[PATCH 16/47] drm/i915/guc: Disable engine barriers with GuC during unpin

[John Harrison]

On 6/24/2021 00:04, Matthew Brost wrote:
> Disable engine barriers for unpinning with GuC. This feature isn't
> needed with the GuC as it disables context scheduling before unpinning
> which guarantees the HW will not reference the context. Hence it is
> not necessary to defer unpinning until a kernel context request
> completes on each engine in the context engine mask.
>
> Cc: John Harrison <john.c.harrison at intel.com>
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_context.c    |  2 +-
>   drivers/gpu/drm/i915/gt/intel_context.h    |  1 +
>   drivers/gpu/drm/i915/gt/selftest_context.c | 10 ++++++++++
>   3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index 1499b8aace2a..7f97753ab164 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -80,7 +80,7 @@ static int intel_context_active_acquire(struct intel_context *ce)
>   
>   	__i915_active_acquire(&ce->active);
>   
> -	if (intel_context_is_barrier(ce))
> +	if (intel_context_is_barrier(ce) || intel_engine_uses_guc(ce->engine))
>   		return 0;
Would be better to have a scheduler flag to say whether barriers are 
required or not. That would prevent polluting front end code with back 
end details.

John.


>   
>   	/* Preallocate tracking nodes */
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
> index 8a7199afbe61..a592a9605dc8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context.h
> @@ -16,6 +16,7 @@
>   #include "intel_engine_types.h"
>   #include "intel_ring_types.h"
>   #include "intel_timeline_types.h"
> +#include "uc/intel_guc_submission.h"
>   
>   #define CE_TRACE(ce, fmt, ...) do {					\
>   	const struct intel_context *ce__ = (ce);			\
> diff --git a/drivers/gpu/drm/i915/gt/selftest_context.c b/drivers/gpu/drm/i915/gt/selftest_context.c
> index 26685b927169..fa7b99a671dd 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_context.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_context.c
> @@ -209,7 +209,13 @@ static int __live_active_context(struct intel_engine_cs *engine)
>   	 * This test makes sure that the context is kept alive until a
>   	 * subsequent idle-barrier (emitted when the engine wakeref hits 0
>   	 * with no more outstanding requests).
> +	 *
> +	 * In GuC submission mode we don't use idle barriers and we instead
> +	 * get a message from the GuC to signal that it is safe to unpin the
> +	 * context from memory.
>   	 */
> +	if (intel_engine_uses_guc(engine))
> +		return 0;
>   
>   	if (intel_engine_pm_is_awake(engine)) {
>   		pr_err("%s is awake before starting %s!\n",
> @@ -357,7 +363,11 @@ static int __live_remote_context(struct intel_engine_cs *engine)
>   	 * on the context image remotely (intel_context_prepare_remote_request),
>   	 * which inserts foreign fences into intel_context.active, does not
>   	 * clobber the idle-barrier.
> +	 *
> +	 * In GuC submission mode we don't use idle barriers.
>   	 */
> +	if (intel_engine_uses_guc(engine))
> +		return 0;
>   
>   	if (intel_engine_pm_is_awake(engine)) {
>   		pr_err("%s is awake before starting %s!\n",