[Intel-gfx] [PATCH 08/12] drm/i915: Split execlist priority queue into rbtree + linked list
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Mon May 15 11:45:16 UTC 2017
On 11/05/2017 20:59, Chris Wilson wrote:
> All the requests at the same priority are executed in FIFO order. They
> do not need to be stored in the rbtree themselves, as they are a simple
> list within a level. If we move the requests at one priority into a list,
> we can then reduce the rbtree to the set of priorities. This should keep
> the height of the rbtree small, as the number of active priorities can not
> exceed the number of active requests and should be typically only a few.
>
> Currently, we have ~2k possible different priority levels, that may
> increase to allow even more fine grained selection. Allocating those in
> advance seems a waste (and may be impossible), so we opt for allocating
> upon first use, and freeing after its requests are depleted. To avoid
> the possibility of an allocation failure causing us to lose a request,
> we preallocate the default priority (0) and bump any request to that
> priority if we fail to allocate it the appropriate plist. Having a
> request (that is ready to run, so not leading to corruption) execute
> out-of-order is better than leaking the request (and its dependency
> tree) entirely.
>
> There should be a benefit to reducing execlists_dequeue() to principally
> using a simple list (and reducing the frequency of both rbtree iteration
> and balancing on erase) but for typical workloads, request coalescing
> should be small enough that we don't notice any change. The main gain is
> from improving PI calls to schedule, and the explicit list within a
> level should make request unwinding simpler (we just need to insert at
> the head of the list rather than the tail and not have to make the
> rbtree search more complicated).
>
> v2: Avoid use-after-free when deleting a depleted priolist
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michał Winiarski <michal.winiarski at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---
> drivers/gpu/drm/i915/i915_debugfs.c | 11 +-
> drivers/gpu/drm/i915/i915_gem_request.c | 4 +-
> drivers/gpu/drm/i915/i915_gem_request.h | 2 +-
> drivers/gpu/drm/i915/i915_guc_submission.c | 50 +++++----
> drivers/gpu/drm/i915/i915_utils.h | 9 ++
> drivers/gpu/drm/i915/intel_lrc.c | 171 ++++++++++++++++++-----------
> drivers/gpu/drm/i915/intel_ringbuffer.h | 7 ++
> 7 files changed, 165 insertions(+), 89 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 9bc86d46a656..6d61a439efd0 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3352,7 +3352,6 @@ static int i915_engine_info(struct seq_file *m, void *unused)
>
> if (i915.enable_execlists) {
> u32 ptr, read, write;
> - struct rb_node *rb;
> unsigned int idx;
>
> seq_printf(m, "\tExeclist status: 0x%08x %08x\n",
> @@ -3396,9 +3395,13 @@ static int i915_engine_info(struct seq_file *m, void *unused)
> rcu_read_unlock();
>
> spin_lock_irq(&engine->timeline->lock);
> - for (rb = engine->execlist_first; rb; rb = rb_next(rb)) {
> - rq = rb_entry(rb, typeof(*rq), priotree.node);
> - print_request(m, rq, "\t\tQ ");
> + for (rb = engine->execlist_first; rb; rb = rb_next(rb)){
> + struct i915_priolist *p =
> + rb_entry(rb, typeof(*p), node);
> +
> + list_for_each_entry(rq, &p->requests,
> + priotree.link)
> + print_request(m, rq, "\t\tQ ");
> }
> spin_unlock_irq(&engine->timeline->lock);
> } else if (INTEL_GEN(dev_priv) > 6) {
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 10361c7e3b37..1ccf2522cdfd 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -159,7 +159,7 @@ i915_priotree_fini(struct drm_i915_private *i915, struct i915_priotree *pt)
> {
> struct i915_dependency *dep, *next;
>
> - GEM_BUG_ON(!RB_EMPTY_NODE(&pt->node));
> + GEM_BUG_ON(!list_empty(&pt->link));
>
> /* Everyone we depended upon (the fences we wait to be signaled)
> * should retire before us and remove themselves from our list.
> @@ -185,7 +185,7 @@ i915_priotree_init(struct i915_priotree *pt)
> {
> INIT_LIST_HEAD(&pt->signalers_list);
> INIT_LIST_HEAD(&pt->waiters_list);
> - RB_CLEAR_NODE(&pt->node);
> + INIT_LIST_HEAD(&pt->link);
> pt->priority = INT_MIN;
> }
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
> index 0ecfc5e2d707..8c508bd9088e 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.h
> +++ b/drivers/gpu/drm/i915/i915_gem_request.h
> @@ -67,7 +67,7 @@ struct i915_dependency {
> struct i915_priotree {
> struct list_head signalers_list; /* those before us, we depend upon */
> struct list_head waiters_list; /* those after us, they depend upon us */
> - struct rb_node node;
> + struct list_head link;
> int priority;
> #define I915_PRIORITY_MAX 1024
> #define I915_PRIORITY_NORMAL 0
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index f069c1faf9a9..440bab856cc2 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -674,32 +674,42 @@ static bool i915_guc_dequeue(struct intel_engine_cs *engine)
>
> spin_lock_irq(&engine->timeline->lock);
> rb = engine->execlist_first;
> + GEM_BUG_ON(rb_first(&engine->execlist_queue) != rb);
> while (rb) {
> - struct drm_i915_gem_request *rq =
> - rb_entry(rb, typeof(*rq), priotree.node);
> -
> - if (last && rq->ctx != last->ctx) {
> - if (port != engine->execlist_port)
> - break;
> -
> - port_assign(port, last);
> - port++;
> + struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> + struct drm_i915_gem_request *rq, *rn;
> +
> + list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
> + if (last && rq->ctx != last->ctx) {
> + if (port != engine->execlist_port) {
> + __list_del_many(&p->requests,
> + &rq->priotree.link);
> + goto done;
> + }
> +
> + port_assign(port, last);
> + port++;
> + }
> +
> + INIT_LIST_HEAD(&rq->priotree.link);
> + rq->priotree.priority = INT_MAX;
> +
> + i915_guc_submit(rq);
> + trace_i915_gem_request_in(rq, port - engine->execlist_port);
> + last = rq;
> + submit = true;
> }
>
> rb = rb_next(rb);
> - rb_erase(&rq->priotree.node, &engine->execlist_queue);
> - RB_CLEAR_NODE(&rq->priotree.node);
> - rq->priotree.priority = INT_MAX;
> -
> - i915_guc_submit(rq);
> - trace_i915_gem_request_in(rq, port - engine->execlist_port);
> - last = rq;
> - submit = true;
> + rb_erase(&p->node, &engine->execlist_queue);
> + INIT_LIST_HEAD(&p->requests);
> + if (p->priority != I915_PRIORITY_NORMAL)
> + kfree(p);
> }
> - if (submit) {
> +done:
> + engine->execlist_first = rb;
> + if (submit)
> port_assign(port, last);
> - engine->execlist_first = rb;
> - }
> spin_unlock_irq(&engine->timeline->lock);
>
> return submit;
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index d9df23795f9a..16ecd1ab108d 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -105,4 +105,13 @@
> __idx; \
> })
>
> +#include <linux/list.h>
> +
> +static inline void __list_del_many(struct list_head *head,
> + struct list_head *first)
> +{
> + first->prev = head;
> + WRITE_ONCE(head->next, first);
> +}
> +
> #endif /* !__I915_UTILS_H */
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 9d789ade1308..849b35796de7 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -436,57 +436,76 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>
> spin_lock_irq(&engine->timeline->lock);
> rb = engine->execlist_first;
> + GEM_BUG_ON(rb_first(&engine->execlist_queue) != rb);
> while (rb) {
> - struct drm_i915_gem_request *cursor =
> - rb_entry(rb, typeof(*cursor), priotree.node);
> -
> - /* Can we combine this request with the current port? It has to
> - * be the same context/ringbuffer and not have any exceptions
> - * (e.g. GVT saying never to combine contexts).
> - *
> - * If we can combine the requests, we can execute both by
> - * updating the RING_TAIL to point to the end of the second
> - * request, and so we never need to tell the hardware about
> - * the first.
> - */
> - if (last && !can_merge_ctx(cursor->ctx, last->ctx)) {
> - /* If we are on the second port and cannot combine
> - * this request with the last, then we are done.
> - */
> - if (port != engine->execlist_port)
> - break;
> -
> - /* If GVT overrides us we only ever submit port[0],
> - * leaving port[1] empty. Note that we also have
> - * to be careful that we don't queue the same
> - * context (even though a different request) to
> - * the second port.
> + struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> + struct drm_i915_gem_request *rq, *rn;
> +
> + list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
> + /*
> + * Can we combine this request with the current port?
> + * It has to be the same context/ringbuffer and not
> + * have any exceptions (e.g. GVT saying never to
> + * combine contexts).
> + *
> + * If we can combine the requests, we can execute both
> + * by updating the RING_TAIL to point to the end of the
> + * second request, and so we never need to tell the
> + * hardware about the first.
> */
> - if (ctx_single_port_submission(last->ctx) ||
> - ctx_single_port_submission(cursor->ctx))
> - break;
> + if (last && !can_merge_ctx(rq->ctx, last->ctx)) {
> + /*
> + * If we are on the second port and cannot
> + * combine this request with the last, then we
> + * are done.
> + */
> + if (port != engine->execlist_port) {
> + __list_del_many(&p->requests,
> + &rq->priotree.link);
> + goto done;
> + }
> +
> + /*
> + * If GVT overrides us we only ever submit
> + * port[0], leaving port[1] empty. Note that we
> + * also have to be careful that we don't queue
> + * the same context (even though a different
> + * request) to the second port.
> + */
> + if (ctx_single_port_submission(last->ctx) ||
> + ctx_single_port_submission(rq->ctx)) {
> + __list_del_many(&p->requests,
> + &rq->priotree.link);
> + goto done;
> + }
> +
> + GEM_BUG_ON(last->ctx == rq->ctx);
> +
> + if (submit)
> + port_assign(port, last);
> + port++;
> + }
>
> - GEM_BUG_ON(last->ctx == cursor->ctx);
> + INIT_LIST_HEAD(&rq->priotree.link);
> + rq->priotree.priority = INT_MAX;
>
> - if (submit)
> - port_assign(port, last);
> - port++;
> + __i915_gem_request_submit(rq);
> + trace_i915_gem_request_in(rq,
> + port - engine->execlist_port);
> + last = rq;
> + submit = true;
> }
>
> rb = rb_next(rb);
> - rb_erase(&cursor->priotree.node, &engine->execlist_queue);
> - RB_CLEAR_NODE(&cursor->priotree.node);
> - cursor->priotree.priority = INT_MAX;
> -
> - __i915_gem_request_submit(cursor);
> - trace_i915_gem_request_in(cursor, port - engine->execlist_port);
> - last = cursor;
> - submit = true;
> + rb_erase(&p->node, &engine->execlist_queue);
> + INIT_LIST_HEAD(&p->requests);
> + if (p->priority != I915_PRIORITY_NORMAL)
> + kfree(p);
> }
> - if (submit) {
> +done:
> + engine->execlist_first = rb;
> + if (submit)
> port_assign(port, last);
> - engine->execlist_first = rb;
> - }
> spin_unlock_irq(&engine->timeline->lock);
>
> if (submit)
> @@ -610,28 +629,53 @@ static void intel_lrc_irq_handler(unsigned long data)
> intel_uncore_forcewake_put(dev_priv, engine->fw_domains);
> }
>
> -static bool insert_request(struct i915_priotree *pt, struct rb_root *root)
> +static bool
> +insert_request(struct intel_engine_cs *engine,
> + struct i915_priotree *pt,
> + int prio)
> {
> - struct rb_node **p, *rb;
> + struct i915_priolist *p;
> + struct rb_node **parent, *rb;
> bool first = true;
>
> +find_priolist:
> /* most positive priority is scheduled first, equal priorities fifo */
> rb = NULL;
> - p = &root->rb_node;
> - while (*p) {
> - struct i915_priotree *pos;
> -
> - rb = *p;
> - pos = rb_entry(rb, typeof(*pos), node);
> - if (pt->priority > pos->priority) {
> - p = &rb->rb_left;
> - } else {
> - p = &rb->rb_right;
> + parent = &engine->execlist_queue.rb_node;
> + while (*parent) {
> + rb = *parent;
> + p = rb_entry(rb, typeof(*p), node);
> + if (prio > p->priority) {
> + parent = &rb->rb_left;
> + } else if (prio < p->priority) {
> + parent = &rb->rb_right;
> first = false;
> + } else {
> + list_add_tail(&pt->link, &p->requests);
> + return false;
> + }
> + }
> +
> + if (prio == I915_PRIORITY_NORMAL) {
> + p = &engine->default_priolist;
> + } else {
> + p = kmalloc(sizeof(*p), GFP_ATOMIC);
I am back to being nervous about this.
I don't see that even with a dedicated slab we can control the number of
spare objects kept around and also cannot turn off the merging. If only
there was something like SLAB_NO_MERGE and kmem_cache_preallocate(cache,
n). With that we would be able to keep some amount of ready objects in
the cache.
As an alternative I was thinking about how hard would it be to keep the
priority levels around even when lists become empty? And only prune from
the shrinker perhaps? Or from the idle worker if we get to some larger
number of priority levels.
Regards,
Tvrtko
> + /* Convert an allocation failure to a priority bump */
> + if (unlikely(!p)) {
> + prio = I915_PRIORITY_NORMAL; /* recurses just once */
> + goto find_priolist;
> }
> }
> - rb_link_node(&pt->node, rb, p);
> - rb_insert_color(&pt->node, root);
> +
> + p->priority = prio;
> + rb_link_node(&p->node, rb, parent);
> + rb_insert_color(&p->node, &engine->execlist_queue);
> +
> + INIT_LIST_HEAD(&p->requests);
> + list_add_tail(&pt->link, &p->requests);
> +
> + if (first)
> + engine->execlist_first = &p->node;
>
> return first;
> }
> @@ -644,12 +688,16 @@ static void execlists_submit_request(struct drm_i915_gem_request *request)
> /* Will be called from irq-context when using foreign fences. */
> spin_lock_irqsave(&engine->timeline->lock, flags);
>
> - if (insert_request(&request->priotree, &engine->execlist_queue)) {
> - engine->execlist_first = &request->priotree.node;
> + if (insert_request(engine,
> + &request->priotree,
> + request->priotree.priority)) {
> if (execlists_elsp_ready(engine))
> tasklet_hi_schedule(&engine->irq_tasklet);
> }
>
> + GEM_BUG_ON(!engine->execlist_first);
> + GEM_BUG_ON(list_empty(&request->priotree.link));
> +
> spin_unlock_irqrestore(&engine->timeline->lock, flags);
> }
>
> @@ -734,10 +782,9 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
> continue;
>
> pt->priority = prio;
> - if (!RB_EMPTY_NODE(&pt->node)) {
> - rb_erase(&pt->node, &engine->execlist_queue);
> - if (insert_request(pt, &engine->execlist_queue))
> - engine->execlist_first = &pt->node;
> + if (!list_empty(&pt->link)) {
> + __list_del_entry(&pt->link);
> + insert_request(engine, pt, prio);
> }
> }
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index c380f3ac8a39..0ca6f5c3f9a7 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -177,6 +177,12 @@ enum intel_engine_id {
> VECS
> };
>
> +struct i915_priolist {
> + struct rb_node node;
> + struct list_head requests;
> + int priority;
> +};
> +
> #define INTEL_ENGINE_CS_MAX_NAME 8
>
> struct intel_engine_cs {
> @@ -367,6 +373,7 @@ struct intel_engine_cs {
>
> /* Execlists */
> struct tasklet_struct irq_tasklet;
> + struct i915_priolist default_priolist;
> struct execlist_port {
> struct drm_i915_gem_request *request_count;
> #define EXECLIST_COUNT_BITS 2
>
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