From 5d9341370f57c058a8d880490ba9e79e761b2d7a Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 31 Jul 2020 09:50:11 +0100 Subject: [PATCH] drm/i915: Export a preallocate variant of i915_active_acquire() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sometimes we have to be very careful not to allocate underneath a mutex (or spinlock) and yet still want to track activity. Enter i915_active_acquire_for_context(). This raises the activity counter on i915_active prior to use and ensures that the fence-tree contains a slot for the context. v2: Refactor active_lookup() so it can be called again before/after locking to resolve contention. Since we protect the rbtree until we idle, we can do a lockfree lookup, with the caveat that if another thread performs a concurrent insertion, the rotations from the insert may cause us to not find our target. A second pass holding the treelock will find the target if it exists, or the place to perform our insertion. Signed-off-by: Chris Wilson Reviewed-by: Thomas Hellström Link: https://patchwork.freedesktop.org/patch/msgid/20200731085015.32368-3-chris@chris-wilson.co.uk Signed-off-by: Rodrigo Vivi Signed-off-by: Joonas Lahtinen --- .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +- drivers/gpu/drm/i915/gt/intel_timeline.c | 4 +- drivers/gpu/drm/i915/i915_active.c | 150 ++++++++++++++---- drivers/gpu/drm/i915/i915_active.h | 12 +- 4 files changed, 130 insertions(+), 38 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c index 90d77cdc6f66..9ce114d67288 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c @@ -1741,7 +1741,7 @@ __parser_mark_active(struct i915_vma *vma, { struct intel_gt_buffer_pool_node *node = vma->private; - return i915_active_ref(&node->active, tl, fence); + return i915_active_ref(&node->active, tl->fence_context, fence); } static int diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c index 4f446534bad0..2baecf414acb 100644 --- a/drivers/gpu/drm/i915/gt/intel_timeline.c +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c @@ -486,7 +486,9 @@ __intel_timeline_get_seqno(struct intel_timeline *tl, * free it after the current request is retired, which ensures that * all writes into the cacheline from previous requests are complete. */ - err = i915_active_ref(&tl->hwsp_cacheline->active, tl, &rq->fence); + err = i915_active_ref(&tl->hwsp_cacheline->active, + tl->fence_context, + &rq->fence); if (err) goto err_cacheline; diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c index 8c6197f8dd0b..9890db303fed 100644 --- a/drivers/gpu/drm/i915/i915_active.c +++ b/drivers/gpu/drm/i915/i915_active.c @@ -28,12 +28,14 @@ static struct i915_global_active { } global; struct active_node { + struct rb_node node; struct i915_active_fence base; struct i915_active *ref; - struct rb_node node; u64 timeline; }; +#define fetch_node(x) rb_entry(READ_ONCE(x), typeof(struct active_node), node) + static inline struct active_node * node_from_active(struct i915_active_fence *active) { @@ -216,12 +218,9 @@ excl_retire(struct dma_fence *fence, struct dma_fence_cb *cb) active_retire(container_of(cb, struct i915_active, excl.cb)); } -static struct i915_active_fence * -active_instance(struct i915_active *ref, struct intel_timeline *tl) +static struct active_node *__active_lookup(struct i915_active *ref, u64 idx) { - struct active_node *node, *prealloc; - struct rb_node **p, *parent; - u64 idx = tl->fence_context; + struct active_node *it; /* * We track the most recently used timeline to skip a rbtree search @@ -230,8 +229,39 @@ active_instance(struct i915_active *ref, struct intel_timeline *tl) * after the previous activity has been retired, or if it matches the * current timeline. */ - node = READ_ONCE(ref->cache); - if (node && node->timeline == idx) + it = READ_ONCE(ref->cache); + if (it && it->timeline == idx) + return it; + + BUILD_BUG_ON(offsetof(typeof(*it), node)); + + /* While active, the tree can only be built; not destroyed */ + GEM_BUG_ON(i915_active_is_idle(ref)); + + it = fetch_node(ref->tree.rb_node); + while (it) { + if (it->timeline < idx) { + it = fetch_node(it->node.rb_right); + } else if (it->timeline > idx) { + it = fetch_node(it->node.rb_left); + } else { + WRITE_ONCE(ref->cache, it); + break; + } + } + + /* NB: If the tree rotated beneath us, we may miss our target. */ + return it; +} + +static struct i915_active_fence * +active_instance(struct i915_active *ref, u64 idx) +{ + struct active_node *node, *prealloc; + struct rb_node **p, *parent; + + node = __active_lookup(ref, idx); + if (likely(node)) return &node->base; /* Preallocate a replacement, just in case */ @@ -268,10 +298,9 @@ active_instance(struct i915_active *ref, struct intel_timeline *tl) rb_insert_color(&node->node, &ref->tree); out: - ref->cache = node; + WRITE_ONCE(ref->cache, node); spin_unlock_irq(&ref->tree_lock); - BUILD_BUG_ON(offsetof(typeof(*node), base)); return &node->base; } @@ -353,63 +382,102 @@ __active_del_barrier(struct i915_active *ref, struct active_node *node) return ____active_del_barrier(ref, node, barrier_to_engine(node)); } -int i915_active_ref(struct i915_active *ref, - struct intel_timeline *tl, - struct dma_fence *fence) +static bool +replace_barrier(struct i915_active *ref, struct i915_active_fence *active) +{ + if (!is_barrier(active)) /* proto-node used by our idle barrier? */ + return false; + + /* + * This request is on the kernel_context timeline, and so + * we can use it to substitute for the pending idle-barrer + * request that we want to emit on the kernel_context. + */ + __active_del_barrier(ref, node_from_active(active)); + return true; +} + +int i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence) { struct i915_active_fence *active; int err; - lockdep_assert_held(&tl->mutex); - /* Prevent reaping in case we malloc/wait while building the tree */ err = i915_active_acquire(ref); if (err) return err; - active = active_instance(ref, tl); + active = active_instance(ref, idx); if (!active) { err = -ENOMEM; goto out; } - if (is_barrier(active)) { /* proto-node used by our idle barrier */ - /* - * This request is on the kernel_context timeline, and so - * we can use it to substitute for the pending idle-barrer - * request that we want to emit on the kernel_context. - */ - __active_del_barrier(ref, node_from_active(active)); + if (replace_barrier(ref, active)) { RCU_INIT_POINTER(active->fence, NULL); atomic_dec(&ref->count); } if (!__i915_active_fence_set(active, fence)) - atomic_inc(&ref->count); + __i915_active_acquire(ref); out: i915_active_release(ref); return err; } -struct dma_fence * -i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f) +static struct dma_fence * +__i915_active_set_fence(struct i915_active *ref, + struct i915_active_fence *active, + struct dma_fence *fence) { struct dma_fence *prev; - /* We expect the caller to manage the exclusive timeline ordering */ - GEM_BUG_ON(i915_active_is_idle(ref)); + if (replace_barrier(ref, active)) { + RCU_INIT_POINTER(active->fence, fence); + return NULL; + } rcu_read_lock(); - prev = __i915_active_fence_set(&ref->excl, f); + prev = __i915_active_fence_set(active, fence); if (prev) prev = dma_fence_get_rcu(prev); else - atomic_inc(&ref->count); + __i915_active_acquire(ref); rcu_read_unlock(); return prev; } +static struct i915_active_fence * +__active_fence(struct i915_active *ref, u64 idx) +{ + struct active_node *it; + + it = __active_lookup(ref, idx); + if (unlikely(!it)) { /* Contention with parallel tree builders! */ + spin_lock_irq(&ref->tree_lock); + it = __active_lookup(ref, idx); + spin_unlock_irq(&ref->tree_lock); + } + GEM_BUG_ON(!it); /* slot must be preallocated */ + + return &it->base; +} + +struct dma_fence * +__i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence) +{ + /* Only valid while active, see i915_active_acquire_for_context() */ + return __i915_active_set_fence(ref, __active_fence(ref, idx), fence); +} + +struct dma_fence * +i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f) +{ + /* We expect the caller to manage the exclusive timeline ordering */ + return __i915_active_set_fence(ref, &ref->excl, f); +} + bool i915_active_acquire_if_busy(struct i915_active *ref) { debug_active_assert(ref); @@ -451,6 +519,24 @@ int i915_active_acquire(struct i915_active *ref) return err; } +int i915_active_acquire_for_context(struct i915_active *ref, u64 idx) +{ + struct i915_active_fence *active; + int err; + + err = i915_active_acquire(ref); + if (err) + return err; + + active = active_instance(ref, idx); + if (!active) { + i915_active_release(ref); + return -ENOMEM; + } + + return 0; /* return with active ref */ +} + void i915_active_release(struct i915_active *ref) { debug_active_assert(ref); @@ -754,7 +840,7 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx) match: rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */ if (p == &ref->cache->node) - ref->cache = NULL; + WRITE_ONCE(ref->cache, NULL); spin_unlock_irq(&ref->tree_lock); return rb_entry(p, struct active_node, node); @@ -809,7 +895,7 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref, */ RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN)); node->base.cb.node.prev = (void *)engine; - atomic_inc(&ref->count); + __i915_active_acquire(ref); } GEM_BUG_ON(rcu_access_pointer(node->base.fence) != ERR_PTR(-EAGAIN)); diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h index cf4058150966..73ded3c52a04 100644 --- a/drivers/gpu/drm/i915/i915_active.h +++ b/drivers/gpu/drm/i915/i915_active.h @@ -163,14 +163,16 @@ void __i915_active_init(struct i915_active *ref, __i915_active_init(ref, active, retire, &__mkey, &__wkey); \ } while (0) -int i915_active_ref(struct i915_active *ref, - struct intel_timeline *tl, - struct dma_fence *fence); +struct dma_fence * +__i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence); +int i915_active_ref(struct i915_active *ref, u64 idx, struct dma_fence *fence); static inline int i915_active_add_request(struct i915_active *ref, struct i915_request *rq) { - return i915_active_ref(ref, i915_request_timeline(rq), &rq->fence); + return i915_active_ref(ref, + i915_request_timeline(rq)->fence_context, + &rq->fence); } struct dma_fence * @@ -198,7 +200,9 @@ int i915_request_await_active(struct i915_request *rq, #define I915_ACTIVE_AWAIT_BARRIER BIT(2) int i915_active_acquire(struct i915_active *ref); +int i915_active_acquire_for_context(struct i915_active *ref, u64 idx); bool i915_active_acquire_if_busy(struct i915_active *ref); + void i915_active_release(struct i915_active *ref); static inline void __i915_active_acquire(struct i915_active *ref)