Re: [Intel-gfx] [PATCH 17/27] drm/i915/guc: Implement multi-lrc reset

Matthew Brost
2021-09-22T16:23:52Z

On Mon, Sep 20, 2021 at 03:44:18PM -0700, John Harrison wrote:
> On 8/20/2021 15:44, Matthew Brost wrote:
>
> Update context and full GPU reset to work with multi-lrc. The idea is
> parent context tracks all the active requests inflight for itself and
> its' children. The parent context owns the reset replaying / canceling
>
> its' -> its
>
>
> requests as needed.
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_context.c | 11 ++--
> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 63 +++++++++++++------
> 2 files changed, 51 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index 00d1aee6d199..5615be32879c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -528,20 +528,21 @@ struct i915_request *intel_context_create_request(struct intel_context *ce)
>
> struct i915_request *intel_context_find_active_request(struct intel_context *ce)
> {
> + struct intel_context *parent = intel_context_to_parent(ce);
> struct i915_request *rq, *active = NULL;
> unsigned long flags;
>
> GEM_BUG_ON(!intel_engine_uses_guc(ce->engine));
>
> Should this not check the parent as well/instead?
>

I don't think so. The 'ce' could be a not parallel context, a parent
context, or a child context.

> And to be clear, this can be called on regular contexts (where ce == parent)
> and on both the parent or child contexts of multi-LRC contexts (where ce may or
> may not match parent)?
>

Right. The parent owns the parent->guc_state.lock/requests and search
that list for the first non-completed request that matches submitted
'ce'.

>
>
>
> - spin_lock_irqsave(&ce->guc_state.lock, flags);
> - list_for_each_entry_reverse(rq, &ce->guc_state.requests,
> + spin_lock_irqsave(&parent->guc_state.lock, flags);
> + list_for_each_entry_reverse(rq, &parent->guc_state.requests,
> sched.link) {
> - if (i915_request_completed(rq))
> + if (i915_request_completed(rq) && rq->context == ce)
>
> 'rq->context == ce' means:
>
> 1. single-LRC context, rq is owned by ce
> 2. multi-LRC context, ce is child, rq really belongs to ce but is being
> tracked by parent
> 3. multi-LRC context, ce is parent, rq really is owned by ce
>
> So when 'rq->ce != ce', it means that the request is owned by a different child
> to 'ce' but within the same multi-LRC group. So we want to ignore that request
> and keep searching until we find one that is really owned by the target ce?
>

All correct.

>
> break;
>
> - active = rq;
> + active = (rq->context == ce) ? rq : active;
>
> Would be clearer to say 'if(rq->ce != ce) continue;' and leave 'active = rq;'
> alone?
>

Yes, that is probably cleaner.

> And again, the intention is to ignore requests that are owned by other members
> of the same multi-LRC group?
>
> Would be good to add some documentation to this function to explain the above
> (assuming my description is correct?).
>

Will add a comment explaining this.

>
> }
> - spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> + spin_unlock_irqrestore(&parent->guc_state.lock, flags);
>
> return active;
> }
> 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 f0b60fecf253..e34e0ea9136a 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -670,6 +670,11 @@ static int rq_prio(const struct i915_request *rq)
> return rq->sched.attr.priority;
> }
>
> +static inline bool is_multi_lrc(struct intel_context *ce)
> +{
> + return intel_context_is_parallel(ce);
> +}
> +
> static bool is_multi_lrc_rq(struct i915_request *rq)
> {
> return intel_context_is_parallel(rq->context);
> @@ -1179,10 +1184,13 @@ __unwind_incomplete_requests(struct intel_context *ce)
>
> static void __guc_reset_context(struct intel_context *ce, bool stalled)
> {
> + bool local_stalled;
> struct i915_request *rq;
> unsigned long flags;
> u32 head;
> + int i, number_children = ce->guc_number_children;
>
> If this is a child context, does it not need to pull the child count from the
> parent? Likewise the list/link pointers below? Or does each child context have
> a full list of its siblings + parent?
>

This function shouldn't be called by a child. Will add
GEM_BUG_ON(intel_context_is_child(ce)) to this function.

>
> bool skip = false;
> + struct intel_context *parent = ce;
>
> intel_context_get(ce);
>
> @@ -1209,25 +1217,34 @@ static void __guc_reset_context(struct intel_context *ce, bool stalled)
> if (unlikely(skip))
> goto out_put;
>
> - rq = intel_context_find_active_request(ce);
> - if (!rq) {
> - head = ce->ring->tail;
> - stalled = false;
> - goto out_replay;
> - }
> + for (i = 0; i < number_children + 1; ++i) {
> + if (!intel_context_is_pinned(ce))
> + goto next_context;
> +
> + local_stalled = false;
> + rq = intel_context_find_active_request(ce);
> + if (!rq) {
> + head = ce->ring->tail;
> + goto out_replay;
> + }
>
> - if (!i915_request_started(rq))
> - stalled = false;
> + GEM_BUG_ON(i915_active_is_idle(&ce->active));
> + head = intel_ring_wrap(ce->ring, rq->head);
>
> - GEM_BUG_ON(i915_active_is_idle(&ce->active));
> - head = intel_ring_wrap(ce->ring, rq->head);
> - __i915_request_reset(rq, stalled);
> + if (i915_request_started(rq))
>
> Why change the ordering of the started test versus the wrap/reset call? Is it
> significant? Why is it now important to be reversed?
>

Off the top of my head I'm not sure what the ordering is changed. I'll
have to double check on this.

>
> + local_stalled = true;
>
> + __i915_request_reset(rq, local_stalled && stalled);
> out_replay:
> - guc_reset_state(ce, head, stalled);
> - __unwind_incomplete_requests(ce);
> + guc_reset_state(ce, head, local_stalled && stalled);
> +next_context:
> + if (i != number_children)
> + ce = list_next_entry(ce, guc_child_link);
>
> Can this not be put in to the step clause of the for statement?
>

Maybe? Does list_next_entry blow up on that last entry? Idk? If not,
then yes this can be added to the loop. Will double check on this.

>
> + }
> +
> + __unwind_incomplete_requests(parent);
> out_put:
> - intel_context_put(ce);
> + intel_context_put(parent);
>
> As above, I think this function would benefit from some comments to explain
> exactly what is being done and why.
>

Sure. Will add some comments.

Matt

> John.
>
>
> }
>
> void intel_guc_submission_reset(struct intel_guc *guc, bool stalled)
> @@ -1248,7 +1265,8 @@ void intel_guc_submission_reset(struct intel_guc *guc, bool stalled)
>
> xa_unlock(&guc->context_lookup);
>
> - if (intel_context_is_pinned(ce))
> + if (intel_context_is_pinned(ce) &&
> + !intel_context_is_child(ce))
> __guc_reset_context(ce, stalled);
>
> intel_context_put(ce);
> @@ -1340,7 +1358,8 @@ void intel_guc_submission_cancel_requests(struct intel_guc *guc)
>
> xa_unlock(&guc->context_lookup);
>
> - if (intel_context_is_pinned(ce))
> + if (intel_context_is_pinned(ce) &&
> + !intel_context_is_child(ce))
> guc_cancel_context_requests(ce);
>
> intel_context_put(ce);
> @@ -2031,6 +2050,8 @@ static struct i915_sw_fence *guc_context_block(struct intel_context *ce)
> u16 guc_id;
> bool enabled;
>
> + GEM_BUG_ON(intel_context_is_child(ce));
> +
> spin_lock_irqsave(&ce->guc_state.lock, flags);
>
> incr_context_blocked(ce);
> @@ -2068,6 +2089,7 @@ static void guc_context_unblock(struct intel_context *ce)
> bool enable;
>
> GEM_BUG_ON(context_enabled(ce));
> + GEM_BUG_ON(intel_context_is_child(ce));
>
> spin_lock_irqsave(&ce->guc_state.lock, flags);
>
> @@ -2099,11 +2121,14 @@ static void guc_context_unblock(struct intel_context *ce)
> static void guc_context_cancel_request(struct intel_context *ce,
> struct i915_request *rq)
> {
> + struct intel_context *block_context =
> + request_to_scheduling_context(rq);
> +
> if (i915_sw_fence_signaled(&rq->submit)) {
> struct i915_sw_fence *fence;
>
> intel_context_get(ce);
> - fence = guc_context_block(ce);
> + fence = guc_context_block(block_context);
> i915_sw_fence_wait(fence);
> if (!i915_request_completed(rq)) {
> __i915_request_skip(rq);
> @@ -2117,7 +2142,7 @@ static void guc_context_cancel_request(struct intel_context *ce,
> */
> flush_work(&ce_to_guc(ce)->ct.requests.worker);
>
> - guc_context_unblock(ce);
> + guc_context_unblock(block_context);
> intel_context_put(ce);
> }
> }
> @@ -2143,6 +2168,8 @@ static void guc_context_ban(struct intel_context *ce, struct i915_request *rq)
> intel_wakeref_t wakeref;
> unsigned long flags;
>
> + GEM_BUG_ON(intel_context_is_child(ce));
> +
> guc_flush_submissions(guc);
>
> spin_lock_irqsave(&ce->guc_state.lock, flags);
>
>
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