Re: [Intel-gfx] [PATCH 10/27] drm/i915/guc: Introduce context parent-child relationship

John Harrison
2021-09-13T23:19:18Z

On 8/20/2021 15:44, Matthew Brost wrote:
> Introduce context parent-child relationship. Once this relationship is
> created all pinning / unpinning operations are directed to the parent
> context. The parent context is responsible for pinning all of its'
> children and itself.
>
> This is a precursor to the full GuC multi-lrc implementation but aligns
> to how GuC mutli-lrc interface is defined - a single H2G is used
> register / deregister all of the contexts simultaneously.
>
> Subsequent patches in the series will implement the pinning / unpinning
> operations for parent / child contexts.
>
> v2:
> (Daniel Vetter)
> - Add kernel doc, add wrapper to access parent to ensure safety
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_context.c | 29 ++++++++++++++
> drivers/gpu/drm/i915/gt/intel_context.h | 39 +++++++++++++++++++
> drivers/gpu/drm/i915/gt/intel_context_types.h | 23 +++++++++++
> 3 files changed, 91 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index 508cfe5770c0..00d1aee6d199 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -404,6 +404,8 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
>
> INIT_LIST_HEAD(&ce->destroyed_link);
>
No need for this blank line?

> + INIT_LIST_HEAD(&ce->guc_child_list);
> +
> /*
> * Initialize fence to be complete as this is expected to be complete
> * unless there is a pending schedule disable outstanding.
> @@ -418,10 +420,17 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
>
> void intel_context_fini(struct intel_context *ce)
> {
> + struct intel_context *child, *next;
> +
> if (ce->timeline)
> intel_timeline_put(ce->timeline);
> i915_vm_put(ce->vm);
>
> + /* Need to put the creation ref for the children */
> + if (intel_context_is_parent(ce))
> + for_each_child_safe(ce, child, next)
> + intel_context_put(child);
> +
> mutex_destroy(&ce->pin_mutex);
> i915_active_fini(&ce->active);
> }
> @@ -537,6 +546,26 @@ struct i915_request *intel_context_find_active_request(struct intel_context *ce)
> return active;
> }
>
> +void intel_context_bind_parent_child(struct intel_context *parent,
> + struct intel_context *child)
> +{
> + /*
> + * Callers responsibility to validate that this function is used
> + * correctly but we use GEM_BUG_ON here ensure that they do.
> + */
> + GEM_BUG_ON(!intel_engine_uses_guc(parent->engine));
> + GEM_BUG_ON(intel_context_is_pinned(parent));
> + GEM_BUG_ON(intel_context_is_child(parent));
> + GEM_BUG_ON(intel_context_is_pinned(child));
> + GEM_BUG_ON(intel_context_is_child(child));
> + GEM_BUG_ON(intel_context_is_parent(child));
> +
> + parent->guc_number_children++;
> + list_add_tail(&child->guc_child_link,
> + &parent->guc_child_list);
> + child->parent = parent;
> +}
> +
> #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
> #include "selftest_context.c"
> #endif
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
> index c41098950746..c2985822ab74 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context.h
> @@ -44,6 +44,45 @@ void intel_context_free(struct intel_context *ce);
> int intel_context_reconfigure_sseu(struct intel_context *ce,
> const struct intel_sseu sseu);
>
> +static inline bool intel_context_is_child(struct intel_context *ce)
> +{
> + return !!ce->parent;
> +}
> +
> +static inline bool intel_context_is_parent(struct intel_context *ce)
> +{
> + return !!ce->guc_number_children;
> +}
> +
> +static inline bool intel_context_is_pinned(struct intel_context *ce);
No point declaring 'static inline' if there is no function body?

> +
> +static inline struct intel_context *
> +intel_context_to_parent(struct intel_context *ce)
> +{
> + if (intel_context_is_child(ce)) {
> + /*
> + * The parent holds ref count to the child so it is always safe
> + * for the parent to access the child, but the child has pointer
has pointer -> has a pointer

> + * to the parent without a ref. To ensure this is safe the child
> + * should only access the parent pointer while the parent is
> + * pinned.
> + */
> + GEM_BUG_ON(!intel_context_is_pinned(ce->parent));
> +
> + return ce->parent;
> + } else {
> + return ce;
> + }
> +}
> +
> +void intel_context_bind_parent_child(struct intel_context *parent,
> + struct intel_context *child);
> +
> +#define for_each_child(parent, ce)\
> + list_for_each_entry(ce, &(parent)->guc_child_list, guc_child_link)
> +#define for_each_child_safe(parent, ce, cn)\
> + list_for_each_entry_safe(ce, cn, &(parent)->guc_child_list, guc_child_link)
Do these macros not need some kind of intel_context prefix? Or at least
be 'for_each_guc_child' given the naming of the list/link fields? But
maybe not if the guc_ is dropped from the variable names - see below.

> +
> /**
> * intel_context_lock_pinned - Stablises the 'pinned' status of the HW context
> * @ce - the context
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index fd338a30617e..0fafc178cf2c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -213,6 +213,29 @@ struct intel_context {
> */
> struct list_head destroyed_link;
>
> + /** anonymous struct for parent / children only members */
> + struct {
> + union {
> + /**
> + * @guc_child_list: parent's list of of children
> + * contexts, no protection as immutable after context
> + * creation
> + */
> + struct list_head guc_child_list;
> + /**
> + * @guc_child_link: child's link into parent's list of
> + * children
> + */
> + struct list_head guc_child_link;
> + };
> +
> + /** @parent: pointer to parent if child */
> + struct intel_context *parent;
> +
> + /** @guc_number_children: number of children if parent */
> + u8 guc_number_children;
These are not really a GuC specific fields? The parent/child thing might
only be necessary for GuC submission (although can you say it won't be
required by any future backend, such as the DRM scheduler?) but it is a
context level concept. None of the files changed in this patch are GuC
specific. So no need for 'guc_' prefix? Alternatively, if it all really
is completely GuC specific then the 'parent' field should also have the
prefix? Or even just name the outer struct 'guc_family' or something and
drop the prefixes from all the inner members.

John.

> + };
> +
> #ifdef CONFIG_DRM_I915_SELFTEST
> /**
> * @drop_schedule_enable: Force drop of schedule enable G2H for selftest