Re: [Intel-gfx] [PATCH 23/46] drm/i915/guc: Insert submit fences between requests in parent-child relationship

Daniel Vetter
2021-08-09T16:32:49Z

On Tue, Aug 03, 2021 at 03:29:20PM -0700, Matthew Brost wrote:
> The GuC must receive requests in the order submitted for contexts in a
> parent-child relationship to function correctly. To ensure this, insert
> a submit fence between the current request and last request submitted
> for requests / contexts in a parent child relationship. This is
> conceptually similar to a single timeline.
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Cc: John Harrison <John.C.Harrison@Intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_context.c | 2 +
> drivers/gpu/drm/i915/gt/intel_context.h | 5 +
> drivers/gpu/drm/i915/gt/intel_context_types.h | 3 +
> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 3 +-
> drivers/gpu/drm/i915/i915_request.c | 120 ++++++++++++++----
> 5 files changed, 105 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index bb4c14656067..98ef2d0f7a39 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -487,6 +487,8 @@ void intel_context_fini(struct intel_context *ce)
> {
> struct intel_context *child, *next;
>
> + if (ce->last_rq)
> + i915_request_put(ce->last_rq);
> if (ce->timeline)
> intel_timeline_put(ce->timeline);
> i915_vm_put(ce->vm);
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
> index 7ce3b3d2edb7..a302599e436a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context.h
> @@ -60,6 +60,11 @@ intel_context_to_parent(struct intel_context *ce)
> return intel_context_is_child(ce) ? ce->parent : ce;
> }
>
> +static inline bool intel_context_is_parallel(struct intel_context *ce)
> +{
> + return intel_context_is_child(ce) || intel_context_is_parent(ce);
> +}
> +
> void intel_context_bind_parent_child(struct intel_context *parent,
> struct intel_context *child);
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index 9665cb31bab0..f4fc81f64921 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -225,6 +225,9 @@ struct intel_context {
> */
> u8 guc_prio;
> u32 guc_prio_count[GUC_CLIENT_PRIORITY_NUM];
> +
> + /* Last request submitted on a parent */
> + struct i915_request *last_rq;
> };
>
> #endif /* __INTEL_CONTEXT_TYPES__ */
> 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 d1d4a1e59e8d..1cb382f7d79d 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -820,8 +820,7 @@ static inline int rq_prio(const struct i915_request *rq)
>
> static inline bool is_multi_lrc_rq(struct i915_request *rq)
> {
> - return intel_context_is_child(rq->context) ||
> - intel_context_is_parent(rq->context);
> + return intel_context_is_parallel(rq->context);
> }
>
> /*
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index ce446716d092..2e51c8999088 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -1546,36 +1546,62 @@ i915_request_await_object(struct i915_request *to,
> return ret;
> }
>
> +static inline bool is_parallel_rq(struct i915_request *rq)
> +{
> + return intel_context_is_parallel(rq->context);
> +}
> +
> +static inline struct intel_context *request_to_parent(struct i915_request *rq)
> +{
> + return intel_context_to_parent(rq->context);
> +}
> +
> static struct i915_request *
> -__i915_request_add_to_timeline(struct i915_request *rq)
> +__i915_request_ensure_parallel_ordering(struct i915_request *rq,
> + struct intel_timeline *timeline)
> {
> - struct intel_timeline *timeline = i915_request_timeline(rq);
> struct i915_request *prev;
>
> - /*
> - * Dependency tracking and request ordering along the timeline
> - * is special cased so that we can eliminate redundant ordering
> - * operations while building the request (we know that the timeline
> - * itself is ordered, and here we guarantee it).
> - *
> - * As we know we will need to emit tracking along the timeline,
> - * we embed the hooks into our request struct -- at the cost of
> - * having to have specialised no-allocation interfaces (which will
> - * be beneficial elsewhere).
> - *
> - * A second benefit to open-coding i915_request_await_request is
> - * that we can apply a slight variant of the rules specialised
> - * for timelines that jump between engines (such as virtual engines).
> - * If we consider the case of virtual engine, we must emit a dma-fence
> - * to prevent scheduling of the second request until the first is
> - * complete (to maximise our greedy late load balancing) and this
> - * precludes optimising to use semaphores serialisation of a single
> - * timeline across engines.
> - */
> + GEM_BUG_ON(!is_parallel_rq(rq));
> +
> + prev = request_to_parent(rq)->last_rq;
> + if (prev) {
> + if (!__i915_request_is_complete(prev)) {
> + i915_sw_fence_await_sw_fence(&rq->submit,
> + &prev->submit,
> + &rq->submitq);
> +
> + if (rq->engine->sched_engine->schedule)
> + __i915_sched_node_add_dependency(&rq->sched,
> + &prev->sched,
> + &rq->dep,
> + 0);
> + }
> + i915_request_put(prev);
> + }
> +
> + request_to_parent(rq)->last_rq = i915_request_get(rq);
> +
> + return to_request(__i915_active_fence_set(&timeline->last_request,
> + &rq->fence));
> +}
> +
> +static struct i915_request *
> +__i915_request_ensure_ordering(struct i915_request *rq,
> + struct intel_timeline *timeline)
> +{
> + struct i915_request *prev;
> +
> + GEM_BUG_ON(is_parallel_rq(rq));
> +
> prev = to_request(__i915_active_fence_set(&timeline->last_request,
> &rq->fence));
> +
> if (prev && !__i915_request_is_complete(prev)) {
> bool uses_guc = intel_engine_uses_guc(rq->engine);
> + bool pow2 = is_power_of_2(READ_ONCE(prev->engine)->mask |
> + rq->engine->mask);
> + bool same_context = prev->context == rq->context;
>
> /*
> * The requests are supposed to be kept in order. However,
> @@ -1583,13 +1609,11 @@ __i915_request_add_to_timeline(struct i915_request *rq)
> * is used as a barrier for external modification to this
> * context.
> */
> - GEM_BUG_ON(prev->context == rq->context &&
> + GEM_BUG_ON(same_context &&
> i915_seqno_passed(prev->fence.seqno,
> rq->fence.seqno));
>
> - if ((!uses_guc &&
> - is_power_of_2(READ_ONCE(prev->engine)->mask | rq->engine->mask)) ||
> - (uses_guc && prev->context == rq->context))
> + if ((same_context && uses_guc) || (!uses_guc && pow2))
> i915_sw_fence_await_sw_fence(&rq->submit,
> &prev->submit,
> &rq->submitq);
> @@ -1604,6 +1628,50 @@ __i915_request_add_to_timeline(struct i915_request *rq)
> 0);
> }
>
> + return prev;
> +}
> +
> +static struct i915_request *
> +__i915_request_add_to_timeline(struct i915_request *rq)
> +{
> + struct intel_timeline *timeline = i915_request_timeline(rq);
> + struct i915_request *prev;
> +
> + /*
> + * Dependency tracking and request ordering along the timeline
> + * is special cased so that we can eliminate redundant ordering
> + * operations while building the request (we know that the timeline
> + * itself is ordered, and here we guarantee it).
> + *
> + * As we know we will need to emit tracking along the timeline,
> + * we embed the hooks into our request struct -- at the cost of
> + * having to have specialised no-allocation interfaces (which will
> + * be beneficial elsewhere).
> + *
> + * A second benefit to open-coding i915_request_await_request is
> + * that we can apply a slight variant of the rules specialised
> + * for timelines that jump between engines (such as virtual engines).
> + * If we consider the case of virtual engine, we must emit a dma-fence
> + * to prevent scheduling of the second request until the first is
> + * complete (to maximise our greedy late load balancing) and this
> + * precludes optimising to use semaphores serialisation of a single
> + * timeline across engines.
> + *

Can we put a big FIXME in here that this should all be resolved with a
proper interface which passes the entire thing down to the backend?

Or is that no longer (or wasn't ever) the long-term goal?
-Daniel

> + * We do not order parallel submission requests on the timeline as each
> + * parallel submission context has its own timeline and the ordering
> + * rules for parallel requests are that they must be submitted in the
> + * order received from the execbuf IOCTL. So rather than using the
> + * timeline we store a pointer to last request submitted in the
> + * relationship in the gem context and insert a submission fence
> + * between that request and request passed into this function or
> + * alternatively we use completion fence if gem context has a single
> + * timeline and this is the first submission of an execbuf IOCTL.
> + */
> + if (likely(!is_parallel_rq(rq)))
> + prev = __i915_request_ensure_ordering(rq, timeline);
> + else
> + prev = __i915_request_ensure_parallel_ordering(rq, timeline);
> +
> /*
> * Make sure that no request gazumped us - if it was allocated after
> * our i915_request_alloc() and called __i915_request_add() before
> --
> 2.28.0
>

--
Daniel Vetter
Software Engineer, Intel Corporation