Re: [Intel-gfx] [PATCH 14/27] drm/i915/guc: Assign contexts in parent-child relationship consecutive guc_ids

Matthew Brost
2021-09-15T21:00:43Z

On Wed, Sep 15, 2021 at 01:04:45PM -0700, John Harrison wrote:
> On 8/20/2021 15:44, 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)
> > - Explictly state why we assign consecutive guc_ids
> >
> > 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 | 107 +++++++++++++-----
> > 2 files changed, 86 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > index 023953e77553..3f95b1b4f15c 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > @@ -61,9 +61,13 @@ 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;
> > /** @num_guc_ids: number of guc_ids that can be used */
> > u32 num_guc_ids;
> > /** @max_guc_ids: max number of guc_ids that can be used */
> > 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 00d54bb00bfb..e9dfd43d29a0 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -125,6 +125,18 @@ 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
> The 'hence' clause seems to be attached to the wrong reason. The id space is
> partition because of the contiguous vs random requirements of multi vs
> single LRC, not because a different allocator is used in one partion vs the
> other.
>

Kinda? The reason I partitioned it because to algorithms are different,
we could a unified space with a single algorithm, right? It was just
easier split the space and use 2 already existing data structures rather
cook up an algorithm in a unified space. There isn't a requirement from
the GuC that the space is partitioned, the only requirement is multi-lrc
IDs are contiguous. All this being said, I think comment is correct.

> > + * 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) \
> > + ((guc)->submission_state.num_guc_ids / 16 > 32 ? \
> > + (guc)->submission_state.num_guc_ids / 16 : 32)
> > +
> > /*
> > * Below is a set of functions which control the GuC scheduling state which
> > * require a lock.
> > @@ -1176,6 +1188,10 @@ int intel_guc_submission_init(struct intel_guc *guc)
> > INIT_LIST_HEAD(&guc->submission_state.destroyed_contexts);
> > intel_gt_pm_unpark_work_init(&guc->submission_state.destroyed_worker,
> > destroyed_worker_func);
> > + guc->submission_state.guc_ids_bitmap =
> > + bitmap_zalloc(NUMBER_MULTI_LRC_GUC_ID(guc), GFP_KERNEL);
> > + if (!guc->submission_state.guc_ids_bitmap)
> > + return -ENOMEM;
> > return 0;
> > }
> > @@ -1188,6 +1204,7 @@ 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 void queue_request(struct i915_sched_engine *sched_engine,
> > @@ -1239,18 +1256,43 @@ 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->submission_state.num_guc_ids, 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(guc),
> > + order_base_2(ce->guc_number_children
> > + + 1));
> > + else
> > + ret = ida_simple_get(&guc->submission_state.guc_ids,
> > + NUMBER_MULTI_LRC_GUC_ID(guc),
> > + guc->submission_state.num_guc_ids,
> > + 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->guc_number_children
> > + + 1));
> Is there any check against adding/removing children when the guc_ids are
> allocated? Presumably it shouldn't ever happen but if it did then the

I don't have any protection for that but adding something like this
isn't bad idea.

> bitmap_release would not match the allocation. Maybe add BUG_ON(ce->guc_id)
> to the parent/child link functions (if it's not there already?).
>

Do you something like below in this function?

GEM_BUG_ON(guc_id_not_is_use());

> > + 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);
> > }
> > @@ -1267,49 +1309,60 @@ 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;
> Leaving this as 'ce' and calling the input parameter 'ce_in' would have made
> for significantly easier to read diffs!
>

Yea probably but I think we should change the style to make diff easier
to read.

> > 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));
> > -
> > - list_del_init(&ce->guc_id.link);
> > - guc_id = ce->guc_id.id;
> > + 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));
> > - spin_lock(&ce->guc_state.lock);
> As far as I can tell, the only actual change to this function (beyond
> 'ce_in->id = id' vs 'return id' and adding anti-family asserts) is that this
> spinlock was dropped. However, I'm not seeing any replacement for it or any
> comment about why the spinlock is no longer necessary.
>

Good catch, the lock shouldn't be dropped.

Matt

> John.
>
>
> > - clr_context_registered(ce);
> > - spin_unlock(&ce->guc_state.lock);
> > + list_del_init(&cn->guc_id.link);
> > + ce->guc_id = cn->guc_id;
> > + clr_context_registered(cn);
> > + set_context_guc_id_invalid(cn);
> > - set_context_guc_id_invalid(ce);
> > - return guc_id;
> > + 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;
> > }
> > @@ -1327,7 +1380,7 @@ 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 */
> > @@ -1369,8 +1422,10 @@ 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);
>