linux_dsm_epyc7002/drivers/gpu/drm/i915/i915_active.h
Chris Wilson df9f85d858 drm/i915: Serialise i915_active_fence_set() with itself
The expected downside to commit 58b4c1a07a ("drm/i915: Reduce nested
prepare_remote_context() to a trylock") was that it would need to return
-EAGAIN to userspace in order to resolve potential mutex inversion. Such
an unsightly round trip is unnecessary if we could atomically insert a
barrier into the i915_active_fence, so make it happen.

Currently, we use the timeline->mutex (or some other named outer lock)
to order insertion into the i915_active_fence (and so individual nodes
of i915_active). Inside __i915_active_fence_set, we only need then
serialise with the interrupt handler in order to claim the timeline for
ourselves.

However, if we remove the outer lock, we need to ensure the order is
intact between not only multiple threads trying to insert themselves
into the timeline, but also with the interrupt handler completing the
previous occupant. We use xchg() on insert so that we have an ordered
sequence of insertions (and each caller knows the previous fence on
which to wait, preserving the chain of all fences in the timeline), but
we then have to cmpxchg() in the interrupt handler to avoid overwriting
the new occupant. The only nasty side-effect is having to temporarily
strip off the RCU-annotations to apply the atomic operations, otherwise
the rules are much more conventional!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112402
Fixes: 58b4c1a07a ("drm/i915: Reduce nested prepare_remote_context() to a trylock")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127134527.3438410-1-chris@chris-wilson.co.uk
2019-11-27 17:02:14 +00:00

208 lines
7.4 KiB
C

/*
* SPDX-License-Identifier: MIT
*
* Copyright © 2019 Intel Corporation
*/
#ifndef _I915_ACTIVE_H_
#define _I915_ACTIVE_H_
#include <linux/lockdep.h>
#include "i915_active_types.h"
#include "i915_request.h"
struct i915_request;
struct intel_engine_cs;
struct intel_timeline;
/*
* 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_active_fence to track the most recent (in
* retirement order) request relevant for the desired mode of access.
* The #i915_active_fence is updated with i915_active_fence_set() to
* track the most recent fence request, typically this is done as part of
* i915_vma_move_to_active().
*
* When the #i915_active_fence completes (is retired), it will
* signal its completion to the owner through a callback as well as mark
* itself as idle (i915_active_fence.request == NULL). The owner
* can then perform any action, such as delayed freeing of an active
* resource including itself.
*/
void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb);
/**
* __i915_active_fence_init - prepares the activity tracker for use
* @active - the active tracker
* @fence - initial fence to track, can be NULL
* @func - a callback when then the tracker is retired (becomes idle),
* can be NULL
*
* i915_active_fence_init() prepares the embedded @active struct for use as
* an activity tracker, that is for tracking the last known active fence
* associated with it. When the last fence becomes idle, when it is retired
* after completion, the optional callback @func is invoked.
*/
static inline void
__i915_active_fence_init(struct i915_active_fence *active,
void *fence,
dma_fence_func_t fn)
{
RCU_INIT_POINTER(active->fence, fence);
active->cb.func = fn ?: i915_active_noop;
}
#define INIT_ACTIVE_FENCE(A) \
__i915_active_fence_init((A), NULL, NULL)
struct dma_fence *
__i915_active_fence_set(struct i915_active_fence *active,
struct dma_fence *fence);
/**
* i915_active_fence_set - updates the tracker to watch the current fence
* @active - the active tracker
* @rq - the request to watch
*
* i915_active_fence_set() watches the given @rq for completion. While
* that @rq is busy, the @active reports busy. When that @rq is signaled
* (or else retired) the @active tracker is updated to report idle.
*/
int __must_check
i915_active_fence_set(struct i915_active_fence *active,
struct i915_request *rq);
/**
* i915_active_fence_get - return a reference to the active fence
* @active - the active tracker
*
* i915_active_fence_get() returns a reference to the active fence,
* 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 dma_fence_put().
*/
static inline struct dma_fence *
i915_active_fence_get(struct i915_active_fence *active)
{
struct dma_fence *fence;
rcu_read_lock();
fence = dma_fence_get_rcu_safe(&active->fence);
rcu_read_unlock();
return fence;
}
/**
* i915_active_fence_isset - report whether the active tracker is assigned
* @active - the active tracker
*
* i915_active_fence_isset() returns true if the active tracker is currently
* assigned to a fence. Due to the lazy retiring, that fence may be idle
* and this may report stale information.
*/
static inline bool
i915_active_fence_isset(const struct i915_active_fence *active)
{
return rcu_access_pointer(active->fence);
}
/*
* GPU activity tracking
*
* Each set of commands submitted to the GPU compromises a single request that
* signals a fence upon completion. struct i915_request combines the
* command submission, scheduling and fence signaling roles. If we want to see
* if a particular task is complete, we need to grab the fence (struct
* i915_request) for that task and check or wait for it to be signaled. More
* often though we want to track the status of a bunch of tasks, for example
* to wait for the GPU to finish accessing some memory across a variety of
* different command pipelines from different clients. We could choose to
* track every single request associated with the task, but knowing that
* each request belongs to an ordered timeline (later requests within a
* timeline must wait for earlier requests), we need only track the
* latest request in each timeline to determine the overall status of the
* task.
*
* struct i915_active provides this tracking across timelines. It builds a
* composite shared-fence, and is updated as new work is submitted to the task,
* forming a snapshot of the current status. It should be embedded into the
* different resources that need to track their associated GPU activity to
* provide a callback when that GPU activity has ceased, or otherwise to
* provide a serialisation point either for request submission or for CPU
* synchronisation.
*/
void __i915_active_init(struct i915_active *ref,
int (*active)(struct i915_active *ref),
void (*retire)(struct i915_active *ref),
struct lock_class_key *key);
#define i915_active_init(ref, active, retire) do { \
static struct lock_class_key __key; \
\
__i915_active_init(ref, active, retire, &__key); \
} while (0)
int i915_active_ref(struct i915_active *ref,
struct intel_timeline *tl,
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);
}
void i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f);
static inline bool i915_active_has_exclusive(struct i915_active *ref)
{
return rcu_access_pointer(ref->excl.fence);
}
int i915_active_wait(struct i915_active *ref);
int i915_request_await_active(struct i915_request *rq, struct i915_active *ref);
int i915_active_acquire(struct i915_active *ref);
bool i915_active_acquire_if_busy(struct i915_active *ref);
void i915_active_release(struct i915_active *ref);
static inline bool
i915_active_is_idle(const struct i915_active *ref)
{
return !atomic_read(&ref->count);
}
#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
void i915_active_fini(struct i915_active *ref);
#else
static inline void i915_active_fini(struct i915_active *ref) { }
#endif
int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
struct intel_engine_cs *engine);
void i915_active_acquire_barrier(struct i915_active *ref);
void i915_request_add_active_barriers(struct i915_request *rq);
void i915_active_print(struct i915_active *ref, struct drm_printer *m);
void i915_active_unlock_wait(struct i915_active *ref);
#endif /* _I915_ACTIVE_H_ */