Re: [PATCH 3/3] drm/i915: Wait after context init with GuC Submission

[Yu Dai <yu.dai@intel.com>]

Reviewed-by: Alex Dai <yu.dai@intel.com>

On 01/08/2016 07:03 AM, Peter Antoine wrote:
> Per-context initialisation GPU instructions (which are injected directly
> into the ringbuffer rather than being submitted as a batch) should not
> be allowed to mix with user-generated batches in the same submission; it
> will cause confusion for the GuC (which might merge a subsequent
> preemptive request with the non-preemptive initialisation code), and for
> the scheduler, which wouldn't know how to re-inject a non-batch request
> if it were the victim of preemption.
>
> Therefore, we should wait for the initialisation request to complete
> before making the newly-initialised context available for user-mode
> submissions.
>
> Here, we add a call to i915_wait_request() after each existing call to
> i915_add_request_no_flush() (in i915_gem_init_hw(), for the default
> per-engine contexts, and intel_lr_context_deferred_create(), for all
> others).
>
> Adapted from Dave Gordon's patch, which is adapted from Alex's earlier
> patch, which added the wait only to intel_lr_context_render_state_init().
>
> Issue: https://jira01.devtools.intel.com/browse/VIZ-6638
> Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
> Signed-off-by: Peter Antoine <peter.antoine@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_gem.c  | 10 ++++++++++
>   drivers/gpu/drm/i915/intel_lrc.c | 11 +++++++++++
>   2 files changed, 21 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 5be4433..e71bf90 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4847,6 +4847,16 @@ i915_gem_init_hw(struct drm_device *dev)
>   		}
>   
>   		i915_add_request_no_flush(req);
> +
> +		/*
> +		 * GuC firmware will try to collapse its DPC work queue if the
> +		 * new one is for same context. So the following breadcrumb
> +		 * could be amended to this batch and submitted as one batch.
> +		 * Wait here to make sure the context state init is finished
> +		 * before any other submission to GuC.
> +		 */
> +		if (i915.enable_guc_submission)
> +			ret = i915_wait_request(req);
>   	}
>   
>   out:
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 3aa6147..f18fb11 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -2499,6 +2499,17 @@ int intel_lr_context_deferred_alloc(struct intel_context *ctx,
>   			goto error_ringbuf;
>   		}
>   		i915_add_request_no_flush(req);
> +
> +		/*
> +		 * GuC firmware will try to collapse its DPC work queue
> +		 * if the new one is for same context. So the
> +		 * following breadcrumb could be amended to this batch
> +		 * and submitted as one batch. Wait here to make sure
> +		 * the context state init is finished before any other
> +		 * submission to GuC.
> +		 */
> +		if (i915.enable_guc_submission)
> +			ret = i915_wait_request(req);
>   	}
>   	return 0;
>   

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