Re: [Intel-gfx] [PATCH 10/46] drm/i915/guc: Take engine PM when a context is pinned with GuC submission

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Aug 03, 2021 at 03:29:07PM -0700, Matthew Brost wrote:
> Taking a PM reference to prevent intel_gt_wait_for_idle from short
> circuiting while a scheduling of user context could be enabled.
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/i915/Makefile                 |  1 +
>  .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 36 +++++++++++++++++--
>  2 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index 903de270f2db..5e3a1e2095b0 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -103,6 +103,7 @@ gt-y += \
>  	gt/intel_gt_clock_utils.o \
>  	gt/intel_gt_irq.o \
>  	gt/intel_gt_pm.o \
> +	gt/intel_gt_pm_unpark_work.o \

This file isn't here?

Also pm stuff tends to have very nasty locking requirements, doing special
stuff like this in the backend tends to lead to really big surprises. I
think two options to make sure our locking design stays consistent:
- Lift this to generic code.
- expose some engine_pm_migt_get/put() calls which do have the right set
  of might_lock annoations, and call those in the generic code.

Imo the worst kernel abstractions are those where all implementations
look&act the same, except for locking. Unfortunately i915-gem code is full
of this stuff, and we need to stop this by enlisting lockdep to check the
contracts for us.
-Daniel

>  	gt/intel_gt_pm_irq.o \
>  	gt/intel_gt_requests.o \
>  	gt/intel_gtt.o \
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index 7fe4d1559a81..c5d9548bfd00 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -2056,7 +2056,12 @@ static int guc_context_pre_pin(struct intel_context *ce,
>  
>  static int guc_context_pin(struct intel_context *ce, void *vaddr)
>  {
> -	return __guc_context_pin(ce, ce->engine, vaddr);
> +	int ret = __guc_context_pin(ce, ce->engine, vaddr);
> +
> +	if (likely(!ret && !intel_context_is_barrier(ce)))
> +		intel_engine_pm_get(ce->engine);
> +
> +	return ret;
>  }
>  
>  static void guc_context_unpin(struct intel_context *ce)
> @@ -2067,6 +2072,9 @@ static void guc_context_unpin(struct intel_context *ce)
>  
>  	unpin_guc_id(guc, ce, true);
>  	lrc_unpin(ce);
> +
> +	if (likely(!intel_context_is_barrier(ce)))
> +		intel_engine_pm_put(ce->engine);
>  }
>  
>  static void guc_context_post_unpin(struct intel_context *ce)
> @@ -3002,8 +3010,30 @@ static int guc_virtual_context_pre_pin(struct intel_context *ce,
>  static int guc_virtual_context_pin(struct intel_context *ce, void *vaddr)
>  {
>  	struct intel_engine_cs *engine = guc_virtual_get_sibling(ce->engine, 0);
> +	int ret = __guc_context_pin(ce, engine, vaddr);
> +	intel_engine_mask_t tmp, mask = ce->engine->mask;
> +
> +	if (likely(!ret))
> +		for_each_engine_masked(engine, ce->engine->gt, mask, tmp)
> +			intel_engine_pm_get(engine);
>  
> -	return __guc_context_pin(ce, engine, vaddr);
> +	return ret;
> +}
> +
> +static void guc_virtual_context_unpin(struct intel_context *ce)
> +{
> +	intel_engine_mask_t tmp, mask = ce->engine->mask;
> +	struct intel_engine_cs *engine;
> +	struct intel_guc *guc = ce_to_guc(ce);
> +
> +	GEM_BUG_ON(context_enabled(ce));
> +	GEM_BUG_ON(intel_context_is_barrier(ce));
> +
> +	unpin_guc_id(guc, ce, true);
> +	lrc_unpin(ce);
> +
> +	for_each_engine_masked(engine, ce->engine->gt, mask, tmp)
> +		intel_engine_pm_put(engine);
>  }
>  
>  static void guc_virtual_context_enter(struct intel_context *ce)
> @@ -3040,7 +3070,7 @@ static const struct intel_context_ops virtual_guc_context_ops = {
>  
>  	.pre_pin = guc_virtual_context_pre_pin,
>  	.pin = guc_virtual_context_pin,
> -	.unpin = guc_context_unpin,
> +	.unpin = guc_virtual_context_unpin,
>  	.post_unpin = guc_context_post_unpin,
>  
>  	.ban = guc_context_ban,
> -- 
> 2.28.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch