Re: [Intel-gfx] [PATCH 02/26] drm/i915/guc: Take GT PM ref when deregistering context

Matthew Brost
2021-10-08T01:33:05Z

On Wed, Oct 06, 2021 at 08:37:03PM -0700, John Harrison wrote:
> On 10/4/2021 15:06, Matthew Brost wrote:
> > Taking a PM reference to prevent intel_gt_wait_for_idle from short
> > circuiting while a deregister context H2G is in flight. To do this must
> > issue the deregister H2G from a worker as context can be destroyed from
> > an atomic context and taking GT PM ref blows up. Previously we took a
> > runtime PM from this atomic context which worked but will stop working
> > once runtime pm autosuspend in enabled.
> >
> > So this patch is two fold, stop intel_gt_wait_for_idle from short
> > circuting and fix runtime pm autosuspend.
> >
> > v2:
> > (John Harrison)
> > - Split structure changes out in different patch
> > (Tvrtko)
> > - Don't drop lock in deregister_destroyed_contexts
> >
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> > drivers/gpu/drm/i915/gt/intel_context.c | 2 +
> > drivers/gpu/drm/i915/gt/intel_context_types.h | 7 +
> > drivers/gpu/drm/i915/gt/intel_engine_pm.h | 5 +
> > drivers/gpu/drm/i915/gt/intel_gt_pm.h | 4 +
> > drivers/gpu/drm/i915/gt/uc/intel_guc.h | 11 ++
> > .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 146 +++++++++++-------
> > 6 files changed, 121 insertions(+), 54 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> > index e9a0cad5c34d..1076066f41e0 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> > @@ -399,6 +399,8 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
> > ce->guc_id.id = GUC_INVALID_LRC_ID;
> > INIT_LIST_HEAD(&ce->guc_id.link);
> > + INIT_LIST_HEAD(&ce->destroyed_link);
> > +
> > /*
> > * Initialize fence to be complete as this is expected to be complete
> > * unless there is a pending schedule disable outstanding.
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> > index e7e3984aab78..4613d027cbc3 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> > @@ -213,6 +213,13 @@ struct intel_context {
> > struct list_head link;
> > } guc_id;
> > + /**
> > + * @destroyed_link: link in guc->submission_state.destroyed_contexts, in
> > + * list when context is pending to be destroyed (deregistered with the
> > + * GuC), protected by guc->submission_state.lock
> > + */
> > + struct list_head destroyed_link;
> > +
> > #ifdef CONFIG_DRM_I915_SELFTEST
> > /**
> > * @drop_schedule_enable: Force drop of schedule enable G2H for selftest
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.h b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
> > index 8520c595f5e1..6fdeae668e6e 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
> > @@ -16,6 +16,11 @@ intel_engine_pm_is_awake(const struct intel_engine_cs *engine)
> > return intel_wakeref_is_active(&engine->wakeref);
> > }
> > +static inline void __intel_engine_pm_get(struct intel_engine_cs *engine)
> > +{
> > + __intel_wakeref_get(&engine->wakeref);
> > +}
> > +
> > static inline void intel_engine_pm_get(struct intel_engine_cs *engine)
> > {
> > intel_wakeref_get(&engine->wakeref);
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.h b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
> > index d0588d8aaa44..05de6c1af25b 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
> > @@ -41,6 +41,10 @@ static inline void intel_gt_pm_put_async(struct intel_gt *gt)
> > intel_wakeref_put_async(&gt->wakeref);
> > }
> > +#define with_intel_gt_pm(gt, tmp) \
> > + for (tmp = 1, intel_gt_pm_get(gt); tmp; \
> > + intel_gt_pm_put(gt), tmp = 0)
> > +
> > static inline int intel_gt_pm_wait_for_idle(struct intel_gt *gt)
> > {
> > return intel_wakeref_wait_for_idle(&gt->wakeref);
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > index 65b5e8eeef96..25a598e2b6e8 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > @@ -84,6 +84,17 @@ struct intel_guc {
> > * refs
> > */
> > struct list_head guc_id_list;
> > + /**
> > + * @destroyed_contexts: list of contexts waiting to be destroyed
> > + * (deregistered with the GuC)
> > + */
> > + struct list_head destroyed_contexts;
> > + /**
> > + * @destroyed_worker: worker to deregister contexts, need as we
> > + * need to take a GT PM reference and can't from destroy
> > + * function as it might be in an atomic context (no sleeping)
> > + */
> > + struct work_struct destroyed_worker;
> > } submission_state;
> > /**
> > 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 ad5c18119d92..17da2fea1bff 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -90,8 +90,8 @@
> > * used for all of GuC submission but that could change in the future.
> > *
> > * guc->submission_state.lock
> > - * Protects guc_id allocation for the given GuC, i.e. only one context can be
> > - * doing guc_id allocation operations at a time for each GuC in the system.
> > + * Global lock for GuC submission state. Protects guc_ids and destroyed contexts
> > + * list.
> Feels like this should not be removing explanations, only adding to them.
> The patch itself is only adding new features not removing them. Either the
> details about id allocation are not worth mentioning and should not have
> been added in the previous patch. Or they are and should be kept rather than
> removed in this patch. Either way works for me. The comment was valid
> information but does maybe count as obvious from the guc_id member (and
> friends) are within a per GuC instance structure.
>

The comment before this patch is already in drm-tip merged in a patch
prior to this series. Prior to this patch, this lock was very specific
to guc_id allocation now it is a generic global submission lock. The
explaination has been updated to reflect that.

Matt

> > *
> > * ce->guc_state.lock
> > * Protects everything under ce->guc_state. Ensures that a context is in the
> > @@ -719,6 +719,7 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
> > if (deregister)
> > guc_signal_context_fence(ce);
> > if (destroyed) {
> > + intel_gt_pm_put_async(guc_to_gt(guc));
> > release_guc_id(guc, ce);
> > __guc_context_destroy(ce);
> > }
> > @@ -797,6 +798,8 @@ static void guc_flush_submissions(struct intel_guc *guc)
> > spin_unlock_irqrestore(&sched_engine->lock, flags);
> > }
> > +static void guc_flush_destroyed_contexts(struct intel_guc *guc);
> > +
> > void intel_guc_submission_reset_prepare(struct intel_guc *guc)
> > {
> > int i;
> > @@ -815,6 +818,7 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
> > spin_unlock_irq(&guc_to_gt(guc)->irq_lock);
> > guc_flush_submissions(guc);
> > + guc_flush_destroyed_contexts(guc);
> > /*
> > * Handle any outstanding G2Hs before reset. Call IRQ handler directly
> > @@ -1126,6 +1130,8 @@ void intel_guc_submission_reset_finish(struct intel_guc *guc)
> > intel_gt_unpark_heartbeats(guc_to_gt(guc));
> > }
> > +static void destroyed_worker_func(struct work_struct *w);
> > +
> > /*
> > * Set up the memory resources to be shared with the GuC (via the GGTT)
> > * at firmware loading time.
> > @@ -1151,6 +1157,9 @@ int intel_guc_submission_init(struct intel_guc *guc)
> > spin_lock_init(&guc->submission_state.lock);
> > INIT_LIST_HEAD(&guc->submission_state.guc_id_list);
> > ida_init(&guc->submission_state.guc_ids);
> > + INIT_LIST_HEAD(&guc->submission_state.destroyed_contexts);
> > + INIT_WORK(&guc->submission_state.destroyed_worker,
> > + destroyed_worker_func);
> > return 0;
> > }
> > @@ -1161,6 +1170,7 @@ void intel_guc_submission_fini(struct intel_guc *guc)
> > return;
> > guc_lrc_desc_pool_destroy(guc);
> > + guc_flush_destroyed_contexts(guc);
> Seems like these lines should be reversed. We should destroy the higher
> level constructs before the lower level ones that they could be built on.
>
> > i915_sched_engine_put(guc->sched_engine);
> > }
> > @@ -1859,11 +1869,30 @@ static void guc_context_sched_disable(struct intel_context *ce)
> > static inline void guc_lrc_desc_unpin(struct intel_context *ce)
> > {
> > struct intel_guc *guc = ce_to_guc(ce);
> > + struct intel_gt *gt = guc_to_gt(guc);
> > + unsigned long flags;
> > + bool disabled;
> > + GEM_BUG_ON(!intel_gt_pm_is_awake(gt));
> > GEM_BUG_ON(!lrc_desc_registered(guc, ce->guc_id.id));
> > GEM_BUG_ON(ce != __get_context(guc, ce->guc_id.id));
> > GEM_BUG_ON(context_enabled(ce));
> > + /* Seal race with Reset */
> > + spin_lock_irqsave(&ce->guc_state.lock, flags);
> > + disabled = submission_disabled(guc);
> > + if (likely(!disabled)) {
> > + __intel_gt_pm_get(gt);
> > + set_context_destroyed(ce);
> > + clr_context_registered(ce);
> > + }
> > + spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > + if (unlikely(disabled)) {
> > + release_guc_id(guc, ce);
> > + __guc_context_destroy(ce);
> > + return;
> > + }
> > +
> > deregister_context(ce, ce->guc_id.id);
> > }
> > @@ -1891,78 +1920,86 @@ static void __guc_context_destroy(struct intel_context *ce)
> > }
> > }
> > +static void guc_flush_destroyed_contexts(struct intel_guc *guc)
> > +{
> > + struct intel_context *ce, *cn;
> > + unsigned long flags;
> > +
> > + GEM_BUG_ON(!submission_disabled(guc) &&
> > + guc_submission_initialized(guc));
> > +
> > + spin_lock_irqsave(&guc->submission_state.lock, flags);
> > + list_for_each_entry_safe(ce, cn,
> > + &guc->submission_state.destroyed_contexts,
> > + destroyed_link) {
> > + list_del_init(&ce->destroyed_link);
> > + __release_guc_id(guc, ce);
> > + __guc_context_destroy(ce);
> > + }
> > + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > +}
> > +
> > +static void deregister_destroyed_contexts(struct intel_guc *guc)
> > +{
> > + struct intel_context *ce, *cn;
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&guc->submission_state.lock, flags);
> > + list_for_each_entry_safe(ce, cn,
> > + &guc->submission_state.destroyed_contexts,
> > + destroyed_link) {
> > + list_del_init(&ce->destroyed_link);
> > + guc_lrc_desc_unpin(ce);
> > + }
> > + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > +}
> > +
> > +static void destroyed_worker_func(struct work_struct *w)
> > +{
> > + struct intel_guc *guc = container_of(w, struct intel_guc,
> > + submission_state.destroyed_worker);
> > + struct intel_gt *gt = guc_to_gt(guc);
> > + int tmp;
> > +
> > + with_intel_gt_pm(gt, tmp)
> > + deregister_destroyed_contexts(guc);
> > +}
> > +
> > static void guc_context_destroy(struct kref *kref)
> > {
> > struct intel_context *ce = container_of(kref, typeof(*ce), ref);
> > - struct intel_runtime_pm *runtime_pm = ce->engine->uncore->rpm;
> > struct intel_guc *guc = ce_to_guc(ce);
> > - intel_wakeref_t wakeref;
> > unsigned long flags;
> > - bool disabled;
> > + bool destroy;
> > /*
> > * If the guc_id is invalid this context has been stolen and we can free
> > * it immediately. Also can be freed immediately if the context is not
> > * registered with the GuC or the GuC is in the middle of a reset.
> > */
> > - if (context_guc_id_invalid(ce)) {
> > - __guc_context_destroy(ce);
> > - return;
> > - } else if (submission_disabled(guc) ||
> > - !lrc_desc_registered(guc, ce->guc_id.id)) {
> > - release_guc_id(guc, ce);
> > - __guc_context_destroy(ce);
> > - return;
> > - }
> > -
> > - /*
> > - * We have to acquire the context spinlock and check guc_id again, if it
> > - * is valid it hasn't been stolen and needs to be deregistered. We
> > - * delete this context from the list of unpinned guc_id available to
> > - * steal to seal a race with guc_lrc_desc_pin(). When the G2H CTB
> > - * returns indicating this context has been deregistered the guc_id is
> > - * returned to the pool of available guc_id.
> > - */
> > spin_lock_irqsave(&guc->submission_state.lock, flags);
> > - if (context_guc_id_invalid(ce)) {
> > - spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > - __guc_context_destroy(ce);
> > - return;
> > + destroy = submission_disabled(guc) || context_guc_id_invalid(ce) ||
> > + !lrc_desc_registered(guc, ce->guc_id.id);
> > + if (likely(!destroy)) {
> > + if (!list_empty(&ce->guc_id.link))
> > + list_del_init(&ce->guc_id.link);
> > + list_add_tail(&ce->destroyed_link,
> > + &guc->submission_state.destroyed_contexts);
> > + } else {
> > + __release_guc_id(guc, ce);
> 'destroy' can be true if the guc_id is invalid. Is it good to call release
> on an invalid id?
>
> John.
>
> > }
> > -
> > - if (!list_empty(&ce->guc_id.link))
> > - list_del_init(&ce->guc_id.link);
> > spin_unlock_irqrestore(&guc->submission_state.lock, flags);
> > -
> > - /* Seal race with Reset */
> > - spin_lock_irqsave(&ce->guc_state.lock, flags);
> > - disabled = submission_disabled(guc);
> > - if (likely(!disabled)) {
> > - set_context_destroyed(ce);
> > - clr_context_registered(ce);
> > - }
> > - spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > - if (unlikely(disabled)) {
> > - release_guc_id(guc, ce);
> > + if (unlikely(destroy)) {
> > __guc_context_destroy(ce);
> > return;
> > }
> > /*
> > - * We defer GuC context deregistration until the context is destroyed
> > - * in order to save on CTBs. With this optimization ideally we only need
> > - * 1 CTB to register the context during the first pin and 1 CTB to
> > - * deregister the context when the context is destroyed. Without this
> > - * optimization, a CTB would be needed every pin & unpin.
> > - *
> > - * XXX: Need to acqiure the runtime wakeref as this can be triggered
> > - * from context_free_worker when runtime wakeref is not held.
> > - * guc_lrc_desc_unpin requires the runtime as a GuC register is written
> > - * in H2G CTB to deregister the context. A future patch may defer this
> > - * H2G CTB if the runtime wakeref is zero.
> > + * We use a worker to issue the H2G to deregister the context as we can
> > + * take the GT PM for the first time which isn't allowed from an atomic
> > + * context.
> > */
> > - with_intel_runtime_pm(runtime_pm, wakeref)
> > - guc_lrc_desc_unpin(ce);
> > + queue_work(system_unbound_wq, &guc->submission_state.destroyed_worker);
> > }
> > static int guc_context_alloc(struct intel_context *ce)
> > @@ -2798,6 +2835,7 @@ int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
> > intel_context_put(ce);
> > } else if (context_destroyed(ce)) {
> > /* Context has been destroyed */
> > + intel_gt_pm_put_async(guc_to_gt(guc));
> > release_guc_id(guc, ce);
> > __guc_context_destroy(ce);
> > }
>