Re: [Intel-gfx] [PATCH 10/26] drm/i915/guc: Assign contexts in parent-child relationship consecutive guc_ids

John Harrison
2021-10-07T22:11:51Z

On 10/4/2021 15:06, Matthew Brost wrote:
> Assign contexts in parent-child relationship consecutive guc_ids. This
> is accomplished by partitioning guc_id space between ones that need to
> be consecutive (1/16 available guc_ids) and ones that do not (15/16 of
> available guc_ids). The consecutive search is implemented via the bitmap
> API.
>
> This is a precursor to the full GuC multi-lrc implementation but aligns
> to how GuC mutli-lrc interface is defined - guc_ids must be consecutive
> when using the GuC multi-lrc interface.
>
> v2:
> (Daniel Vetter)
> - Explicitly state why we assign consecutive guc_ids
> v3:
> (John Harrison)
> - Bring back in spin lock
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
> drivers/gpu/drm/i915/gt/uc/intel_guc.h | 6 +-
> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 104 ++++++++++++++----
> 2 files changed, 86 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> index 25a598e2b6e8..a9f4ec972bfb 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> @@ -76,9 +76,13 @@ struct intel_guc {
> */
> spinlock_t lock;
> /**
> - * @guc_ids: used to allocate new guc_ids
> + * @guc_ids: used to allocate new guc_ids, single-lrc
> */
> struct ida guc_ids;
> + /**
> + * @guc_ids_bitmap: used to allocate new guc_ids, multi-lrc
> + */
> + unsigned long *guc_ids_bitmap;
> /**
> * @guc_id_list: list of intel_context with valid guc_ids but no
> * refs
> 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 1f2809187513..79e7732e83b2 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -128,6 +128,16 @@ guc_create_virtual(struct intel_engine_cs **siblings, unsigned int count);
>
> #define GUC_REQUEST_SIZE 64 /* bytes */
>
> +/*
> + * We reserve 1/16 of the guc_ids for multi-lrc as these need to be contiguous
> + * per the GuC submission interface. A different allocation algorithm is used
> + * (bitmap vs. ida) between multi-lrc and single-lrc hence the reason to
> + * partition the guc_id space. We believe the number of multi-lrc contexts in
> + * use should be low and 1/16 should be sufficient. Minimum of 32 guc_ids for
> + * multi-lrc.
> + */
> +#define NUMBER_MULTI_LRC_GUC_ID (GUC_MAX_LRC_DESCRIPTORS / 16)
> +
> /*
> * Below is a set of functions which control the GuC scheduling state which
> * require a lock.
> @@ -1206,6 +1216,11 @@ int intel_guc_submission_init(struct intel_guc *guc)
> INIT_WORK(&guc->submission_state.destroyed_worker,
> destroyed_worker_func);
>
> + guc->submission_state.guc_ids_bitmap =
> + bitmap_zalloc(NUMBER_MULTI_LRC_GUC_ID, GFP_KERNEL);
> + if (!guc->submission_state.guc_ids_bitmap)
> + return -ENOMEM;
> +
> return 0;
> }
>
> @@ -1217,6 +1232,7 @@ void intel_guc_submission_fini(struct intel_guc *guc)
> guc_lrc_desc_pool_destroy(guc);
> guc_flush_destroyed_contexts(guc);
> i915_sched_engine_put(guc->sched_engine);
> + bitmap_free(guc->submission_state.guc_ids_bitmap);
> }
>
> static inline void queue_request(struct i915_sched_engine *sched_engine,
> @@ -1268,18 +1284,43 @@ static void guc_submit_request(struct i915_request *rq)
> spin_unlock_irqrestore(&sched_engine->lock, flags);
> }
>
> -static int new_guc_id(struct intel_guc *guc)
> +static int new_guc_id(struct intel_guc *guc, struct intel_context *ce)
> {
> - return ida_simple_get(&guc->submission_state.guc_ids, 0,
> - GUC_MAX_LRC_DESCRIPTORS, GFP_KERNEL |
> - __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
> + int ret;
> +
> + GEM_BUG_ON(intel_context_is_child(ce));
> +
> + if (intel_context_is_parent(ce))
> + ret = bitmap_find_free_region(guc->submission_state.guc_ids_bitmap,
> + NUMBER_MULTI_LRC_GUC_ID,
> + order_base_2(ce->parallel.number_children
> + + 1));
> + else
> + ret = ida_simple_get(&guc->submission_state.guc_ids,
> + NUMBER_MULTI_LRC_GUC_ID,
> + GUC_MAX_LRC_DESCRIPTORS,
> + GFP_KERNEL | __GFP_RETRY_MAYFAIL |
> + __GFP_NOWARN);
> + if (unlikely(ret < 0))
> + return ret;
> +
> + ce->guc_id.id = ret;
> + return 0;
> }
>
> static void __release_guc_id(struct intel_guc *guc, struct intel_context *ce)
> {
> + GEM_BUG_ON(intel_context_is_child(ce));
> +
> if (!context_guc_id_invalid(ce)) {
> - ida_simple_remove(&guc->submission_state.guc_ids,
> - ce->guc_id.id);
> + if (intel_context_is_parent(ce))
> + bitmap_release_region(guc->submission_state.guc_ids_bitmap,
> + ce->guc_id.id,
> + order_base_2(ce->parallel.number_children
> + + 1));
There was a discussion on the previous revision about adding a BUG_ON to
ensure that number_children cannot change between the bitmap alloc and
the bitmap release. I'm not seeing the new BUG_ON mentioned in this patch.

John.

> + else
> + ida_simple_remove(&guc->submission_state.guc_ids,
> + ce->guc_id.id);
> reset_lrc_desc(guc, ce->guc_id.id);
> set_context_guc_id_invalid(ce);
> }
> @@ -1296,49 +1337,64 @@ static void release_guc_id(struct intel_guc *guc, struct intel_context *ce)
> spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> }
>
> -static int steal_guc_id(struct intel_guc *guc)
> +static int steal_guc_id(struct intel_guc *guc, struct intel_context *ce)
> {
> - struct intel_context *ce;
> - int guc_id;
> + struct intel_context *cn;
>
> lockdep_assert_held(&guc->submission_state.lock);
> + GEM_BUG_ON(intel_context_is_child(ce));
> + GEM_BUG_ON(intel_context_is_parent(ce));
>
> if (!list_empty(&guc->submission_state.guc_id_list)) {
> - ce = list_first_entry(&guc->submission_state.guc_id_list,
> + cn = list_first_entry(&guc->submission_state.guc_id_list,
> struct intel_context,
> guc_id.link);
>
> - GEM_BUG_ON(atomic_read(&ce->guc_id.ref));
> - GEM_BUG_ON(context_guc_id_invalid(ce));
> + GEM_BUG_ON(atomic_read(&cn->guc_id.ref));
> + GEM_BUG_ON(context_guc_id_invalid(cn));
> + GEM_BUG_ON(intel_context_is_child(cn));
> + GEM_BUG_ON(intel_context_is_parent(cn));
>
> - list_del_init(&ce->guc_id.link);
> - guc_id = ce->guc_id.id;
> + list_del_init(&cn->guc_id.link);
> + ce->guc_id = cn->guc_id;
>
> spin_lock(&ce->guc_state.lock);
> - clr_context_registered(ce);
> + clr_context_registered(cn);
> spin_unlock(&ce->guc_state.lock);
>
> - set_context_guc_id_invalid(ce);
> - return guc_id;
> + set_context_guc_id_invalid(cn);
> +
> + return 0;
> } else {
> return -EAGAIN;
> }
> }
>
> -static int assign_guc_id(struct intel_guc *guc, u16 *out)
> +static int assign_guc_id(struct intel_guc *guc, struct intel_context *ce)
> {
> int ret;
>
> lockdep_assert_held(&guc->submission_state.lock);
> + GEM_BUG_ON(intel_context_is_child(ce));
>
> - ret = new_guc_id(guc);
> + ret = new_guc_id(guc, ce);
> if (unlikely(ret < 0)) {
> - ret = steal_guc_id(guc);
> + if (intel_context_is_parent(ce))
> + return -ENOSPC;
> +
> + ret = steal_guc_id(guc, ce);
> if (ret < 0)
> return ret;
> }
>
> - *out = ret;
> + if (intel_context_is_parent(ce)) {
> + struct intel_context *child;
> + int i = 1;
> +
> + for_each_child(ce, child)
> + child->guc_id.id = ce->guc_id.id + i++;
> + }
> +
> return 0;
> }
>
> @@ -1356,7 +1412,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
> might_lock(&ce->guc_state.lock);
>
> if (context_guc_id_invalid(ce)) {
> - ret = assign_guc_id(guc, &ce->guc_id.id);
> + ret = assign_guc_id(guc, ce);
> if (ret)
> goto out_unlock;
> ret = 1; /* Indidcates newly assigned guc_id */
> @@ -1398,8 +1454,10 @@ static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
> unsigned long flags;
>
> GEM_BUG_ON(atomic_read(&ce->guc_id.ref) < 0);
> + GEM_BUG_ON(intel_context_is_child(ce));
>
> - if (unlikely(context_guc_id_invalid(ce)))
> + if (unlikely(context_guc_id_invalid(ce) ||
> + intel_context_is_parent(ce)))
> return;
>
> spin_lock_irqsave(&guc->submission_state.lock, flags);