Re: [PATCH v3 2/3] drm/i915: abolish separate per-ring default_context pointers

[Nick Hoath <nicholas.hoath@xxxxxxxxx>]

On 07/01/2016 10:20, Dave Gordon wrote:
> Now that we've eliminated a lot of uses of ring->default_context,
> we can eliminate the pointer itself.
>
> All the engines share the same default intel_context, so we can just
> keep a single reference to it in the dev_priv structure rather than one
> in each of the engine[] elements. This make refcounting more sensible
> too, as we now have a refcount of one for the one pointer, rather than
> a refcount of one but multiple pointers.
>
>  From an idea by Chris Wilson.
>
> Signed-off-by: Dave Gordon <david.s.gordon@xxxxxxxxx>

Reviewed-by: Nick Hoath <nicholas.hoath@xxxxxxxxx>

> ---
>   drivers/gpu/drm/i915/i915_debugfs.c        |  4 ++--
>   drivers/gpu/drm/i915/i915_drv.h            |  2 ++
>   drivers/gpu/drm/i915/i915_gem.c            |  6 +++---
>   drivers/gpu/drm/i915/i915_gem_context.c    | 22 ++++++++--------------
>   drivers/gpu/drm/i915/i915_gpu_error.c      |  2 +-
>   drivers/gpu/drm/i915/i915_guc_submission.c |  6 +++---
>   drivers/gpu/drm/i915/intel_lrc.c           | 24 +++++++++++++-----------
>   drivers/gpu/drm/i915/intel_ringbuffer.h    |  1 -
>   8 files changed, 32 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 0fc38bb..2613708 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -1943,7 +1943,7 @@ static int i915_context_status(struct seq_file *m, void *unused)
>   		seq_puts(m, "HW context ");
>   		describe_ctx(m, ctx);
>   		for_each_ring(ring, dev_priv, i) {
> -			if (ring->default_context == ctx)
> +			if (dev_priv->kernel_context == ctx)
>   				seq_printf(m, "(default context %s) ",
>   					   ring->name);
>   		}
> @@ -2039,7 +2039,7 @@ static int i915_dump_lrc(struct seq_file *m, void *unused)
>
>   	list_for_each_entry(ctx, &dev_priv->context_list, link) {
>   		for_each_ring(ring, dev_priv, i) {
> -			if (ring->default_context != ctx)
> +			if (dev_priv->kernel_context != ctx)
>   				i915_dump_lrc_obj(m, ring,
>   						  ctx->engine[i].state);
>   		}
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index c2b000a..aef86a8 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1940,6 +1940,8 @@ struct drm_i915_private {
>   		void (*stop_ring)(struct intel_engine_cs *ring);
>   	} gt;
>
> +	struct intel_context *kernel_context;
> +
>   	bool edp_low_vswing;
>
>   	/* perform PHY state sanity checks? */
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index c908ed1..8f101121 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2678,7 +2678,7 @@ void i915_gem_request_free(struct kref *req_ref)
>
>   	if (ctx) {
>   		if (i915.enable_execlists) {
> -			if (ctx != req->ring->default_context)
> +			if (ctx != req->i915->kernel_context)
>   				intel_lr_context_unpin(req);
>   		}
>
> @@ -2774,7 +2774,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
>   	int err;
>
>   	if (ctx == NULL)
> -		ctx = engine->default_context;
> +		ctx = to_i915(engine->dev)->kernel_context;
>   	err = __i915_gem_request_alloc(engine, ctx, &req);
>   	return err ? ERR_PTR(err) : req;
>   }
> @@ -4862,7 +4862,7 @@ i915_gem_init_hw(struct drm_device *dev)
>   	 */
>   	init_unused_rings(dev);
>
> -	BUG_ON(!dev_priv->ring[RCS].default_context);
> +	BUG_ON(!dev_priv->kernel_context);
>
>   	ret = i915_ppgtt_init_hw(dev);
>   	if (ret) {
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index 900ffd0..e1d767e 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -354,11 +354,10 @@ int i915_gem_context_init(struct drm_device *dev)
>   {
>   	struct drm_i915_private *dev_priv = dev->dev_private;
>   	struct intel_context *ctx;
> -	int i;
>
>   	/* Init should only be called once per module load. Eventually the
>   	 * restriction on the context_disabled check can be loosened. */
> -	if (WARN_ON(dev_priv->ring[RCS].default_context))
> +	if (WARN_ON(dev_priv->kernel_context))
>   		return 0;
>
>   	if (intel_vgpu_active(dev) && HAS_LOGICAL_RING_CONTEXTS(dev)) {
> @@ -388,12 +387,7 @@ int i915_gem_context_init(struct drm_device *dev)
>   		return PTR_ERR(ctx);
>   	}
>
> -	for (i = 0; i < I915_NUM_RINGS; i++) {
> -		struct intel_engine_cs *ring = &dev_priv->ring[i];
> -
> -		/* NB: RCS will hold a ref for all rings */
> -		ring->default_context = ctx;
> -	}
> +	dev_priv->kernel_context = ctx;
>
>   	DRM_DEBUG_DRIVER("%s context support initialized\n",
>   			i915.enable_execlists ? "LR" :
> @@ -404,7 +398,7 @@ int i915_gem_context_init(struct drm_device *dev)
>   void i915_gem_context_fini(struct drm_device *dev)
>   {
>   	struct drm_i915_private *dev_priv = dev->dev_private;
> -	struct intel_context *dctx = dev_priv->ring[RCS].default_context;
> +	struct intel_context *dctx = dev_priv->kernel_context;
>   	int i;
>
>   	if (dctx->legacy_hw_ctx.rcs_state) {
> @@ -431,17 +425,17 @@ void i915_gem_context_fini(struct drm_device *dev)
>   		i915_gem_object_ggtt_unpin(dctx->legacy_hw_ctx.rcs_state);
>   	}
>
> -	for (i = 0; i < I915_NUM_RINGS; i++) {
> +	for (i = I915_NUM_RINGS; --i >= 0;) {
>   		struct intel_engine_cs *ring = &dev_priv->ring[i];
>
> -		if (ring->last_context)
> +		if (ring->last_context) {
>   			i915_gem_context_unreference(ring->last_context);
> -
> -		ring->default_context = NULL;
> -		ring->last_context = NULL;
> +			ring->last_context = NULL;
> +		}
>   	}
>
>   	i915_gem_context_unreference(dctx);
> +	dev_priv->kernel_context = NULL;
>   }
>
>   int i915_gem_context_enable(struct drm_i915_gem_request *req)
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index 06ca408..7eeb244 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1050,7 +1050,7 @@ static void i915_gem_record_rings(struct drm_device *dev,
>   			if (request)
>   				rbuf = request->ctx->engine[ring->id].ringbuf;
>   			else
> -				rbuf = ring->default_context->engine[ring->id].ringbuf;
> +				rbuf = dev_priv->kernel_context->engine[ring->id].ringbuf;
>   		} else
>   			rbuf = ring->buffer;
>
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index 9c24424..51ae5c1 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -964,7 +964,7 @@ int i915_guc_submission_enable(struct drm_device *dev)
>   {
>   	struct drm_i915_private *dev_priv = dev->dev_private;
>   	struct intel_guc *guc = &dev_priv->guc;
> -	struct intel_context *ctx = dev_priv->ring[RCS].default_context;
> +	struct intel_context *ctx = dev_priv->kernel_context;
>   	struct i915_guc_client *client;
>
>   	/* client for execbuf submission */
> @@ -1021,7 +1021,7 @@ int intel_guc_suspend(struct drm_device *dev)
>   	if (!i915.enable_guc_submission)
>   		return 0;
>
> -	ctx = dev_priv->ring[RCS].default_context;
> +	ctx = dev_priv->kernel_context;
>
>   	data[0] = HOST2GUC_ACTION_ENTER_S_STATE;
>   	/* any value greater than GUC_POWER_D0 */
> @@ -1047,7 +1047,7 @@ int intel_guc_resume(struct drm_device *dev)
>   	if (!i915.enable_guc_submission)
>   		return 0;
>
> -	ctx = dev_priv->ring[RCS].default_context;
> +	ctx = dev_priv->kernel_context;
>
>   	data[0] = HOST2GUC_ACTION_EXIT_S_STATE;
>   	data[1] = GUC_POWER_D0;
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 8b6542d..aaaa5a3 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -571,7 +571,7 @@ static int execlists_context_queue(struct drm_i915_gem_request *request)
>   	struct drm_i915_gem_request *cursor;
>   	int num_elements = 0;
>
> -	if (request->ctx != ring->default_context)
> +	if (request->ctx != request->i915->kernel_context)
>   		intel_lr_context_pin(request);
>
>   	i915_gem_request_reference(request);
> @@ -664,7 +664,7 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
>
>   	request->ringbuf = request->ctx->engine[request->ring->id].ringbuf;
>
> -	if (request->ctx != request->ring->default_context) {
> +	if (request->ctx != request->i915->kernel_context) {
>   		ret = intel_lr_context_pin(request);
>   		if (ret)
>   			return ret;
> @@ -980,7 +980,7 @@ void intel_execlists_retire_requests(struct intel_engine_cs *ring)
>   		struct drm_i915_gem_object *ctx_obj =
>   				ctx->engine[ring->id].state;
>
> -		if (ctx_obj && (ctx != ring->default_context))
> +		if (ctx_obj && (ctx != req->i915->kernel_context))
>   			intel_lr_context_unpin(req);
>   		list_del(&req->execlist_link);
>   		i915_gem_request_unreference(req);
> @@ -1487,7 +1487,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *ring)
>   	u8 next_context_status_buffer_hw;
>
>   	lrc_setup_hardware_status_page(ring,
> -				ring->default_context->engine[ring->id].state);
> +				dev_priv->kernel_context->engine[ring->id].state);
>
>   	I915_WRITE_IMR(ring, ~(ring->irq_enable_mask | ring->irq_keep_mask));
>   	I915_WRITE(RING_HWSTAM(ring->mmio_base), 0xffffffff);
> @@ -1929,6 +1929,9 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
>
>   static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *ring)
>   {
> +	struct drm_i915_private *dev_priv = to_i915(dev);
> +	struct intel_context *dctx = dev_priv->kernel_context;
> +	int ring_id = ring->id;
>   	int ret;
>
>   	/* Intentionally left blank. */
> @@ -1949,15 +1952,14 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
>   	if (ret)
>   		goto error;
>
> -	ret = intel_lr_context_deferred_alloc(ring->default_context, ring);
> +	ret = intel_lr_context_deferred_alloc(dctx, ring);
>   	if (ret)
>   		goto error;
>
>   	/* As this is the default context, always pin it */
> -	ret = intel_lr_context_do_pin(
> -			ring,
> -			ring->default_context->engine[ring->id].state,
> -			ring->default_context->engine[ring->id].ringbuf);
> +	ret = intel_lr_context_do_pin(ring,
> +				      dctx->engine[ring_id].state,
> +				      dctx->engine[ring_id].ringbuf);
>   	if (ret) {
>   		DRM_ERROR(
>   			"Failed to pin and map ringbuffer %s: %d\n",
> @@ -2388,7 +2390,7 @@ void intel_lr_context_free(struct intel_context *ctx)
>   					ctx->engine[i].ringbuf;
>   			struct intel_engine_cs *ring = ringbuf->ring;
>
> -			if (ctx == ring->default_context) {
> +			if (ctx == ctx->i915->kernel_context) {
>   				intel_unpin_ringbuffer_obj(ringbuf);
>   				i915_gem_object_ggtt_unpin(ctx_obj);
>   			}
> @@ -2507,7 +2509,7 @@ int intel_lr_context_deferred_alloc(struct intel_context *ctx,
>   	ctx->engine[ring->id].ringbuf = ringbuf;
>   	ctx->engine[ring->id].state = ctx_obj;
>
> -	if (ctx != ring->default_context && ring->init_context) {
> +	if (ctx != ctx->i915->kernel_context && ring->init_context) {
>   		struct drm_i915_gem_request *req;
>
>   		req = i915_gem_request_alloc(ring, ctx);
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 49574ff..e950f6c 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -305,7 +305,6 @@ struct  intel_engine_cs {
>
>   	wait_queue_head_t irq_queue;
>
> -	struct intel_context *default_context;
>   	struct intel_context *last_context;
>
>   	struct intel_ring_hangcheck hangcheck;

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