[Intel-gfx] [PATCH 2/6] drm/i915: Retire requests along rings
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Tue Apr 24 14:46:49 UTC 2018
On 24/04/2018 14:14, Chris Wilson wrote:
> In the next patch, rings are the central timeline as requests may jump
> between engines. Therefore in the future as we retire in order along the
> engine timeline, we may retire out-of-order within a ring (as the ring now
> occurs along multiple engines), leading to much hilarity in miscomputing
> the position of ring->head.
>
> As an added bonus, retiring along the ring reduces the penalty of having
> one execlists client do cleanup for another (old legacy submission
> shares a ring between all clients). The downside is that slow and
> irregular (off the critical path) process of cleaning up stale requests
> after userspace becomes a modicum less efficient.
>
> In the long run, it will become apparent that the ordered
> ring->request_list matches the ring->timeline, a fun challenge for the
> future will be unifying the two lists to avoid duplication!
>
> v2: We need both engine-order and ring-order processing to maintain our
> knowledge of where individual rings have completed upto as well as
> knowing what was last executing on any engine. And finally by decoupling
> retiring the contexts on the engine and the timelines along the rings,
> we do have to keep a reference to the context on each request
> (previously it was guaranteed by the context being pinned).
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 3 +-
> drivers/gpu/drm/i915/i915_gem.c | 1 +
> drivers/gpu/drm/i915/i915_request.c | 140 +++++++++++-------
> drivers/gpu/drm/i915/i915_utils.h | 6 +
> drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +-
> drivers/gpu/drm/i915/intel_ringbuffer.h | 1 +
> drivers/gpu/drm/i915/selftests/mock_engine.c | 27 +++-
> .../gpu/drm/i915/selftests/mock_gem_device.c | 2 +
> 8 files changed, 120 insertions(+), 66 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 8fd9fb6efba5..1837c01d44d0 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2058,8 +2058,9 @@ struct drm_i915_private {
> void (*resume)(struct drm_i915_private *);
> void (*cleanup_engine)(struct intel_engine_cs *engine);
>
> - struct list_head timelines;
> struct i915_gem_timeline global_timeline;
> + struct list_head timelines;
> + struct list_head rings;
> u32 active_requests;
> u32 request_serial;
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 795ca83aed7a..906e2395c245 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5600,6 +5600,7 @@ int i915_gem_init_early(struct drm_i915_private *dev_priv)
> goto err_dependencies;
>
> mutex_lock(&dev_priv->drm.struct_mutex);
> + INIT_LIST_HEAD(&dev_priv->gt.rings);
> INIT_LIST_HEAD(&dev_priv->gt.timelines);
> err = i915_gem_timeline_init__global(dev_priv);
> mutex_unlock(&dev_priv->drm.struct_mutex);
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index b1993d4a1a53..aa84b5447fd5 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -286,6 +286,7 @@ static int reserve_gt(struct drm_i915_private *i915)
>
> static void unreserve_gt(struct drm_i915_private *i915)
> {
> + GEM_BUG_ON(!i915->gt.active_requests);
> if (!--i915->gt.active_requests)
> i915_gem_park(i915);
> }
> @@ -298,6 +299,7 @@ void i915_gem_retire_noop(struct i915_gem_active *active,
>
> static void advance_ring(struct i915_request *request)
> {
> + struct intel_ring *ring = request->ring;
> unsigned int tail;
>
> /*
> @@ -309,7 +311,8 @@ static void advance_ring(struct i915_request *request)
> * Note this requires that we are always called in request
> * completion order.
> */
> - if (list_is_last(&request->ring_link, &request->ring->request_list)) {
> + GEM_BUG_ON(!list_is_first(&request->ring_link, &ring->request_list));
> + if (list_is_last(&request->ring_link, &ring->request_list)) {
> /*
> * We may race here with execlists resubmitting this request
> * as we retire it. The resubmission will move the ring->tail
> @@ -322,9 +325,9 @@ static void advance_ring(struct i915_request *request)
> } else {
> tail = request->postfix;
> }
> - list_del(&request->ring_link);
> + list_del_init(&request->ring_link);
Why the _init flavour? There are two list heads for being on two
separate lists, but are either path reachable after being removed from
the respective lists? (I may find the answer as I read on.)
>
> - request->ring->head = tail;
> + ring->head = tail;
> }
>
> static void free_capture_list(struct i915_request *request)
> @@ -340,30 +343,79 @@ static void free_capture_list(struct i915_request *request)
> }
> }
>
> +static void __retire_engine_request(struct intel_engine_cs *engine,
> + struct i915_request *request)
> +{
> + GEM_BUG_ON(!i915_request_completed(request));
> +
> + local_irq_disable();
> +
> + spin_lock(&engine->timeline->lock);
> + GEM_BUG_ON(!list_is_first(&request->link, &engine->timeline->requests));
> + list_del_init(&request->link);
> + spin_unlock(&engine->timeline->lock);
> +
> + spin_lock(&request->lock);
> + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags))
> + dma_fence_signal_locked(&request->fence);
> + if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
> + intel_engine_cancel_signaling(request);
> + if (request->waitboost) {
> + GEM_BUG_ON(!atomic_read(&request->i915->gt_pm.rps.num_waiters));
> + atomic_dec(&request->i915->gt_pm.rps.num_waiters);
> + }
> + spin_unlock(&request->lock);
> +
> + local_irq_enable();
> +
> + /*
> + * The backing object for the context is done after switching to the
> + * *next* context. Therefore we cannot retire the previous context until
> + * the next context has already started running. However, since we
> + * cannot take the required locks at i915_request_submit() we
> + * defer the unpinning of the active context to now, retirement of
> + * the subsequent request.
> + */
> + if (engine->last_retired_context)
> + engine->context_unpin(engine, engine->last_retired_context);
> + engine->last_retired_context = request->ctx;
> +}
> +
> +static void __retire_engine_upto(struct intel_engine_cs *engine,
> + struct i915_request *rq)
> +{
> + struct i915_request *tmp;
> +
> + GEM_BUG_ON(!i915_request_completed(rq));
> + if (list_empty(&rq->link))
> + return;
> +
> + do {
> + tmp = list_first_entry(&engine->timeline->requests,
> + typeof(*tmp), link);
> +
> + GEM_BUG_ON(tmp->engine != engine);
> + __retire_engine_request(engine, tmp);
> + } while (tmp != rq);
> +}
> +
> static void i915_request_retire(struct i915_request *request)
> {
> - struct intel_engine_cs *engine = request->engine;
> struct i915_gem_active *active, *next;
>
> GEM_TRACE("%s fence %llx:%d, global=%d, current %d\n",
> - engine->name,
> + request->engine->name,
> request->fence.context, request->fence.seqno,
> request->global_seqno,
> - intel_engine_get_seqno(engine));
> + intel_engine_get_seqno(request->engine));
>
> lockdep_assert_held(&request->i915->drm.struct_mutex);
> GEM_BUG_ON(!i915_sw_fence_signaled(&request->submit));
> GEM_BUG_ON(!i915_request_completed(request));
> - GEM_BUG_ON(!request->i915->gt.active_requests);
>
> trace_i915_request_retire(request);
>
> - spin_lock_irq(&engine->timeline->lock);
> - list_del_init(&request->link);
> - spin_unlock_irq(&engine->timeline->lock);
> -
> advance_ring(request);
> -
> free_capture_list(request);
>
> /*
> @@ -400,49 +452,30 @@ static void i915_request_retire(struct i915_request *request)
> /* Retirement decays the ban score as it is a sign of ctx progress */
> atomic_dec_if_positive(&request->ctx->ban_score);
>
> - /*
> - * The backing object for the context is done after switching to the
> - * *next* context. Therefore we cannot retire the previous context until
> - * the next context has already started running. However, since we
> - * cannot take the required locks at i915_request_submit() we
> - * defer the unpinning of the active context to now, retirement of
> - * the subsequent request.
> - */
> - if (engine->last_retired_context)
> - engine->context_unpin(engine, engine->last_retired_context);
> - engine->last_retired_context = request->ctx;
> -
> - spin_lock_irq(&request->lock);
> - if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags))
> - dma_fence_signal_locked(&request->fence);
> - if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
> - intel_engine_cancel_signaling(request);
> - if (request->waitboost) {
> - GEM_BUG_ON(!atomic_read(&request->i915->gt_pm.rps.num_waiters));
> - atomic_dec(&request->i915->gt_pm.rps.num_waiters);
> - }
> - spin_unlock_irq(&request->lock);
> + __retire_engine_upto(request->engine, request);
>
I did not figure out why do you need to do this. Normally retirement
driven from ring timelines would retire requests on the same engine
belonging to a different ring, as it walks over ring timelines.
Only for direct callers of i915_request_retire it may make a difference
but I don't understand is it an functional difference or just optimisation.
This is then from where list_del_init comes from, since this function
can retire wider than the caller would expect. But then it retires on
the engine (upto) and the callers just walks the list and calls retire
only to find already unlinked elements. Could it just as well then
retire it completely?
> unreserve_gt(request->i915);
>
> i915_sched_node_fini(request->i915, &request->sched);
> +
> + i915_gem_context_put(request->ctx);
> i915_request_put(request);
> }
>
> void i915_request_retire_upto(struct i915_request *rq)
> {
> - struct intel_engine_cs *engine = rq->engine;
> + struct intel_ring *ring = rq->ring;
> struct i915_request *tmp;
>
> lockdep_assert_held(&rq->i915->drm.struct_mutex);
> GEM_BUG_ON(!i915_request_completed(rq));
>
> - if (list_empty(&rq->link))
> + if (list_empty(&rq->ring_link))
> return;
>
> do {
> - tmp = list_first_entry(&engine->timeline->requests,
> - typeof(*tmp), link);
> + tmp = list_first_entry(&ring->request_list,
> + typeof(*tmp), ring_link);
>
> i915_request_retire(tmp);
> } while (tmp != rq);
> @@ -651,9 +684,9 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
> if (ret)
> goto err_unreserve;
>
> - /* Move the oldest request to the slab-cache (if not in use!) */
> - rq = list_first_entry_or_null(&engine->timeline->requests,
> - typeof(*rq), link);
> + /* Move our oldest request to the slab-cache (if not in use!) */
> + rq = list_first_entry_or_null(&ring->request_list,
> + typeof(*rq), ring_link);
This is less efficient now - I wonder if you should still be looking at
the engine timeline here?
> if (rq && i915_request_completed(rq))
> i915_request_retire(rq);
>
> @@ -733,7 +766,7 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
> INIT_LIST_HEAD(&rq->active_list);
> rq->i915 = i915;
> rq->engine = engine;
> - rq->ctx = ctx;
> + rq->ctx = i915_gem_context_get(ctx);
Putting in a short comment saying why the reference is needed would be good.
> rq->ring = ring;
>
> /* No zalloc, must clear what we need by hand */
> @@ -777,6 +810,7 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
>
> err_unwind:
> rq->ring->emit = rq->head;
> + i915_gem_context_put(ctx);
>
> /* Make sure we didn't add ourselves to external state before freeing */
> GEM_BUG_ON(!list_empty(&rq->active_list));
> @@ -1357,38 +1391,30 @@ long i915_request_wait(struct i915_request *rq,
> return timeout;
> }
>
> -static void engine_retire_requests(struct intel_engine_cs *engine)
> +static void ring_retire_requests(struct intel_ring *ring)
> {
> struct i915_request *request, *next;
> - u32 seqno = intel_engine_get_seqno(engine);
> - LIST_HEAD(retire);
>
> - spin_lock_irq(&engine->timeline->lock);
> list_for_each_entry_safe(request, next,
> - &engine->timeline->requests, link) {
> - if (!i915_seqno_passed(seqno, request->global_seqno))
> + &ring->request_list, ring_link) {
> + if (!i915_request_completed(request))
> break;
>
> - list_move_tail(&request->link, &retire);
> - }
> - spin_unlock_irq(&engine->timeline->lock);
> -
> - list_for_each_entry_safe(request, next, &retire, link)
> i915_request_retire(request);
> + }
> }
>
> void i915_retire_requests(struct drm_i915_private *i915)
> {
> - struct intel_engine_cs *engine;
> - enum intel_engine_id id;
> + struct intel_ring *ring, *next;
>
> lockdep_assert_held(&i915->drm.struct_mutex);
>
> if (!i915->gt.active_requests)
> return;
>
> - for_each_engine(engine, i915, id)
> - engine_retire_requests(engine);
> + list_for_each_entry_safe(ring, next, &i915->gt.rings, link)
> + ring_retire_requests(ring);
> }
>
> #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index 0695717522ea..00165ad55fb3 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -120,6 +120,12 @@ static inline u64 ptr_to_u64(const void *ptr)
>
> #include <linux/list.h>
>
> +static inline int list_is_first(const struct list_head *list,
> + const struct list_head *head)
> +{
> + return head->next == list;
> +}
> +
> static inline void __list_del_many(struct list_head *head,
> struct list_head *first)
> {
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index c68ac605b8a9..75dca28782ee 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1065,7 +1065,6 @@ int intel_ring_pin(struct intel_ring *ring,
>
> void intel_ring_reset(struct intel_ring *ring, u32 tail)
> {
> - GEM_BUG_ON(!list_empty(&ring->request_list));
> ring->tail = tail;
> ring->head = tail;
> ring->emit = tail;
> @@ -1124,6 +1123,7 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
>
> GEM_BUG_ON(!is_power_of_2(size));
> GEM_BUG_ON(RING_CTL_SIZE(size) & ~RING_NR_PAGES);
> + lockdep_assert_held(&engine->i915->drm.struct_mutex);
>
> ring = kzalloc(sizeof(*ring), GFP_KERNEL);
> if (!ring)
> @@ -1149,6 +1149,8 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
> }
> ring->vma = vma;
>
> + list_add(&ring->link, &engine->i915->gt.rings);
> +
> return ring;
> }
>
> @@ -1160,6 +1162,8 @@ intel_ring_free(struct intel_ring *ring)
> i915_vma_close(ring->vma);
> __i915_gem_object_release_unless_active(obj);
>
> + list_del(&ring->link);
> +
> kfree(ring);
> }
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index c5e27905b0e1..d816f8dea245 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -129,6 +129,7 @@ struct intel_ring {
> void *vaddr;
>
> struct list_head request_list;
> + struct list_head link;
>
> u32 head;
> u32 tail;
> diff --git a/drivers/gpu/drm/i915/selftests/mock_engine.c b/drivers/gpu/drm/i915/selftests/mock_engine.c
> index 78a89efa1119..a0bc324edadd 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_engine.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_engine.c
> @@ -140,9 +140,18 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
> INIT_LIST_HEAD(&ring->request_list);
> intel_ring_update_space(ring);
>
> + list_add(&ring->link, &engine->i915->gt.rings);
> +
> return ring;
> }
>
> +static void mock_ring_free(struct intel_ring *ring)
> +{
> + list_del(&ring->link);
> +
> + kfree(ring);
> +}
> +
> struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
> const char *name,
> int id)
> @@ -155,12 +164,6 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
> if (!engine)
> return NULL;
>
> - engine->base.buffer = mock_ring(&engine->base);
> - if (!engine->base.buffer) {
> - kfree(engine);
> - return NULL;
> - }
> -
> /* minimal engine setup for requests */
> engine->base.i915 = i915;
> snprintf(engine->base.name, sizeof(engine->base.name), "%s", name);
> @@ -185,7 +188,16 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
> timer_setup(&engine->hw_delay, hw_delay_complete, 0);
> INIT_LIST_HEAD(&engine->hw_queue);
>
> + engine->base.buffer = mock_ring(&engine->base);
> + if (!engine->base.buffer)
> + goto err_breadcrumbs;
> +
> return &engine->base;
> +
> +err_breadcrumbs:
> + intel_engine_fini_breadcrumbs(&engine->base);
> + kfree(engine);
> + return NULL;
> }
>
> void mock_engine_flush(struct intel_engine_cs *engine)
> @@ -219,8 +231,9 @@ void mock_engine_free(struct intel_engine_cs *engine)
> if (engine->last_retired_context)
> engine->context_unpin(engine, engine->last_retired_context);
>
> + mock_ring_free(engine->buffer);
> +
> intel_engine_fini_breadcrumbs(engine);
>
> - kfree(engine->buffer);
> kfree(engine);
> }
> diff --git a/drivers/gpu/drm/i915/selftests/mock_gem_device.c b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> index e6d4b882599a..ac4bacf8b5b9 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> @@ -44,6 +44,7 @@ void mock_device_flush(struct drm_i915_private *i915)
> mock_engine_flush(engine);
>
> i915_retire_requests(i915);
> + GEM_BUG_ON(i915->gt.active_requests);
> }
>
> static void mock_device_release(struct drm_device *dev)
> @@ -224,6 +225,7 @@ struct drm_i915_private *mock_gem_device(void)
> goto err_dependencies;
>
> mutex_lock(&i915->drm.struct_mutex);
> + INIT_LIST_HEAD(&i915->gt.rings);
> INIT_LIST_HEAD(&i915->gt.timelines);
> err = i915_gem_timeline_init__global(i915);
> if (err) {
>
Sorry I did not spot the problem yet. Still in the phase of trying to
understand the approach.
Regards,
Tvrtko
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