Re: [PATCH 1/4] drm/i915: Get active pending request for given context

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Hi Tvrtko,

> -----Original Message-----
> From: Tvrtko Ursulin [mailto:tvrtko.ursulin@xxxxxxxxxxxxxxx]
> Sent: Friday, September 21, 2018 6:10 PM
> To: J Karanje, Kedar <kedar.j.karanje@xxxxxxxxx>; intel-
> gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: Diwakar, Praveen <praveen.diwakar@xxxxxxxxx>; Marathe, Yogesh
> <yogesh.marathe@xxxxxxxxx>; Navik, Ankit P <ankit.p.navik@xxxxxxxxx>;
> Muthukumar, Aravindan <aravindan.muthukumar@xxxxxxxxx>
> Subject: Re:  [PATCH 1/4] drm/i915: Get active pending request for
> given context
> 
> 
> On 21/09/2018 10:13, kedar.j.karanje@xxxxxxxxx wrote:
> > From: Praveen Diwakar <praveen.diwakar@xxxxxxxxx>
> >
> > This patch gives us the active pending request count which is yet to
> > be submitted to the GPU
> >
> > Change-Id: I10c2828ad0f1a0b7af147835737134e07a2d5b6d
> > Signed-off-by: Praveen Diwakar <praveen.diwakar@xxxxxxxxx>
> > Signed-off-by: Yogesh Marathe <yogesh.marathe@xxxxxxxxx>
> > Signed-off-by: Aravindan Muthukumar <aravindan.muthukumar@xxxxxxxxx>
> > Signed-off-by: Kedar J Karanje <kedar.j.karanje@xxxxxxxxx>
> > Signed-off-by: Ankit Navik <ankit.p.navik@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/i915_drv.c            | 1 +
> >   drivers/gpu/drm/i915/i915_drv.h            | 5 +++++
> >   drivers/gpu/drm/i915/i915_gem_context.c    | 1 +
> >   drivers/gpu/drm/i915/i915_gem_context.h    | 6 ++++++
> >   drivers/gpu/drm/i915/i915_gem_execbuffer.c | 5 +++++
> >   drivers/gpu/drm/i915/intel_lrc.c           | 6 ++++++
> >   6 files changed, 24 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > b/drivers/gpu/drm/i915/i915_drv.c index f8cfd16..d37c46e 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -903,6 +903,7 @@ static int i915_driver_init_early(struct
> drm_i915_private *dev_priv,
> >   	mutex_init(&dev_priv->av_mutex);
> >   	mutex_init(&dev_priv->wm.wm_mutex);
> >   	mutex_init(&dev_priv->pps_mutex);
> > +	mutex_init(&dev_priv->pred_mutex);
> >
> >   	i915_memcpy_init_early(dev_priv);
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h
> > b/drivers/gpu/drm/i915/i915_drv.h index 4aca534..137ec33 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -1609,6 +1609,11 @@ struct drm_i915_private {
> >   	 * controller on different i2c buses. */
> >   	struct mutex gmbus_mutex;
> >
> > +	/** pred_mutex protects against councurrent usage of pending
> > +	 * request counter for multiple contexts
> > +	 */
> > +	struct mutex pred_mutex;
> > +
> >   	/**
> >   	 * Base address of the gmbus and gpio block.
> >   	 */
> > diff --git a/drivers/gpu/drm/i915/i915_gem_context.c
> > b/drivers/gpu/drm/i915/i915_gem_context.c
> > index b10770c..30932d9 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> > @@ -387,6 +387,7 @@ i915_gem_create_context(struct drm_i915_private
> *dev_priv,
> >   	}
> >
> >   	trace_i915_context_create(ctx);
> > +	ctx->req_cnt = 0;
> >
> >   	return ctx;
> >   }
> > diff --git a/drivers/gpu/drm/i915/i915_gem_context.h
> > b/drivers/gpu/drm/i915/i915_gem_context.h
> > index b116e49..243ea22 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_context.h
> > +++ b/drivers/gpu/drm/i915/i915_gem_context.h
> > @@ -194,6 +194,12 @@ struct i915_gem_context {
> >   	 * context close.
> >   	 */
> >   	struct list_head handles_list;
> > +
> > +	/** req_cnt: tracks the pending commands, based on which we decide
> to
> > +	 * go for low/medium/high load configuration of the GPU, this is
> > +	 * controlled via a mutex
> > +	 */
> > +	u64 req_cnt;
> 
> 64-bit is too wide and mutex causes you problems later in the series.
> I'd suggest atomic_t.
Changes done in v2. 
> 
> >   };
> >
> >   static inline bool i915_gem_context_is_closed(const struct
> > i915_gem_context *ctx) diff --git
> > a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > index 3f0c612..f799ff9 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > @@ -2178,6 +2178,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> >   		       struct drm_syncobj **fences)
> >   {
> >   	struct i915_execbuffer eb;
> > +	struct drm_i915_private *dev_priv = to_i915(dev);
> >   	struct dma_fence *in_fence = NULL;
> >   	struct sync_file *out_fence = NULL;
> >   	int out_fence_fd = -1;
> > @@ -2390,6 +2391,10 @@ i915_gem_do_execbuffer(struct drm_device *dev,
> >   	 */
> >   	eb.request->batch = eb.batch;
> >
> > +	mutex_lock(&dev_priv->pred_mutex);
> > +	eb.ctx->req_cnt++;
> > +	mutex_unlock(&dev_priv->pred_mutex);
> > +
> >   	trace_i915_request_queue(eb.request, eb.batch_flags);
> >   	err = eb_submit(&eb);
> >   err_request:
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c
> > b/drivers/gpu/drm/i915/intel_lrc.c
> > index 1744792..039fbdb 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> > @@ -728,6 +728,12 @@ static void execlists_dequeue(struct intel_engine_cs
> *engine)
> >   			trace_i915_request_in(rq, port_index(port, execlists));
> >   			last = rq;
> >   			submit = true;
> > +
> > +			mutex_lock(&rq->i915->pred_mutex);
> > +			if (rq->gem_context->req_cnt > 0) {
> 
> Presumably you hit underflow here and then added the protection. This was a
> hint the accounting does not work as expected. Preemption for instance would
> wreak havoc with it. :)
> 
> Have a look at my per engine queued/runnable counters for how to do it
> correctly, only that you would need to make it per context and merge into one
> aggregated queued+runnable instead of two separate counters, if you wanted
> to preserve your heuristics.
> 
> https://patchwork.freedesktop.org/patch/227981/
> https://patchwork.freedesktop.org/patch/227976/

We will wait for these patches to get merged and we will continue to investigate
on how to incorporate this in our changes. 

Regards, Ankit
> 
> Regards,
> 
> Tvrtko
> 
> > +				rq->gem_context->req_cnt--;
> > +			}
> > +			mutex_unlock(&rq->i915->pred_mutex);
> >   		}
> >
> >   		rb_erase_cached(&p->node, &execlists->queue);
> >
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