Re: [PATCH v6 7/9] drm/i915: Introduce execlist context status change notification

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On to, 2016-06-02 at 12:36 -0400, Zhi Wang wrote:
> This patch introduces an approach to track the execlist context status
> change.
> 
> GVT-g uses GVT context as the "shadow context". The content inside GVT
> context will be copied back to guest after the context is idle. So GVT-g
> has to know the status of the execlist context.
> 
> This function is configurable in the context creation service. Currently,
> Only GVT-g will create the "status-change-notification" enabled GEM
> context.
> 
> v6:
> 
> - When !CONFIG_DRM_I915_GVT, make GVT code as dead code then compiler
> could automatically eliminate them for us. (Chris)
> - Always initialize the notifier header, so it could be switched on/off
> at runtime. (Chris)
> 
> v5:
> 
> - Only compile this feature when CONFIG_DRM_I915_GVT is enabled.(Tvrtko)
> 
> Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h  |  2 ++
>  drivers/gpu/drm/i915/intel_lrc.c | 24 ++++++++++++++++++++++++
>  drivers/gpu/drm/i915/intel_lrc.h |  5 +++++
>  3 files changed, 31 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index f6cb60a..dee72d3 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -877,9 +877,11 @@ struct i915_gem_context {
>  		u64 lrc_desc;
>  		int pin_count;
>  		bool initialised;
> +		struct atomic_notifier_head status_notifier;

I think this could be outside engine block, just one per context.

>  	} engine[I915_NUM_ENGINES];
>  	u32 lrc_ring_buffer_size;
>  	u32 lrc_addressing_mode_bits;
> +	bool enable_lrc_status_change_notification;
>  
>  	struct list_head link;
>  
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index ffb436c..96d20c8 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -404,6 +404,22 @@ static void execlists_submit_requests(struct drm_i915_gem_request *rq0,
>  	spin_unlock_irq(&dev_priv->uncore.lock);
>  }
>  
> +static inline void execlists_context_status_change(
> +		struct drm_i915_gem_request *rq,
> +		unsigned long status)
> +{
> +	/* The compiler should be fine with the dead-code elimination */

The comment could rather be "Currently, only GVT-g code uses status
notifications" :)

> +	if (!IS_ENABLED(CONFIG_DRM_I915_GVT))
> +		return;
> +
> +	if (!rq->ctx->enable_lrc_status_change_notification)
> +		return;
> +

I think above line should be dropped, just don't register notifier for
context that does not want notifications, and if the chain is empty, no
call is made.

> +	atomic_notifier_call_chain(
> +			&rq->ctx->engine[rq->engine->id].status_notifier,
> +			status, rq);
> +}
> +
>  static void execlists_context_unqueue(struct intel_engine_cs *engine)
>  {
>  	struct drm_i915_gem_request *req0 = NULL, *req1 = NULL;
> @@ -439,6 +455,11 @@ static void execlists_context_unqueue(struct intel_engine_cs *engine)
>  	if (unlikely(!req0))
>  		return;
>  
> +	execlists_context_status_change(req0, CONTEXT_SCHEDULE_IN);
> +
> +	if (req1)
> +		execlists_context_status_change(req1, CONTEXT_SCHEDULE_IN);
> +
>  	if (req0->elsp_submitted & engine->idle_lite_restore_wa) {
>  		/*
>  		 * WaIdleLiteRestore: make sure we never cause a lite restore
> @@ -477,6 +498,8 @@ execlists_check_remove_request(struct intel_engine_cs *engine, u32 ctx_id)
>  	if (--head_req->elsp_submitted > 0)
>  		return 0;
>  
> +	execlists_context_status_change(head_req, CONTEXT_SCHEDULE_OUT);
> +
>  	list_del(&head_req->execlist_link);
>  	i915_gem_request_unreference(head_req);
>  
> @@ -2489,6 +2512,7 @@ static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
>  	ce->ringbuf = ringbuf;
>  	ce->state = ctx_obj;
>  	ce->initialised = engine->init_context == NULL;
> +	ATOMIC_INIT_NOTIFIER_HEAD(&ce->status_notifier);
>  
>  	return 0;
>  
> diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
> index e133c33..7a7ae8d 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.h
> +++ b/drivers/gpu/drm/i915/intel_lrc.h
> @@ -68,6 +68,11 @@ enum {
>  #define GEN8_CSB_READ_PTR(csb_status) \
>  	(((csb_status) & GEN8_CSB_READ_PTR_MASK) >> 8)
>  
> +enum {
> +	CONTEXT_SCHEDULE_IN = 0,
> +	CONTEXT_SCHEDULE_OUT,
> +};
> +

Again, prefixes? At least INTEL_

With above;

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas

>  /* Logical Rings */
>  int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request);
>  int intel_logical_ring_reserve_space(struct drm_i915_gem_request *request);
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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