Re: [Intel-gfx] [RFC 7/8] drm/i915: Inherit process nice for context scheduling priority

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