_WAIT_PRIORITY	BIT(1) /* small priority bump for the request */
>>   #define I915_WAIT_ALL		BIT(2) /* used by i915_gem_object_wait() */
>>   
>> +static inline int i915_request_priority(const struct i915_request *rq)
>> +{
>> +	return i915_sched_attr_priority(&rq->sched.attr);
>> +}
>> +
>>   void i915_request_show(struct drm_printer *m,
>>   		       const struct i915_request *rq,
>>   		       const char *prefix,
>> diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
>> index 534bab99fcdc..e75793e36454 100644
>> --- a/drivers/gpu/drm/i915/i915_scheduler.c
>> +++ b/drivers/gpu/drm/i915/i915_scheduler.c
>> @@ -155,7 +155,9 @@ lock_sched_engine(struct i915_sched_node *node,
>>   static void __i915_schedule(struct i915_sched_node *node,
>>   			    const struct i915_sched_attr *attr)
>>   {
>> -	const int prio = max(attr->priority, node->attr.priority);
>> +	const int prio =
>> +		max(i915_sched_attr_priority(attr),
>> +		    i915_sched_attr_priority(&node->attr));
>>   	struct i915_sched_engine *sched_engine;
>>   	struct i915_dependency *dep, *p;
>>   	struct i915_dependency stack;
>> @@ -209,7 +211,7 @@ static void __i915_schedule(struct i915_sched_node *node,
>>   			if (node_signaled(p->signaler))
>>   				continue;
>>   
>> -			if (prio > READ_ONCE(p->signaler->attr.priority))
>> +			if (prio > i915_sched_attr_priority(&p->signaler->attr))
>>   				list_move_tail(&p->dfs_link, &dfs);
>>   		}
>>   	}
>> @@ -247,7 +249,8 @@ static void __i915_schedule(struct i915_sched_node *node,
>>   		lockdep_assert_held(&sched_engine->lock);
>>   
>>   		/* Recheck after acquiring the engine->timeline.lock */
>> -		if (prio <= node->attr.priority || node_signaled(node))
>> +		if (prio <= i915_sched_attr_priority(&node->attr) ||
>> +		    node_signaled(node))
>>   			continue;
>>   
>>   		GEM_BUG_ON(node_to_request(node)->engine->sched_engine !=
>> @@ -257,7 +260,7 @@ static void __i915_schedule(struct i915_sched_node *node,
>>   		if (sched_engine->bump_inflight_request_prio)
>>   			sched_engine->bump_inflight_request_prio(from, attr);
>>   
>> -		WRITE_ONCE(node->attr.priority, prio);
>> +		WRITE_ONCE(node->attr, *attr);
>>   
>>   		/*
>>   		 * Once the request is ready, it will be placed into the
>> @@ -305,6 +308,7 @@ void i915_sched_node_init(struct i915_sched_node *node)
>>   void i915_sched_node_reinit(struct i915_sched_node *node)
>>   {
>>   	node->attr.priority = I915_PRIORITY_INVALID;
>> +	node->attr.nice = 0;
>>   	node->semaphores = 0;
>>   	node->flags = 0;
>>   
>> diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h
>> index 0b9b86af6c7f..75ccc9f55d14 100644
>> --- a/drivers/gpu/drm/i915/i915_scheduler.h
>> +++ b/drivers/gpu/drm/i915/i915_scheduler.h
>> @@ -38,6 +38,20 @@ void i915_sched_node_fini(struct i915_sched_node *node);
>>   void i915_schedule(struct i915_request *request,
>>   		   const struct i915_sched_attr *attr);
>>   
>> +static inline int i915_sched_attr_priority(const struct i915_sched_attr *attr)
>> +{
>> +	int prio = attr->priority;
>> +
>> +	/*
>> +	 * Only allow I915_CONTEXT_DEFAULT_PRIORITY to be affected by the
>> +	 * nice setting.
>> +	 */
>> +	if (!prio)
>> +		prio = -attr->nice;
>> +
>> +	return prio;
>> +}
>> +
>>   struct list_head *
>>   i915_sched_lookup_priolist(struct i915_sched_engine *sched_engine, int prio);
>>   
>> diff --git a/drivers/gpu/drm/i915/i915_scheduler_types.h b/drivers/gpu/drm/i915/i915_scheduler_types.h
>> index 24b9ac1c2ce2..159237aa7609 100644
>> --- a/drivers/gpu/drm/i915/i915_scheduler_types.h
>> +++ b/drivers/gpu/drm/i915/i915_scheduler_types.h
>> @@ -29,6 +29,14 @@ struct i915_sched_attr {
>>   	 * The &drm_i915_private.kernel_context is assigned the lowest priority.
>>   	 */
>>   	int priority;
>> +
>> +	/**
>> +	 * @nice: context nice level
>> +	 *
>> +	 * Nice level follows the CPU scheduler nice value as set for the
>> +	 * process owning the GPU context.
>> +	 */
>> +	int nice;
>>   };
>>   
>>   /*
>> -- 
>> 2.30.2
>>