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author | Chris Wilson <chris@chris-wilson.co.uk> | 2019-02-05 13:00:05 +0000 |
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committer | Chris Wilson <chris@chris-wilson.co.uk> | 2019-02-05 17:20:11 +0000 |
commit | 21950ee7cc8f13c5350bda0cae22cdb7ac7e3058 (patch) | |
tree | 83c07ae5da83aa7ef95c5f8821b5ab8cf2b7dd08 /drivers/gpu/drm/i915/i915_request.h | |
parent | 5f5c139d6900b3338963bddcd8a567dcad33cf92 (diff) | |
download | linux-stable-21950ee7cc8f13c5350bda0cae22cdb7ac7e3058.tar.gz linux-stable-21950ee7cc8f13c5350bda0cae22cdb7ac7e3058.tar.bz2 linux-stable-21950ee7cc8f13c5350bda0cae22cdb7ac7e3058.zip |
drm/i915: Pull i915_gem_active into the i915_active family
Looking forward, we need to break the struct_mutex dependency on
i915_gem_active. In the meantime, external use of i915_gem_active is
quite beguiling, little do new users suspect that it implies a barrier
as each request it tracks must be ordered wrt the previous one. As one
of many, it can be used to track activity across multiple timelines, a
shared fence, which fits our unordered request submission much better. We
need to steer external users away from the singular, exclusive fence
imposed by i915_gem_active to i915_active instead. As part of that
process, we move i915_gem_active out of i915_request.c into
i915_active.c to start separating the two concepts, and rename it to
i915_active_request (both to tie it to the concept of tracking just one
request, and to give it a longer, less appealing name).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190205130005.2807-5-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers/gpu/drm/i915/i915_request.h')
-rw-r--r-- | drivers/gpu/drm/i915/i915_request.h | 383 |
1 files changed, 0 insertions, 383 deletions
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h index 3cffb96203b9..40f3e8dcbdd5 100644 --- a/drivers/gpu/drm/i915/i915_request.h +++ b/drivers/gpu/drm/i915/i915_request.h @@ -403,387 +403,4 @@ static inline void i915_request_mark_complete(struct i915_request *rq) void i915_retire_requests(struct drm_i915_private *i915); -/* - * We treat requests as fences. This is not be to confused with our - * "fence registers" but pipeline synchronisation objects ala GL_ARB_sync. - * We use the fences to synchronize access from the CPU with activity on the - * GPU, for example, we should not rewrite an object's PTE whilst the GPU - * is reading them. We also track fences at a higher level to provide - * implicit synchronisation around GEM objects, e.g. set-domain will wait - * for outstanding GPU rendering before marking the object ready for CPU - * access, or a pageflip will wait until the GPU is complete before showing - * the frame on the scanout. - * - * In order to use a fence, the object must track the fence it needs to - * serialise with. For example, GEM objects want to track both read and - * write access so that we can perform concurrent read operations between - * the CPU and GPU engines, as well as waiting for all rendering to - * complete, or waiting for the last GPU user of a "fence register". The - * object then embeds a #i915_gem_active to track the most recent (in - * retirement order) request relevant for the desired mode of access. - * The #i915_gem_active is updated with i915_gem_active_set() to track the - * most recent fence request, typically this is done as part of - * i915_vma_move_to_active(). - * - * When the #i915_gem_active completes (is retired), it will - * signal its completion to the owner through a callback as well as mark - * itself as idle (i915_gem_active.request == NULL). The owner - * can then perform any action, such as delayed freeing of an active - * resource including itself. - */ -struct i915_gem_active; - -typedef void (*i915_gem_retire_fn)(struct i915_gem_active *, - struct i915_request *); - -struct i915_gem_active { - struct i915_request __rcu *request; - struct list_head link; - i915_gem_retire_fn retire; -}; - -void i915_gem_retire_noop(struct i915_gem_active *, - struct i915_request *request); - -/** - * init_request_active - prepares the activity tracker for use - * @active - the active tracker - * @func - a callback when then the tracker is retired (becomes idle), - * can be NULL - * - * init_request_active() prepares the embedded @active struct for use as - * an activity tracker, that is for tracking the last known active request - * associated with it. When the last request becomes idle, when it is retired - * after completion, the optional callback @func is invoked. - */ -static inline void -init_request_active(struct i915_gem_active *active, - i915_gem_retire_fn retire) -{ - RCU_INIT_POINTER(active->request, NULL); - INIT_LIST_HEAD(&active->link); - active->retire = retire ?: i915_gem_retire_noop; -} - -/** - * i915_gem_active_set - updates the tracker to watch the current request - * @active - the active tracker - * @request - the request to watch - * - * i915_gem_active_set() watches the given @request for completion. Whilst - * that @request is busy, the @active reports busy. When that @request is - * retired, the @active tracker is updated to report idle. - */ -static inline void -i915_gem_active_set(struct i915_gem_active *active, - struct i915_request *request) -{ - list_move(&active->link, &request->active_list); - rcu_assign_pointer(active->request, request); -} - -/** - * i915_gem_active_set_retire_fn - updates the retirement callback - * @active - the active tracker - * @fn - the routine called when the request is retired - * @mutex - struct_mutex used to guard retirements - * - * i915_gem_active_set_retire_fn() updates the function pointer that - * is called when the final request associated with the @active tracker - * is retired. - */ -static inline void -i915_gem_active_set_retire_fn(struct i915_gem_active *active, - i915_gem_retire_fn fn, - struct mutex *mutex) -{ - lockdep_assert_held(mutex); - active->retire = fn ?: i915_gem_retire_noop; -} - -static inline struct i915_request * -__i915_gem_active_peek(const struct i915_gem_active *active) -{ - /* - * Inside the error capture (running with the driver in an unknown - * state), we want to bend the rules slightly (a lot). - * - * Work is in progress to make it safer, in the meantime this keeps - * the known issue from spamming the logs. - */ - return rcu_dereference_protected(active->request, 1); -} - -/** - * i915_gem_active_raw - return the active request - * @active - the active tracker - * - * i915_gem_active_raw() returns the current request being tracked, or NULL. - * It does not obtain a reference on the request for the caller, so the caller - * must hold struct_mutex. - */ -static inline struct i915_request * -i915_gem_active_raw(const struct i915_gem_active *active, struct mutex *mutex) -{ - return rcu_dereference_protected(active->request, - lockdep_is_held(mutex)); -} - -/** - * i915_gem_active_peek - report the active request being monitored - * @active - the active tracker - * - * i915_gem_active_peek() returns the current request being tracked if - * still active, or NULL. It does not obtain a reference on the request - * for the caller, so the caller must hold struct_mutex. - */ -static inline struct i915_request * -i915_gem_active_peek(const struct i915_gem_active *active, struct mutex *mutex) -{ - struct i915_request *request; - - request = i915_gem_active_raw(active, mutex); - if (!request || i915_request_completed(request)) - return NULL; - - return request; -} - -/** - * i915_gem_active_get - return a reference to the active request - * @active - the active tracker - * - * i915_gem_active_get() returns a reference to the active request, or NULL - * if the active tracker is idle. The caller must hold struct_mutex. - */ -static inline struct i915_request * -i915_gem_active_get(const struct i915_gem_active *active, struct mutex *mutex) -{ - return i915_request_get(i915_gem_active_peek(active, mutex)); -} - -/** - * __i915_gem_active_get_rcu - return a reference to the active request - * @active - the active tracker - * - * __i915_gem_active_get() returns a reference to the active request, or NULL - * if the active tracker is idle. The caller must hold the RCU read lock, but - * the returned pointer is safe to use outside of RCU. - */ -static inline struct i915_request * -__i915_gem_active_get_rcu(const struct i915_gem_active *active) -{ - /* - * Performing a lockless retrieval of the active request is super - * tricky. SLAB_TYPESAFE_BY_RCU merely guarantees that the backing - * slab of request objects will not be freed whilst we hold the - * RCU read lock. It does not guarantee that the request itself - * will not be freed and then *reused*. Viz, - * - * Thread A Thread B - * - * rq = active.request - * retire(rq) -> free(rq); - * (rq is now first on the slab freelist) - * active.request = NULL - * - * rq = new submission on a new object - * ref(rq) - * - * To prevent the request from being reused whilst the caller - * uses it, we take a reference like normal. Whilst acquiring - * the reference we check that it is not in a destroyed state - * (refcnt == 0). That prevents the request being reallocated - * whilst the caller holds on to it. To check that the request - * was not reallocated as we acquired the reference we have to - * check that our request remains the active request across - * the lookup, in the same manner as a seqlock. The visibility - * of the pointer versus the reference counting is controlled - * by using RCU barriers (rcu_dereference and rcu_assign_pointer). - * - * In the middle of all that, we inspect whether the request is - * complete. Retiring is lazy so the request may be completed long - * before the active tracker is updated. Querying whether the - * request is complete is far cheaper (as it involves no locked - * instructions setting cachelines to exclusive) than acquiring - * the reference, so we do it first. The RCU read lock ensures the - * pointer dereference is valid, but does not ensure that the - * seqno nor HWS is the right one! However, if the request was - * reallocated, that means the active tracker's request was complete. - * If the new request is also complete, then both are and we can - * just report the active tracker is idle. If the new request is - * incomplete, then we acquire a reference on it and check that - * it remained the active request. - * - * It is then imperative that we do not zero the request on - * reallocation, so that we can chase the dangling pointers! - * See i915_request_alloc(). - */ - do { - struct i915_request *request; - - request = rcu_dereference(active->request); - if (!request || i915_request_completed(request)) - return NULL; - - /* - * An especially silly compiler could decide to recompute the - * result of i915_request_completed, more specifically - * re-emit the load for request->fence.seqno. A race would catch - * a later seqno value, which could flip the result from true to - * false. Which means part of the instructions below might not - * be executed, while later on instructions are executed. Due to - * barriers within the refcounting the inconsistency can't reach - * past the call to i915_request_get_rcu, but not executing - * that while still executing i915_request_put() creates - * havoc enough. Prevent this with a compiler barrier. - */ - barrier(); - - request = i915_request_get_rcu(request); - - /* - * What stops the following rcu_access_pointer() from occurring - * before the above i915_request_get_rcu()? If we were - * to read the value before pausing to get the reference to - * the request, we may not notice a change in the active - * tracker. - * - * The rcu_access_pointer() is a mere compiler barrier, which - * means both the CPU and compiler are free to perform the - * memory read without constraint. The compiler only has to - * ensure that any operations after the rcu_access_pointer() - * occur afterwards in program order. This means the read may - * be performed earlier by an out-of-order CPU, or adventurous - * compiler. - * - * The atomic operation at the heart of - * i915_request_get_rcu(), see dma_fence_get_rcu(), is - * atomic_inc_not_zero() which is only a full memory barrier - * when successful. That is, if i915_request_get_rcu() - * returns the request (and so with the reference counted - * incremented) then the following read for rcu_access_pointer() - * must occur after the atomic operation and so confirm - * that this request is the one currently being tracked. - * - * The corresponding write barrier is part of - * rcu_assign_pointer(). - */ - if (!request || request == rcu_access_pointer(active->request)) - return rcu_pointer_handoff(request); - - i915_request_put(request); - } while (1); -} - -/** - * i915_gem_active_get_unlocked - return a reference to the active request - * @active - the active tracker - * - * i915_gem_active_get_unlocked() returns a reference to the active request, - * or NULL if the active tracker is idle. The reference is obtained under RCU, - * so no locking is required by the caller. - * - * The reference should be freed with i915_request_put(). - */ -static inline struct i915_request * -i915_gem_active_get_unlocked(const struct i915_gem_active *active) -{ - struct i915_request *request; - - rcu_read_lock(); - request = __i915_gem_active_get_rcu(active); - rcu_read_unlock(); - - return request; -} - -/** - * i915_gem_active_isset - report whether the active tracker is assigned - * @active - the active tracker - * - * i915_gem_active_isset() returns true if the active tracker is currently - * assigned to a request. Due to the lazy retiring, that request may be idle - * and this may report stale information. - */ -static inline bool -i915_gem_active_isset(const struct i915_gem_active *active) -{ - return rcu_access_pointer(active->request); -} - -/** - * i915_gem_active_wait - waits until the request is completed - * @active - the active request on which to wait - * @flags - how to wait - * @timeout - how long to wait at most - * @rps - userspace client to charge for a waitboost - * - * i915_gem_active_wait() waits until the request is completed before - * returning, without requiring any locks to be held. Note that it does not - * retire any requests before returning. - * - * This function relies on RCU in order to acquire the reference to the active - * request without holding any locks. See __i915_gem_active_get_rcu() for the - * glory details on how that is managed. Once the reference is acquired, we - * can then wait upon the request, and afterwards release our reference, - * free of any locking. - * - * This function wraps i915_request_wait(), see it for the full details on - * the arguments. - * - * Returns 0 if successful, or a negative error code. - */ -static inline int -i915_gem_active_wait(const struct i915_gem_active *active, unsigned int flags) -{ - struct i915_request *request; - long ret = 0; - - request = i915_gem_active_get_unlocked(active); - if (request) { - ret = i915_request_wait(request, flags, MAX_SCHEDULE_TIMEOUT); - i915_request_put(request); - } - - return ret < 0 ? ret : 0; -} - -/** - * i915_gem_active_retire - waits until the request is retired - * @active - the active request on which to wait - * - * i915_gem_active_retire() waits until the request is completed, - * and then ensures that at least the retirement handler for this - * @active tracker is called before returning. If the @active - * tracker is idle, the function returns immediately. - */ -static inline int __must_check -i915_gem_active_retire(struct i915_gem_active *active, - struct mutex *mutex) -{ - struct i915_request *request; - long ret; - - request = i915_gem_active_raw(active, mutex); - if (!request) - return 0; - - ret = i915_request_wait(request, - I915_WAIT_INTERRUPTIBLE | I915_WAIT_LOCKED, - MAX_SCHEDULE_TIMEOUT); - if (ret < 0) - return ret; - - list_del_init(&active->link); - RCU_INIT_POINTER(active->request, NULL); - - active->retire(active, request); - - return 0; -} - -#define for_each_active(mask, idx) \ - for (; mask ? idx = ffs(mask) - 1, 1 : 0; mask &= ~BIT(idx)) - #endif /* I915_REQUEST_H */ |