Re: [PATCH 05/13] drm/i915: Convert requests to use struct fence

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On 12/17/2015 09:43 AM, Jesse Barnes wrote:
> On 12/11/2015 05:11 AM, John.C.Harrison@xxxxxxxxx wrote:
>> From: John Harrison <John.C.Harrison@xxxxxxxxx>
>>
>> There is a construct in the linux kernel called 'struct fence' that is
>> intended to keep track of work that is executed on hardware. I.e. it
>> solves the basic problem that the drivers 'struct
>> drm_i915_gem_request' is trying to address. The request structure does
>> quite a lot more than simply track the execution progress so is very
>> definitely still required. However, the basic completion status side
>> could be updated to use the ready made fence implementation and gain
>> all the advantages that provides.
>>
>> This patch makes the first step of integrating a struct fence into the
>> request. It replaces the explicit reference count with that of the
>> fence. It also replaces the 'is completed' test with the fence's
>> equivalent. Currently, that simply chains on to the original request
>> implementation. A future patch will improve this.
>>
>> v3: Updated after review comments by Tvrtko Ursulin. Added fence
>> context/seqno pair to the debugfs request info. Renamed fence 'driver
>> name' to just 'i915'. Removed BUG_ONs.
>>
>> For: VIZ-5190
>> Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
>> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>> ---
>>  drivers/gpu/drm/i915/i915_debugfs.c     |  5 +--
>>  drivers/gpu/drm/i915/i915_drv.h         | 45 +++++++++++++-------------
>>  drivers/gpu/drm/i915/i915_gem.c         | 56 ++++++++++++++++++++++++++++++---
>>  drivers/gpu/drm/i915/intel_lrc.c        |  1 +
>>  drivers/gpu/drm/i915/intel_ringbuffer.c |  1 +
>>  drivers/gpu/drm/i915/intel_ringbuffer.h |  3 ++
>>  6 files changed, 81 insertions(+), 30 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
>> index 7415606..5b31186 100644
>> --- a/drivers/gpu/drm/i915/i915_debugfs.c
>> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
>> @@ -709,11 +709,12 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
>>  			task = NULL;
>>  			if (req->pid)
>>  				task = pid_task(req->pid, PIDTYPE_PID);
>> -			seq_printf(m, "    %x @ %d: %s [%d]\n",
>> +			seq_printf(m, "    %x @ %d: %s [%d], fence = %u.%u\n",
>>  				   req->seqno,
>>  				   (int) (jiffies - req->emitted_jiffies),
>>  				   task ? task->comm : "<unknown>",
>> -				   task ? task->pid : -1);
>> +				   task ? task->pid : -1,
>> +				   req->fence.context, req->fence.seqno);
>>  			rcu_read_unlock();
>>  		}
>>  
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> index 436149e..aa5cba7 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -51,6 +51,7 @@
>>  #include <linux/kref.h>
>>  #include <linux/pm_qos.h>
>>  #include "intel_guc.h"
>> +#include <linux/fence.h>
>>  
>>  /* General customization:
>>   */
>> @@ -2174,7 +2175,17 @@ void i915_gem_track_fb(struct drm_i915_gem_object *old,
>>   * initial reference taken using kref_init
>>   */
>>  struct drm_i915_gem_request {
>> -	struct kref ref;
>> +	/**
>> +	 * Underlying object for implementing the signal/wait stuff.
>> +	 * NB: Never call fence_later() or return this fence object to user
>> +	 * land! Due to lazy allocation, scheduler re-ordering, pre-emption,
>> +	 * etc., there is no guarantee at all about the validity or
>> +	 * sequentiality of the fence's seqno! It is also unsafe to let
>> +	 * anything outside of the i915 driver get hold of the fence object
>> +	 * as the clean up when decrementing the reference count requires
>> +	 * holding the driver mutex lock.
>> +	 */
>> +	struct fence fence;
>>  
>>  	/** On Which ring this request was generated */
>>  	struct drm_i915_private *i915;
>> @@ -2251,7 +2262,13 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>>  			   struct intel_context *ctx,
>>  			   struct drm_i915_gem_request **req_out);
>>  void i915_gem_request_cancel(struct drm_i915_gem_request *req);
>> -void i915_gem_request_free(struct kref *req_ref);
>> +
>> +static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
>> +					      bool lazy_coherency)
>> +{
>> +	return fence_is_signaled(&req->fence);
>> +}
>> +
>>  int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
>>  				   struct drm_file *file);
>>  
>> @@ -2271,7 +2288,7 @@ static inline struct drm_i915_gem_request *
>>  i915_gem_request_reference(struct drm_i915_gem_request *req)
>>  {
>>  	if (req)
>> -		kref_get(&req->ref);
>> +		fence_get(&req->fence);
>>  	return req;
>>  }
>>  
>> @@ -2279,7 +2296,7 @@ static inline void
>>  i915_gem_request_unreference(struct drm_i915_gem_request *req)
>>  {
>>  	WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
>> -	kref_put(&req->ref, i915_gem_request_free);
>> +	fence_put(&req->fence);
>>  }
>>  
>>  static inline void
>> @@ -2291,7 +2308,7 @@ i915_gem_request_unreference__unlocked(struct drm_i915_gem_request *req)
>>  		return;
>>  
>>  	dev = req->ring->dev;
>> -	if (kref_put_mutex(&req->ref, i915_gem_request_free, &dev->struct_mutex))
>> +	if (kref_put_mutex(&req->fence.refcount, fence_release, &dev->struct_mutex))
>>  		mutex_unlock(&dev->struct_mutex);
>>  }
>>  
>> @@ -2308,12 +2325,6 @@ static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
>>  }
>>  
>>  /*
>> - * XXX: i915_gem_request_completed should be here but currently needs the
>> - * definition of i915_seqno_passed() which is below. It will be moved in
>> - * a later patch when the call to i915_seqno_passed() is obsoleted...
>> - */
>> -
>> -/*
>>   * A command that requires special handling by the command parser.
>>   */
>>  struct drm_i915_cmd_descriptor {
>> @@ -2916,18 +2927,6 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
>>  	return (int32_t)(seq1 - seq2) >= 0;
>>  }
>>  
>> -static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
>> -					      bool lazy_coherency)
>> -{
>> -	u32 seqno;
>> -
>> -	BUG_ON(req == NULL);
>> -
>> -	seqno = req->ring->get_seqno(req->ring, lazy_coherency);
>> -
>> -	return i915_seqno_passed(seqno, req->seqno);
>> -}
>> -
>>  int __must_check i915_gem_get_seqno(struct drm_device *dev, u32 *seqno);
>>  int __must_check i915_gem_set_seqno(struct drm_device *dev, u32 seqno);
>>  
>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>> index e4056a3..a1b4dbd 100644
>> --- a/drivers/gpu/drm/i915/i915_gem.c
>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>> @@ -2617,12 +2617,14 @@ static void i915_set_reset_status(struct drm_i915_private *dev_priv,
>>  	}
>>  }
>>  
>> -void i915_gem_request_free(struct kref *req_ref)
>> +static void i915_gem_request_free(struct fence *req_fence)
>>  {
>> -	struct drm_i915_gem_request *req = container_of(req_ref,
>> -						 typeof(*req), ref);
>> +	struct drm_i915_gem_request *req = container_of(req_fence,
>> +						 typeof(*req), fence);
>>  	struct intel_context *ctx = req->ctx;
>>  
>> +	WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
>> +
>>  	if (req->file_priv)
>>  		i915_gem_request_remove_from_client(req);
>>  
>> @@ -2638,6 +2640,45 @@ void i915_gem_request_free(struct kref *req_ref)
>>  	kmem_cache_free(req->i915->requests, req);
>>  }
>>  
>> +static bool i915_gem_request_enable_signaling(struct fence *req_fence)
>> +{
>> +	/* Interrupt driven fences are not implemented yet.*/
>> +	WARN(true, "This should not be called!");
>> +	return true;
>> +}
>> +
>> +static bool i915_gem_request_is_completed(struct fence *req_fence)
>> +{
>> +	struct drm_i915_gem_request *req = container_of(req_fence,
>> +						 typeof(*req), fence);
>> +	u32 seqno;
>> +
>> +	seqno = req->ring->get_seqno(req->ring, false/*lazy_coherency*/);
>> +
>> +	return i915_seqno_passed(seqno, req->seqno);
>> +}
>> +
>> +static const char *i915_gem_request_get_driver_name(struct fence *req_fence)
>> +{
>> +	return "i915";
>> +}
>> +
>> +static const char *i915_gem_request_get_timeline_name(struct fence *req_fence)
>> +{
>> +	struct drm_i915_gem_request *req = container_of(req_fence,
>> +						 typeof(*req), fence);
>> +	return req->ring->name;
>> +}
>> +
>> +static const struct fence_ops i915_gem_request_fops = {
>> +	.enable_signaling	= i915_gem_request_enable_signaling,
>> +	.signaled		= i915_gem_request_is_completed,
>> +	.wait			= fence_default_wait,
>> +	.release		= i915_gem_request_free,
>> +	.get_driver_name	= i915_gem_request_get_driver_name,
>> +	.get_timeline_name	= i915_gem_request_get_timeline_name,
>> +};
>> +
>>  int i915_gem_request_alloc(struct intel_engine_cs *ring,
>>  			   struct intel_context *ctx,
>>  			   struct drm_i915_gem_request **req_out)
>> @@ -2659,7 +2700,6 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>>  	if (ret)
>>  		goto err;
>>  
>> -	kref_init(&req->ref);
>>  	req->i915 = dev_priv;
>>  	req->ring = ring;
>>  	req->ctx  = ctx;
>> @@ -2674,6 +2714,8 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>>  		goto err;
>>  	}
>>  
>> +	fence_init(&req->fence, &i915_gem_request_fops, &ring->fence_lock, ring->fence_context, req->seqno);
>> +
>>  	/*
>>  	 * Reserve space in the ring buffer for all the commands required to
>>  	 * eventually emit this request. This is to guarantee that the
>> @@ -4723,7 +4765,7 @@ i915_gem_init_hw(struct drm_device *dev)
>>  {
>>  	struct drm_i915_private *dev_priv = dev->dev_private;
>>  	struct intel_engine_cs *ring;
>> -	int ret, i, j;
>> +	int ret, i, j, fence_base;
>>  
>>  	if (INTEL_INFO(dev)->gen < 6 && !intel_enable_gtt())
>>  		return -EIO;
>> @@ -4793,12 +4835,16 @@ i915_gem_init_hw(struct drm_device *dev)
>>  	if (ret)
>>  		goto out;
>>  
>> +	fence_base = fence_context_alloc(I915_NUM_RINGS);
>> +
>>  	/* Now it is safe to go back round and do everything else: */
>>  	for_each_ring(ring, dev_priv, i) {
>>  		struct drm_i915_gem_request *req;
>>  
>>  		WARN_ON(!ring->default_context);
>>  
>> +		ring->fence_context = fence_base + i;
>> +
>>  		ret = i915_gem_request_alloc(ring, ring->default_context, &req);
>>  		if (ret) {
>>  			i915_gem_cleanup_ringbuffer(dev);
>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>> index 06180dc..b8c8f9b 100644
>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>> @@ -1920,6 +1920,7 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
>>  	ring->dev = dev;
>>  	INIT_LIST_HEAD(&ring->active_list);
>>  	INIT_LIST_HEAD(&ring->request_list);
>> +	spin_lock_init(&ring->fence_lock);
>>  	i915_gem_batch_pool_init(dev, &ring->batch_pool);
>>  	init_waitqueue_head(&ring->irq_queue);
>>  
>> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> index c9b081f..f4a6403 100644
>> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
>> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> @@ -2158,6 +2158,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
>>  	INIT_LIST_HEAD(&ring->request_list);
>>  	INIT_LIST_HEAD(&ring->execlist_queue);
>>  	INIT_LIST_HEAD(&ring->buffers);
>> +	spin_lock_init(&ring->fence_lock);
>>  	i915_gem_batch_pool_init(dev, &ring->batch_pool);
>>  	memset(ring->semaphore.sync_seqno, 0, sizeof(ring->semaphore.sync_seqno));
>>  
>> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
>> index 58b1976..4547645 100644
>> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
>> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
>> @@ -348,6 +348,9 @@ struct  intel_engine_cs {
>>  	 * to encode the command length in the header).
>>  	 */
>>  	u32 (*get_cmd_length_mask)(u32 cmd_header);
>> +
>> +	unsigned fence_context;
>> +	spinlock_t fence_lock;
>>  };
>>  
>>  bool intel_ring_initialized(struct intel_engine_cs *ring);
>>
> 
> Chris has an equivalent patch that does a little more (interrupt driven waits, custom i915 wait function, etc).  Can you review that instead assuming it's sufficient?
> 
> http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=f062e706740d87befb8e7cd7ea337f98f0b24f52

Ok given that Chris's stuff is more ambitious, and this has already been
out there a long time and seen a lot of review, I think we should go
ahead with this version first, and then rebase Chris's stuff on top.

So this one has my ack.

Jesse

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