Christian König
2014-May-19 12:30 UTC
[Nouveau] [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences
Am 19.05.2014 12:10, schrieb Maarten Lankhorst:> op 19-05-14 10:27, Christian K?nig schreef: >> Am 19.05.2014 10:00, schrieb Maarten Lankhorst: >> [SNIP] >> The problem here is that the whole approach collides with the way we >> do reset handling from a conceptual point of view. Every IOCTL or >> other call chain into the driver is protected by the read side of the >> exclusive_lock semaphore. So in the case of a GPU lockup we can take >> the write side of the semaphore and so make sure that we have nobody >> else accessing the hardware or internal driver structures only >> changed at init time. >> >> Leaking a drivers IRQ context into another driver as well as calling >> into a driver in atomic context is just a quite uncommon approach and >> should be considered very carefully. >> >> I would rather vote for a completely synchronous interface only >> allowing blocking waits and checks if a fence is signaled from not >> atomic context. >> >> If a driver needs to avoid blocking it should just use a workqueue >> and checking a fence outside your own driver is probably be better >> done in a bottom halve handler anyway. > > Except that you might want to do something like > fence_is_signaled() in another driver to check whether you need to > defer, or can submit the batch buffer immediately, saving a bunch of > context switches. Running the is_signaled atomic is really useful here > because it means you can't do too many scary things in your is_signaled > handler.This is indeed a nice optimization, but nothing more. If you want to provide a is_signalled interface for atomic context then this should be optional, not mandatory.> > In case of enable_signaling it was the only sane solution, because > fence_signal can be called from irq context, and any calls after that to > fence_add_callback and fence_wait aren't allowed to do anything, so > fence_enable_sw_signaling and the default wait implementation must be > atomic. fence_wait itself doesn't have to be, so it's easy to grab > exclusive_lock there.I don't think you understood my point here: Completely drop enable_signaling, it's unnecessary and only complicates the interface. We purposely avoided exactly this paradigm in the past and I haven't seen any good argument to start with it now. Christian.> > Simple fence drivers may drop some state after calling fence_signal, so > calling .enable_signaling after fence_signal is bad, and fence_signal > must also wait for any previous call to enable_signaling to be > completed. This means those functions have to be implemented with the > atomic spinlock held and irqs disabled. :-) The .signaled callback could > strictly speaking still be called after fence_signal is called, but > this function is optional. > > I tried other locking approaches, but when I used a separate spinlock > for the fence things got even messier and I ended up with impossible to > eliminate locking inversions, or I removed the guarantee that calling > fence_signal meant that enable_signaling had either been not called or > completed, or other bugs and much harder to read code. > > ~Maarten > > Revised diff below. > --- > diff --git a/drivers/gpu/drm/radeon/radeon.h > b/drivers/gpu/drm/radeon/radeon.h > index 68528619834a..a7d839a158ae 100644 > --- a/drivers/gpu/drm/radeon/radeon.h > +++ b/drivers/gpu/drm/radeon/radeon.h > @@ -64,6 +64,7 @@ > #include <linux/wait.h> > #include <linux/list.h> > #include <linux/kref.h> > +#include <linux/fence.h> > > #include <ttm/ttm_bo_api.h> > #include <ttm/ttm_bo_driver.h> > @@ -113,9 +114,6 @@ extern int radeon_hard_reset; > #define RADEONFB_CONN_LIMIT 4 > #define RADEON_BIOS_NUM_SCRATCH 8 > > -/* fence seq are set to this number when signaled */ > -#define RADEON_FENCE_SIGNALED_SEQ 0LL > - > /* internal ring indices */ > /* r1xx+ has gfx CP ring */ > #define RADEON_RING_TYPE_GFX_INDEX 0 > @@ -347,12 +345,15 @@ struct radeon_fence_driver { > }; > > struct radeon_fence { > + struct fence base; > + > struct radeon_device *rdev; > - struct kref kref; > /* protected by radeon_fence.lock */ > uint64_t seq; > /* RB, DMA, etc. */ > unsigned ring; > + > + wait_queue_t fence_wake; > }; > > int radeon_fence_driver_start_ring(struct radeon_device *rdev, int > ring); > @@ -2256,6 +2257,7 @@ struct radeon_device { > struct radeon_mman mman; > struct radeon_fence_driver fence_drv[RADEON_NUM_RINGS]; > wait_queue_head_t fence_queue; > + unsigned fence_context; > struct mutex ring_lock; > struct radeon_ring ring[RADEON_NUM_RINGS]; > bool ib_pool_ready; > @@ -2346,11 +2348,6 @@ u32 cik_mm_rdoorbell(struct radeon_device > *rdev, u32 index); > void cik_mm_wdoorbell(struct radeon_device *rdev, u32 index, u32 v); > > /* > - * Cast helper > - */ > -#define to_radeon_fence(p) ((struct radeon_fence *)(p)) > - > -/* > * Registers read & write functions. > */ > #define RREG8(reg) readb((rdev->rmmio) + (reg)) > diff --git a/drivers/gpu/drm/radeon/radeon_device.c > b/drivers/gpu/drm/radeon/radeon_device.c > index 0e770bbf7e29..19c6911ed49f 100644 > --- a/drivers/gpu/drm/radeon/radeon_device.c > +++ b/drivers/gpu/drm/radeon/radeon_device.c > @@ -1175,6 +1175,7 @@ int radeon_device_init(struct radeon_device *rdev, > for (i = 0; i < RADEON_NUM_RINGS; i++) { > rdev->ring[i].idx = i; > } > + rdev->fence_context = fence_context_alloc(RADEON_NUM_RINGS); > > DRM_INFO("initializing kernel modesetting (%s 0x%04X:0x%04X > 0x%04X:0x%04X).\n", > radeon_family_name[rdev->family], pdev->vendor, pdev->device, > @@ -1565,6 +1566,54 @@ int radeon_resume_kms(struct drm_device *dev, > bool resume, bool fbcon) > return 0; > } > > +static uint32_t radeon_gpu_mask_sw_irq(struct radeon_device *rdev) > +{ > + uint32_t mask = 0; > + int i; > + > + if (!rdev->ddev->irq_enabled) > + return mask; > + > + /* > + * increase refcount on sw interrupts for all rings to stop > + * enabling interrupts in radeon_fence_enable_signaling during > + * gpu reset. > + */ > + > + for (i = 0; i < RADEON_NUM_RINGS; ++i) { > + if (!rdev->ring[i].ready) > + continue; > + > + atomic_inc(&rdev->irq.ring_int[i]); > + mask |= 1 << i; > + } > + return mask; > +} > + > +static void radeon_gpu_unmask_sw_irq(struct radeon_device *rdev, > uint32_t mask) > +{ > + unsigned long irqflags; > + int i; > + > + if (!mask) > + return; > + > + /* > + * undo refcount increase, and reset irqs to correct value. > + */ > + > + for (i = 0; i < RADEON_NUM_RINGS; ++i) { > + if (!(mask & (1 << i))) > + continue; > + > + atomic_dec(&rdev->irq.ring_int[i]); > + } > + > + spin_lock_irqsave(&rdev->irq.lock, irqflags); > + radeon_irq_set(rdev); > + spin_unlock_irqrestore(&rdev->irq.lock, irqflags); > +} > + > /** > * radeon_gpu_reset - reset the asic > * > @@ -1582,6 +1631,7 @@ int radeon_gpu_reset(struct radeon_device *rdev) > > int i, r; > int resched; > + uint32_t sw_mask; > > down_write(&rdev->exclusive_lock); > > @@ -1595,6 +1645,7 @@ int radeon_gpu_reset(struct radeon_device *rdev) > radeon_save_bios_scratch_regs(rdev); > /* block TTM */ > resched = ttm_bo_lock_delayed_workqueue(&rdev->mman.bdev); > + sw_mask = radeon_gpu_mask_sw_irq(rdev); > radeon_pm_suspend(rdev); > radeon_suspend(rdev); > > @@ -1644,6 +1695,7 @@ retry: > radeon_pm_resume(rdev); > drm_helper_resume_force_mode(rdev->ddev); > > + radeon_gpu_unmask_sw_irq(rdev, sw_mask); > ttm_bo_unlock_delayed_workqueue(&rdev->mman.bdev, resched); > if (r) { > /* bad news, how to tell it to userspace ? */ > diff --git a/drivers/gpu/drm/radeon/radeon_fence.c > b/drivers/gpu/drm/radeon/radeon_fence.c > index a77b1c13ea43..db1f3b4708fa 100644 > --- a/drivers/gpu/drm/radeon/radeon_fence.c > +++ b/drivers/gpu/drm/radeon/radeon_fence.c > @@ -39,6 +39,15 @@ > #include "radeon.h" > #include "radeon_trace.h" > > +static const struct fence_ops radeon_fence_ops; > + > +#define to_radeon_fence(p) \ > + ({ \ > + struct radeon_fence *__f; \ > + __f = container_of((p), struct radeon_fence, base); \ > + __f->base.ops == &radeon_fence_ops ? __f : NULL; \ > + }) > + > /* > * Fences > * Fences mark an event in the GPUs pipeline and are used > @@ -111,30 +120,55 @@ int radeon_fence_emit(struct radeon_device *rdev, > struct radeon_fence **fence, > int ring) > { > + u64 seq = ++rdev->fence_drv[ring].sync_seq[ring]; > + > /* we are protected by the ring emission mutex */ > *fence = kmalloc(sizeof(struct radeon_fence), GFP_KERNEL); > if ((*fence) == NULL) { > return -ENOMEM; > } > - kref_init(&((*fence)->kref)); > - (*fence)->rdev = rdev; > - (*fence)->seq = ++rdev->fence_drv[ring].sync_seq[ring]; > (*fence)->ring = ring; > + __fence_init(&(*fence)->base, &radeon_fence_ops, > + &rdev->fence_queue.lock, rdev->fence_context + ring, seq); > + (*fence)->rdev = rdev; > + (*fence)->seq = seq; > radeon_fence_ring_emit(rdev, ring, *fence); > trace_radeon_fence_emit(rdev->ddev, ring, (*fence)->seq); > return 0; > } > > /** > - * radeon_fence_process - process a fence > - * > - * @rdev: radeon_device pointer > - * @ring: ring index the fence is associated with > + * radeon_fence_check_signaled - callback from fence_queue > * > - * Checks the current fence value and wakes the fence queue > - * if the sequence number has increased (all asics). > + * this function is called with fence_queue lock held, which is also > used > + * for the fence locking itself, so unlocked variants are used for > + * fence_signal, and remove_wait_queue. > */ > -void radeon_fence_process(struct radeon_device *rdev, int ring) > +static int radeon_fence_check_signaled(wait_queue_t *wait, unsigned > mode, int flags, void *key) > +{ > + struct radeon_fence *fence; > + u64 seq; > + > + fence = container_of(wait, struct radeon_fence, fence_wake); > + > + seq = atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq); > + if (seq >= fence->seq) { > + int ret = __fence_signal(&fence->base); > + > + if (!ret) > + FENCE_TRACE(&fence->base, "signaled from irq context\n"); > + else > + FENCE_TRACE(&fence->base, "was already signaled\n"); > + > + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring); > + __remove_wait_queue(&fence->rdev->fence_queue, > &fence->fence_wake); > + fence_put(&fence->base); > + } else > + FENCE_TRACE(&fence->base, "pending\n"); > + return 0; > +} > + > +static bool __radeon_fence_process(struct radeon_device *rdev, int ring) > { > uint64_t seq, last_seq, last_emitted; > unsigned count_loop = 0; > @@ -190,23 +224,22 @@ void radeon_fence_process(struct radeon_device > *rdev, int ring) > } > } while (atomic64_xchg(&rdev->fence_drv[ring].last_seq, seq) > seq); > > - if (wake) > - wake_up_all(&rdev->fence_queue); > + return wake; > } > > /** > - * radeon_fence_destroy - destroy a fence > + * radeon_fence_process - process a fence > * > - * @kref: fence kref > + * @rdev: radeon_device pointer > + * @ring: ring index the fence is associated with > * > - * Frees the fence object (all asics). > + * Checks the current fence value and wakes the fence queue > + * if the sequence number has increased (all asics). > */ > -static void radeon_fence_destroy(struct kref *kref) > +void radeon_fence_process(struct radeon_device *rdev, int ring) > { > - struct radeon_fence *fence; > - > - fence = container_of(kref, struct radeon_fence, kref); > - kfree(fence); > + if (__radeon_fence_process(rdev, ring)) > + wake_up_all(&rdev->fence_queue); > } > > /** > @@ -237,6 +270,69 @@ static bool radeon_fence_seq_signaled(struct > radeon_device *rdev, > return false; > } > > +static bool __radeon_fence_signaled(struct fence *f) > +{ > + struct radeon_fence *fence = to_radeon_fence(f); > + struct radeon_device *rdev = fence->rdev; > + unsigned ring = fence->ring; > + u64 seq = fence->seq; > + > + if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq) { > + return true; > + } > + > + if (down_read_trylock(&rdev->exclusive_lock)) { > + radeon_fence_process(rdev, ring); > + up_read(&rdev->exclusive_lock); > + > + if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq) { > + return true; > + } > + } > + return false; > +} > + > +/** > + * radeon_fence_enable_signaling - enable signalling on fence > + * @fence: fence > + * > + * This function is called with fence_queue lock held, and adds a > callback > + * to fence_queue that checks if this fence is signaled, and if so it > + * signals the fence and removes itself. > + */ > +static bool radeon_fence_enable_signaling(struct fence *f) > +{ > + struct radeon_fence *fence = to_radeon_fence(f); > + struct radeon_device *rdev = fence->rdev; > + > + if (atomic64_read(&rdev->fence_drv[fence->ring].last_seq) >= > fence->seq || > + !rdev->ddev->irq_enabled) > + return false; > + > + radeon_irq_kms_sw_irq_get(rdev, fence->ring); > + > + if (down_read_trylock(&rdev->exclusive_lock)) { > + if (__radeon_fence_process(rdev, fence->ring)) > + wake_up_all_locked(&rdev->fence_queue); > + > + up_read(&rdev->exclusive_lock); > + } > + > + /* did fence get signaled after we enabled the sw irq? */ > + if (atomic64_read(&rdev->fence_drv[fence->ring].last_seq) >= > fence->seq) { > + radeon_irq_kms_sw_irq_put(rdev, fence->ring); > + return false; > + } > + > + fence->fence_wake.flags = 0; > + fence->fence_wake.private = NULL; > + fence->fence_wake.func = radeon_fence_check_signaled; > + __add_wait_queue(&rdev->fence_queue, &fence->fence_wake); > + fence_get(f); > + > + return true; > +} > + > /** > * radeon_fence_signaled - check if a fence has signaled > * > @@ -250,11 +346,13 @@ bool radeon_fence_signaled(struct radeon_fence > *fence) > if (!fence) { > return true; > } > - if (fence->seq == RADEON_FENCE_SIGNALED_SEQ) { > - return true; > - } > + > if (radeon_fence_seq_signaled(fence->rdev, fence->seq, > fence->ring)) { > - fence->seq = RADEON_FENCE_SIGNALED_SEQ; > + int ret; > + > + ret = fence_signal(&fence->base); > + if (!ret) > + FENCE_TRACE(&fence->base, "signaled from > radeon_fence_signaled\n"); > return true; > } > return false; > @@ -283,28 +381,35 @@ static bool radeon_fence_any_seq_signaled(struct > radeon_device *rdev, u64 *seq) > } > > /** > - * radeon_fence_wait_seq - wait for a specific sequence numbers > + * radeon_fence_wait_seq_timeout - wait for a specific sequence numbers > * > * @rdev: radeon device pointer > * @target_seq: sequence number(s) we want to wait for > * @intr: use interruptable sleep > + * @timeout: maximum time to wait, or MAX_SCHEDULE_TIMEOUT for > infinite wait > * > * Wait for the requested sequence number(s) to be written by any ring > * (all asics). Sequnce number array is indexed by ring id. > * @intr selects whether to use interruptable (true) or > non-interruptable > * (false) sleep when waiting for the sequence number. Helper function > * for radeon_fence_wait_*(). > - * Returns 0 if the sequence number has passed, error for all other > cases. > + * Returns remaining time if the sequence number has passed, 0 when > + * the wait timeout, or an error for all other cases. > * -EDEADLK is returned when a GPU lockup has been detected. > */ > -static int radeon_fence_wait_seq(struct radeon_device *rdev, u64 > *target_seq, > - bool intr) > +static int radeon_fence_wait_seq_timeout(struct radeon_device *rdev, > + u64 *target_seq, bool intr, > + long timeout) > { > uint64_t last_seq[RADEON_NUM_RINGS]; > bool signaled; > - int i, r; > + int i; > > while (!radeon_fence_any_seq_signaled(rdev, target_seq)) { > + long r, waited = timeout; > + > + waited = timeout < RADEON_FENCE_JIFFIES_TIMEOUT ? > + timeout : RADEON_FENCE_JIFFIES_TIMEOUT; > > /* Save current sequence values, used to check for GPU > lockups */ > for (i = 0; i < RADEON_NUM_RINGS; ++i) { > @@ -319,13 +424,15 @@ static int radeon_fence_wait_seq(struct > radeon_device *rdev, u64 *target_seq, > if (intr) { > r = wait_event_interruptible_timeout(rdev->fence_queue, ( > (signaled = radeon_fence_any_seq_signaled(rdev, > target_seq)) > - || rdev->needs_reset), RADEON_FENCE_JIFFIES_TIMEOUT); > + || rdev->needs_reset), waited); > } else { > r = wait_event_timeout(rdev->fence_queue, ( > (signaled = radeon_fence_any_seq_signaled(rdev, > target_seq)) > - || rdev->needs_reset), RADEON_FENCE_JIFFIES_TIMEOUT); > + || rdev->needs_reset), waited); > } > > + timeout -= waited - r; > + > for (i = 0; i < RADEON_NUM_RINGS; ++i) { > if (!target_seq[i]) > continue; > @@ -337,6 +444,12 @@ static int radeon_fence_wait_seq(struct > radeon_device *rdev, u64 *target_seq, > if (unlikely(r < 0)) > return r; > > + /* > + * If this is a timed wait and the wait completely timed out > just return. > + */ > + if (!timeout) > + break; > + > if (unlikely(!signaled)) { > if (rdev->needs_reset) > return -EDEADLK; > @@ -379,14 +492,14 @@ static int radeon_fence_wait_seq(struct > radeon_device *rdev, u64 *target_seq, > } > } > } > - return 0; > + return timeout; > } > > /** > * radeon_fence_wait - wait for a fence to signal > * > * @fence: radeon fence object > - * @intr: use interruptable sleep > + * @intr: use interruptible sleep > * > * Wait for the requested fence to signal (all asics). > * @intr selects whether to use interruptable (true) or > non-interruptable > @@ -398,20 +511,17 @@ int radeon_fence_wait(struct radeon_fence > *fence, bool intr) > uint64_t seq[RADEON_NUM_RINGS] = {}; > int r; > > - if (fence == NULL) { > - WARN(1, "Querying an invalid fence : %p !\n", fence); > - return -EINVAL; > - } > - > - seq[fence->ring] = fence->seq; > - if (seq[fence->ring] == RADEON_FENCE_SIGNALED_SEQ) > + if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->base.flags)) > return 0; > > - r = radeon_fence_wait_seq(fence->rdev, seq, intr); > - if (r) > + seq[fence->ring] = fence->seq; > + r = radeon_fence_wait_seq_timeout(fence->rdev, seq, intr, > MAX_SCHEDULE_TIMEOUT); > + if (r < 0) { > return r; > - > - fence->seq = RADEON_FENCE_SIGNALED_SEQ; > + } > + r = fence_signal(&fence->base); > + if (!r) > + FENCE_TRACE(&fence->base, "signaled from fence_wait\n"); > return 0; > } > > @@ -434,7 +544,7 @@ int radeon_fence_wait_any(struct radeon_device *rdev, > { > uint64_t seq[RADEON_NUM_RINGS]; > unsigned i, num_rings = 0; > - int r; > + long r; > > for (i = 0; i < RADEON_NUM_RINGS; ++i) { > seq[i] = 0; > @@ -443,20 +553,21 @@ int radeon_fence_wait_any(struct radeon_device > *rdev, > continue; > } > > + if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fences[i]->base.flags)) { > + /* already signaled */ > + return 0; > + } > + > seq[i] = fences[i]->seq; > ++num_rings; > - > - /* test if something was allready signaled */ > - if (seq[i] == RADEON_FENCE_SIGNALED_SEQ) > - return 0; > } > > /* nothing to wait for ? */ > if (num_rings == 0) > return -ENOENT; > > - r = radeon_fence_wait_seq(rdev, seq, intr); > - if (r) { > + r = radeon_fence_wait_seq_timeout(rdev, seq, intr, > MAX_SCHEDULE_TIMEOUT); > + if (r < 0) { > return r; > } > return 0; > @@ -475,6 +586,7 @@ int radeon_fence_wait_any(struct radeon_device *rdev, > int radeon_fence_wait_next(struct radeon_device *rdev, int ring) > { > uint64_t seq[RADEON_NUM_RINGS] = {}; > + long r; > > seq[ring] = atomic64_read(&rdev->fence_drv[ring].last_seq) + 1ULL; > if (seq[ring] >= rdev->fence_drv[ring].sync_seq[ring]) { > @@ -482,7 +594,10 @@ int radeon_fence_wait_next(struct radeon_device > *rdev, int ring) > already the last emited fence */ > return -ENOENT; > } > - return radeon_fence_wait_seq(rdev, seq, false); > + r = radeon_fence_wait_seq_timeout(rdev, seq, false, > MAX_SCHEDULE_TIMEOUT); > + if (r < 0) > + return r; > + return 0; > } > > /** > @@ -504,8 +619,8 @@ int radeon_fence_wait_empty(struct radeon_device > *rdev, int ring) > if (!seq[ring]) > return 0; > > - r = radeon_fence_wait_seq(rdev, seq, false); > - if (r) { > + r = radeon_fence_wait_seq_timeout(rdev, seq, false, > MAX_SCHEDULE_TIMEOUT); > + if (r < 0) { > if (r == -EDEADLK) > return -EDEADLK; > > @@ -525,7 +640,7 @@ int radeon_fence_wait_empty(struct radeon_device > *rdev, int ring) > */ > struct radeon_fence *radeon_fence_ref(struct radeon_fence *fence) > { > - kref_get(&fence->kref); > + fence_get(&fence->base); > return fence; > } > > @@ -541,9 +656,8 @@ void radeon_fence_unref(struct radeon_fence **fence) > struct radeon_fence *tmp = *fence; > > *fence = NULL; > - if (tmp) { > - kref_put(&tmp->kref, radeon_fence_destroy); > - } > + if (tmp) > + fence_put(&tmp->base); > } > > /** > @@ -832,3 +946,51 @@ int radeon_debugfs_fence_init(struct > radeon_device *rdev) > return 0; > #endif > } > + > +static long __radeon_fence_wait(struct fence *f, bool intr, long > timeout) > +{ > + struct radeon_fence *fence = to_radeon_fence(f); > + u64 target_seq[RADEON_NUM_RINGS] = {}; > + struct radeon_device *rdev = fence->rdev; > + unsigned long r; > + > + target_seq[fence->ring] = fence->seq; > + > + down_read(&rdev->exclusive_lock); > + r = radeon_fence_wait_seq_timeout(fence->rdev, target_seq, intr, > timeout); > + > + if (r > 0 && !fence_signal(&fence->base)) > + FENCE_TRACE(&fence->base, "signaled from > __radeon_fence_wait\n"); > + > + up_read(&rdev->exclusive_lock); > + return r; > + > +} > + > +static const char *radeon_fence_get_driver_name(struct fence *fence) > +{ > + return "radeon"; > +} > + > +static const char *radeon_fence_get_timeline_name(struct fence *f) > +{ > + struct radeon_fence *fence = to_radeon_fence(f); > + switch (fence->ring) { > + case RADEON_RING_TYPE_GFX_INDEX: return "radeon.gfx"; > + case CAYMAN_RING_TYPE_CP1_INDEX: return "radeon.cp1"; > + case CAYMAN_RING_TYPE_CP2_INDEX: return "radeon.cp2"; > + case R600_RING_TYPE_DMA_INDEX: return "radeon.dma"; > + case CAYMAN_RING_TYPE_DMA1_INDEX: return "radeon.dma1"; > + case R600_RING_TYPE_UVD_INDEX: return "radeon.uvd"; > + default: WARN_ON_ONCE(1); return "radeon.unk"; > + } > +} > + > +static const struct fence_ops radeon_fence_ops = { > + .get_driver_name = radeon_fence_get_driver_name, > + .get_timeline_name = radeon_fence_get_timeline_name, > + .enable_signaling = radeon_fence_enable_signaling, > + .signaled = __radeon_fence_signaled, > + .wait = __radeon_fence_wait, > + .release = NULL, > +}; > > > ---- >
Maarten Lankhorst
2014-May-19 13:35 UTC
[Nouveau] [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences
op 19-05-14 14:30, Christian K?nig schreef:> Am 19.05.2014 12:10, schrieb Maarten Lankhorst: >> op 19-05-14 10:27, Christian K?nig schreef: >>> Am 19.05.2014 10:00, schrieb Maarten Lankhorst: >>> [SNIP] >>> The problem here is that the whole approach collides with the way we do reset handling from a conceptual point of view. Every IOCTL or other call chain into the driver is protected by the read side of the exclusive_lock semaphore. So in the case of a GPU lockup we can take the write side of the semaphore and so make sure that we have nobody else accessing the hardware or internal driver structures only changed at init time. >>> >>> Leaking a drivers IRQ context into another driver as well as calling into a driver in atomic context is just a quite uncommon approach and should be considered very carefully. >>> >>> I would rather vote for a completely synchronous interface only allowing blocking waits and checks if a fence is signaled from not atomic context. >>> >>> If a driver needs to avoid blocking it should just use a workqueue and checking a fence outside your own driver is probably be better done in a bottom halve handler anyway. >> >> Except that you might want to do something like >> fence_is_signaled() in another driver to check whether you need to >> defer, or can submit the batch buffer immediately, saving a bunch of >> context switches. Running the is_signaled atomic is really useful here >> because it means you can't do too many scary things in your is_signaled >> handler. > > This is indeed a nice optimization, but nothing more. If you want to provide a is_signalled interface for atomic context then this should be optional, not mandatory.See below.>> In case of enable_signaling it was the only sane solution, because >> fence_signal can be called from irq context, and any calls after that to >> fence_add_callback and fence_wait aren't allowed to do anything, so >> fence_enable_sw_signaling and the default wait implementation must be >> atomic. fence_wait itself doesn't have to be, so it's easy to grab >> exclusive_lock there. > > I don't think you understood my point here: Completely drop enable_signaling, it's unnecessary and only complicates the interface. > > We purposely avoided exactly this paradigm in the past and I haven't seen any good argument to start with it now.In the common case a lot more fences will be emitted than will be waited on. This means it makes sense to delay signaling a fence with fence_signal for as long as possible. But when a fence user wants to work with a fence some way is needed to ensure that the fence will complete. This is the idea behind .enable_signaling, it tells the fence driver to call fence_signal on the fence 'soon' because there are now waiters for it. The atomic .signaled is optional, and can be set to NULL, but there is no guarantee that fence_is_signaled will ever return true in that case, unless fence_enable_sw_signaling is called (which calls .enable_signaling). Providing a custom wait function is optional in the interface, if the default wait function is used all waiters are signaled when fence_signal is called. Removing enable_signaling would only make sense if fence_signal was removed too, but that would mean that fence_is_signaled could no longer exist in the core fence code, and would mean completely rewriting the interface. ~Maarten
Christian König
2014-May-19 14:25 UTC
[Nouveau] [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences
Am 19.05.2014 15:35, schrieb Maarten Lankhorst:> op 19-05-14 14:30, Christian K?nig schreef: >> Am 19.05.2014 12:10, schrieb Maarten Lankhorst: >>> op 19-05-14 10:27, Christian K?nig schreef: >>>> Am 19.05.2014 10:00, schrieb Maarten Lankhorst: >>>> [SNIP] >>>> The problem here is that the whole approach collides with the way >>>> we do reset handling from a conceptual point of view. Every IOCTL >>>> or other call chain into the driver is protected by the read side >>>> of the exclusive_lock semaphore. So in the case of a GPU lockup we >>>> can take the write side of the semaphore and so make sure that we >>>> have nobody else accessing the hardware or internal driver >>>> structures only changed at init time. >>>> >>>> Leaking a drivers IRQ context into another driver as well as >>>> calling into a driver in atomic context is just a quite uncommon >>>> approach and should be considered very carefully. >>>> >>>> I would rather vote for a completely synchronous interface only >>>> allowing blocking waits and checks if a fence is signaled from not >>>> atomic context. >>>> >>>> If a driver needs to avoid blocking it should just use a workqueue >>>> and checking a fence outside your own driver is probably be better >>>> done in a bottom halve handler anyway. >>> >>> Except that you might want to do something like >>> fence_is_signaled() in another driver to check whether you need to >>> defer, or can submit the batch buffer immediately, saving a bunch of >>> context switches. Running the is_signaled atomic is really useful here >>> because it means you can't do too many scary things in your is_signaled >>> handler. >> >> This is indeed a nice optimization, but nothing more. If you want to >> provide a is_signalled interface for atomic context then this should >> be optional, not mandatory. > See below. >>> In case of enable_signaling it was the only sane solution, because >>> fence_signal can be called from irq context, and any calls after >>> that to >>> fence_add_callback and fence_wait aren't allowed to do anything, so >>> fence_enable_sw_signaling and the default wait implementation must be >>> atomic. fence_wait itself doesn't have to be, so it's easy to grab >>> exclusive_lock there. >> >> I don't think you understood my point here: Completely drop >> enable_signaling, it's unnecessary and only complicates the interface. >> >> We purposely avoided exactly this paradigm in the past and I haven't >> seen any good argument to start with it now. > > In the common case a lot more fences will be emitted than will be > waited on. > This means it makes sense to delay signaling a fence with fence_signal > for > as long as possible. But when a fence user wants to work with a fence > some way is needed to ensure that the fence will complete. This is the > idea > behind .enable_signaling, it tells the fence driver to call > fence_signal on > the fence 'soon' because there are now waiters for it. > > The atomic .signaled is optional, and can be set to NULL, but there is > no guarantee that fence_is_signaled will ever return true in that case, > unless fence_enable_sw_signaling is called (which calls > .enable_signaling). > > Providing a custom wait function is optional in the interface, if the > default wait > function is used all waiters are signaled when fence_signal is called. > > Removing enable_signaling would only make sense if fence_signal was > removed too, > but that would mean that fence_is_signaled could no longer exist in > the core fence > code, and would mean completely rewriting the interface. >And this is what I'm suggesting here. We have avoided quite hard adding any form of those callbacks in the past and I don't really see a reason why that would have changed. For example see the discussion here: http://lists.freedesktop.org/archives/dri-devel/2012-May/022388.html Jerome and Dave rejected my approach for handling the sub allocator through a callback for exactly the same reason. And that was even for call chains inside the same driver, you're suggesting this for cross driver synchronization. Christian.
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