Re: [Intel-gfx] [PATCH 12/27] drm/i915/guc: Add multi-lrc context registration

John Harrison
2021-09-15T19:21:52Z

On 8/20/2021 15:44, Matthew Brost wrote:
> Add multi-lrc context registration H2G. In addition a workqueue and
> process descriptor are setup during multi-lrc context registration as
> these data structures are needed for multi-lrc submission.
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_context_types.h | 12 ++
> drivers/gpu/drm/i915/gt/intel_lrc.c | 5 +
> drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h | 2 +-
> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 109 +++++++++++++++++-
> 4 files changed, 126 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index 0fafc178cf2c..6f567ebeb039 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -232,8 +232,20 @@ struct intel_context {
> /** @parent: pointer to parent if child */
> struct intel_context *parent;
>
> +
> + /** @guc_wqi_head: head pointer in work queue */
> + u16 guc_wqi_head;
> + /** @guc_wqi_tail: tail pointer in work queue */
> + u16 guc_wqi_tail;
> +
These should be in the 'guc_state' sub-struct? Would be good to keep all
GuC specific content in one self-contained struct. Especially given the
other child/parent fields are no going to be guc_ prefixed any more.

> /** @guc_number_children: number of children if parent */
> u8 guc_number_children;
> +
> + /**
> + * @parent_page: page in context used by parent for work queue,
Maybe 'page in context record'? Otherwise, exactly what 'context' is
meant here? It isn't the 'struct intel_context'. The contetx record is
saved as 'ce->state' / 'ce->lrc_reg_state', yes? Is it possible to link
to either of those field? Probably not given that they don't appear to
have any kerneldoc description :(. Maybe add that in too :).

> + * work queue descriptor
Later on, it is described as 'process descriptor and work queue'. It
would be good to be consistent.

> + */
> + u8 parent_page;
> };
>
> #ifdef CONFIG_DRM_I915_SELFTEST
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index bb4af4977920..0ddbad4e062a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -861,6 +861,11 @@ __lrc_alloc_state(struct intel_context *ce, struct intel_engine_cs *engine)
> context_size += PAGE_SIZE;
> }
>
> + if (intel_context_is_parent(ce)) {
> + ce->parent_page = context_size / PAGE_SIZE;
> + context_size += PAGE_SIZE;
> + }
> +
> obj = i915_gem_object_create_lmem(engine->i915, context_size, 0);
> if (IS_ERR(obj))
> obj = i915_gem_object_create_shmem(engine->i915, context_size);
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
> index fa4be13c8854..0e600a3b8f1e 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
> @@ -52,7 +52,7 @@
>
> #define GUC_DOORBELL_INVALID 256
>
> -#define GUC_WQ_SIZE (PAGE_SIZE * 2)
> +#define GUC_WQ_SIZE (PAGE_SIZE / 2)
Is this size actually dictated by the GuC API? Or is it just a driver
level decision? If the latter, shouldn't this be below instead?

>
> /* Work queue item header definitions */
> #define WQ_STATUS_ACTIVE 1
> 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 14b24298cdd7..dbcb9ab28a9a 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -340,6 +340,39 @@ static struct i915_priolist *to_priolist(struct rb_node *rb)
> return rb_entry(rb, struct i915_priolist, node);
> }
>
> +/*
> + * When using multi-lrc submission an extra page in the context state is
> + * reserved for the process descriptor and work queue.
> + *
> + * The layout of this page is below:
> + * 0 guc_process_desc
> + * ... unused
> + * PAGE_SIZE / 2 work queue start
> + * ... work queue
> + * PAGE_SIZE - 1 work queue end
> + */
> +#define WQ_OFFSET (PAGE_SIZE / 2)
Can this not be derived from GUC_WQ_SIZE given that the two are
fundamentally linked? E.g. '#define WQ_OFFSET (PAGE_SIZE -
GUC_WQ_SIZE)'? And maybe have a '#define WQ_TOTAL_SIZE PAGE_SIZE' and
use that in all of WQ_OFFSET, GUC_WQ_SIZE and the allocation itself in
intel_lrc.c?

Also, the process descriptor is actually an array of descriptors sized
by the number of children? Or am I misunderstanding the code below? In
so, shouldn't there be a 'COMPILE_BUG_ON((MAX_ENGINE_INSTANCE *
sizeof(descriptor)) < (WQ_DESC_SIZE)' where WQ_DESC_SIZE is
WQ_TOTAL_SIZE - WQ_SIZE?

> +static u32 __get_process_desc_offset(struct intel_context *ce)
> +{
> + GEM_BUG_ON(!ce->parent_page);
> +
> + return ce->parent_page * PAGE_SIZE;
> +}
> +
> +static u32 __get_wq_offset(struct intel_context *ce)
> +{
> + return __get_process_desc_offset(ce) + WQ_OFFSET;
> +}
> +
> +static struct guc_process_desc *
> +__get_process_desc(struct intel_context *ce)
> +{
> + return (struct guc_process_desc *)
> + (ce->lrc_reg_state +
> + ((__get_process_desc_offset(ce) -
> + LRC_STATE_OFFSET) / sizeof(u32)));
Where did the LRC_STATE_OFFSET come from? Is that built in to the
lrg_reg_state pointer itself? That needs to be documented somewhere.

> +}
> +
> static struct guc_lrc_desc *__get_lrc_desc(struct intel_guc *guc, u32 index)
> {
> struct guc_lrc_desc *base = guc->lrc_desc_pool_vaddr;
> @@ -1342,6 +1375,30 @@ static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
> spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> }
>
> +static int __guc_action_register_multi_lrc(struct intel_guc *guc,
> + struct intel_context *ce,
> + u32 guc_id,
> + u32 offset,
> + bool loop)
> +{
> + struct intel_context *child;
> + u32 action[4 + MAX_ENGINE_INSTANCE];
> + int len = 0;
> +
> + GEM_BUG_ON(ce->guc_number_children > MAX_ENGINE_INSTANCE);
> +
> + action[len++] = INTEL_GUC_ACTION_REGISTER_CONTEXT_MULTI_LRC;
> + action[len++] = guc_id;
> + action[len++] = ce->guc_number_children + 1;
> + action[len++] = offset;
> + for_each_child(ce, child) {
> + offset += sizeof(struct guc_lrc_desc);
> + action[len++] = offset;
> + }
> +
> + return guc_submission_send_busy_loop(guc, action, len, 0, loop);
> +}
> +
> static int __guc_action_register_context(struct intel_guc *guc,
> u32 guc_id,
> u32 offset,
> @@ -1364,9 +1421,15 @@ static int register_context(struct intel_context *ce, bool loop)
> ce->guc_id.id * sizeof(struct guc_lrc_desc);
> int ret;
>
> + GEM_BUG_ON(intel_context_is_child(ce));
> trace_intel_context_register(ce);
>
> - ret = __guc_action_register_context(guc, ce->guc_id.id, offset, loop);
> + if (intel_context_is_parent(ce))
> + ret = __guc_action_register_multi_lrc(guc, ce, ce->guc_id.id,
> + offset, loop);
> + else
> + ret = __guc_action_register_context(guc, ce->guc_id.id, offset,
> + loop);
> if (likely(!ret)) {
> unsigned long flags;
>
> @@ -1396,6 +1459,7 @@ static int deregister_context(struct intel_context *ce, u32 guc_id, bool loop)
> {
> struct intel_guc *guc = ce_to_guc(ce);
>
> + GEM_BUG_ON(intel_context_is_child(ce));
> trace_intel_context_deregister(ce);
>
> return __guc_action_deregister_context(guc, guc_id, loop);
> @@ -1423,6 +1487,7 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
> struct guc_lrc_desc *desc;
> bool context_registered;
> intel_wakeref_t wakeref;
> + struct intel_context *child;
> int ret = 0;
>
> GEM_BUG_ON(!engine->mask);
> @@ -1448,6 +1513,42 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
> desc->context_flags = CONTEXT_REGISTRATION_FLAG_KMD;
> guc_context_policy_init(engine, desc);
>
> + /*
> + * Context is a parent, we need to register a process descriptor
> + * describing a work queue and register all child contexts.
Technically, this should say 'If the context is a parent'. Or just move
it to be inside the if block.

> + */
> + if (intel_context_is_parent(ce)) {
> + struct guc_process_desc *pdesc;
> +
> + ce->guc_wqi_tail = 0;
> + ce->guc_wqi_head = 0;
> +
> + desc->process_desc = i915_ggtt_offset(ce->state) +
> + __get_process_desc_offset(ce);
> + desc->wq_addr = i915_ggtt_offset(ce->state) +
> + __get_wq_offset(ce);
> + desc->wq_size = GUC_WQ_SIZE;
> +
> + pdesc = __get_process_desc(ce);
> + memset(pdesc, 0, sizeof(*(pdesc)));
> + pdesc->stage_id = ce->guc_id.id;
> + pdesc->wq_base_addr = desc->wq_addr;
> + pdesc->wq_size_bytes = desc->wq_size;
> + pdesc->priority = GUC_CLIENT_PRIORITY_KMD_NORMAL;
Should this not be inherited from the ce? And same below. Or are we not
using this priority in that way?

John.

> + pdesc->wq_status = WQ_STATUS_ACTIVE;
> +
> + for_each_child(ce, child) {
> + desc = __get_lrc_desc(guc, child->guc_id.id);
> +
> + desc->engine_class =
> + engine_class_to_guc_class(engine->class);
> + desc->hw_context_desc = child->lrc.lrca;
> + desc->priority = GUC_CLIENT_PRIORITY_KMD_NORMAL;
> + desc->context_flags = CONTEXT_REGISTRATION_FLAG_KMD;
> + guc_context_policy_init(engine, desc);
> + }
> + }
> +
> /*
> * The context_lookup xarray is used to determine if the hardware
> * context is currently registered. There are two cases in which it
> @@ -2858,6 +2959,12 @@ g2h_context_lookup(struct intel_guc *guc, u32 desc_idx)
> return NULL;
> }
>
> + if (unlikely(intel_context_is_child(ce))) {
> + drm_err(&guc_to_gt(guc)->i915->drm,
> + "Context is child, desc_idx %u", desc_idx);
> + return NULL;
> + }
> +
> return ce;
> }
>