Re: [Intel-gfx] [PATCH 2/3] drm/i915/gt: create workqueue dedicated to wake references

["Coelho, Luciano" <luciano.coelho@intel.com>]

On Fri, 2023-05-12 at 10:04 +0100, Tvrtko Ursulin wrote:
> On 11/05/2023 09:20, Luca Coelho wrote:
> > Add a work queue in the intel_wakeref structure to be used exclusively
> > by the wake reference mechanism.  This is needed in order to avoid
> > using the system workqueue and relying on flush_scheduled_work().
> > 
> > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_engine_cs.c |  7 ++++++-
> >   drivers/gpu/drm/i915/gt/intel_engine_pm.c | 15 ++++++++++++--
> >   drivers/gpu/drm/i915/gt/intel_engine_pm.h |  3 ++-
> >   drivers/gpu/drm/i915/gt/mock_engine.c     |  8 +++++++-
> >   drivers/gpu/drm/i915/intel_wakeref.c      | 21 ++++++++++++++-----
> >   drivers/gpu/drm/i915/intel_wakeref.h      | 25 +++++++++++++++--------
> >   6 files changed, 60 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > index 0aff5bb13c53..6505bfa70cd0 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > @@ -1290,7 +1290,11 @@ static int engine_setup_common(struct intel_engine_cs *engine)
> >   		goto err_cmd_parser;
> >   
> >   	intel_engine_init_execlists(engine);
> > -	intel_engine_init__pm(engine);
> > +
> > +	err = intel_engine_init__pm(engine);
> > +	if (err)
> > +		goto err_cmd_parser;
> > +
> >   	intel_engine_init_retire(engine);
> >   
> >   	/* Use the whole device by default */
> > @@ -1525,6 +1529,7 @@ void intel_engine_cleanup_common(struct intel_engine_cs *engine)
> >   {
> >   	GEM_BUG_ON(!list_empty(&engine->sched_engine->requests));
> >   
> > +	intel_engine_destroy__pm(engine);
> >   	i915_sched_engine_put(engine->sched_engine);
> >   	intel_breadcrumbs_put(engine->breadcrumbs);
> >   
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> > index ee531a5c142c..859b62cf660f 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> > @@ -294,14 +294,25 @@ static const struct intel_wakeref_ops wf_ops = {
> >   	.put = __engine_park,
> >   };
> >   
> > -void intel_engine_init__pm(struct intel_engine_cs *engine)
> > +int intel_engine_init__pm(struct intel_engine_cs *engine)
> >   {
> >   	struct intel_runtime_pm *rpm = engine->uncore->rpm;
> > +	int err;
> > +
> > +	err = intel_wakeref_init(&engine->wakeref, rpm, &wf_ops);
> > +	if (err)
> > +		return err;
> >   
> > -	intel_wakeref_init(&engine->wakeref, rpm, &wf_ops);
> >   	intel_engine_init_heartbeat(engine);
> >   
> >   	intel_gsc_idle_msg_enable(engine);
> > +
> > +	return 0;
> > +}
> > +
> > +void intel_engine_destroy__pm(struct intel_engine_cs *engine)
> > +{
> > +	intel_wakeref_destroy(&engine->wakeref);
> >   }
> >   
> >   /**
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.h b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
> > index d68675925b79..e8568f7d10c6 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
> > @@ -104,7 +104,8 @@ intel_engine_create_kernel_request(struct intel_engine_cs *engine)
> >   	return rq;
> >   }
> >   
> > -void intel_engine_init__pm(struct intel_engine_cs *engine);
> > +int intel_engine_init__pm(struct intel_engine_cs *engine);
> > +void intel_engine_destroy__pm(struct intel_engine_cs *engine);
> >   
> >   void intel_engine_reset_pinned_contexts(struct intel_engine_cs *engine);
> >   
> > diff --git a/drivers/gpu/drm/i915/gt/mock_engine.c b/drivers/gpu/drm/i915/gt/mock_engine.c
> > index c0637bf799a3..0a3c702c21e2 100644
> > --- a/drivers/gpu/drm/i915/gt/mock_engine.c
> > +++ b/drivers/gpu/drm/i915/gt/mock_engine.c
> > @@ -336,6 +336,7 @@ static void mock_engine_release(struct intel_engine_cs *engine)
> >   	intel_context_put(engine->kernel_context);
> >   
> >   	intel_engine_fini_retire(engine);
> > +	intel_engine_destroy__pm(engine);
> >   }
> >   
> >   struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
> > @@ -393,6 +394,7 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
> >   int mock_engine_init(struct intel_engine_cs *engine)
> >   {
> >   	struct intel_context *ce;
> > +	int err;
> >   
> >   	INIT_LIST_HEAD(&engine->pinned_contexts_list);
> >   
> > @@ -402,7 +404,11 @@ int mock_engine_init(struct intel_engine_cs *engine)
> >   	engine->sched_engine->private_data = engine;
> >   
> >   	intel_engine_init_execlists(engine);
> > -	intel_engine_init__pm(engine);
> > +
> > +	err = intel_engine_init__pm(engine);
> > +	if (err)
> > +		return err;
> > +
> >   	intel_engine_init_retire(engine);
> >   
> >   	engine->breadcrumbs = intel_breadcrumbs_create(NULL);
> > diff --git a/drivers/gpu/drm/i915/intel_wakeref.c b/drivers/gpu/drm/i915/intel_wakeref.c
> > index dfd87d082218..6bae609e1312 100644
> > --- a/drivers/gpu/drm/i915/intel_wakeref.c
> > +++ b/drivers/gpu/drm/i915/intel_wakeref.c
> > @@ -74,7 +74,7 @@ void __intel_wakeref_put_last(struct intel_wakeref *wf, unsigned long flags)
> >   
> >   	/* Assume we are not in process context and so cannot sleep. */
> >   	if (flags & INTEL_WAKEREF_PUT_ASYNC || !mutex_trylock(&wf->mutex)) {
> > -		mod_delayed_work(system_wq, &wf->work,
> > +		mod_delayed_work(wf->wq, &wf->work,
> >   				 FIELD_GET(INTEL_WAKEREF_PUT_DELAY, flags));
> >   		return;
> >   	}
> > @@ -93,10 +93,10 @@ static void __intel_wakeref_put_work(struct work_struct *wrk)
> >   	____intel_wakeref_put_last(wf);
> >   }
> >   
> > -void __intel_wakeref_init(struct intel_wakeref *wf,
> > -			  struct intel_runtime_pm *rpm,
> > -			  const struct intel_wakeref_ops *ops,
> > -			  struct intel_wakeref_lockclass *key)
> > +int __intel_wakeref_init(struct intel_wakeref *wf,
> > +			 struct intel_runtime_pm *rpm,
> > +			 const struct intel_wakeref_ops *ops,
> > +			 struct intel_wakeref_lockclass *key)
> >   {
> >   	wf->rpm = rpm;
> >   	wf->ops = ops;
> > @@ -105,9 +105,20 @@ void __intel_wakeref_init(struct intel_wakeref *wf,
> >   	atomic_set(&wf->count, 0);
> >   	wf->wakeref = 0;
> >   
> > +	wf->wq = alloc_workqueue("i1915-wakeref", 0, 0);
> 
> Typo here -

Oh, good catch! This is one of my "favorite" typos, for some reason.


>  I wanted to ask however - why does this particular wq 
> "deserves" to be dedicated and can't just use one of the 
> drm_i915_private ones?

It's because there's no easy way to get access to the drm_i915_private
structure from here.  And I don't think this work needs to be in sync
with the rest of the works in i915.

--
Cheers,
Luca.