Re: [Intel-gfx] [PATCH 2/5] drm/i915: Allow asynchronous waits on the i915_active barriers

[Tvrtko Ursulin]

On 06/04/2020 10:12, Chris Wilson wrote:
Allow the caller to also wait upon the barriers stored in i915_active.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
  drivers/gpu/drm/i915/i915_active.c | 60 ++++++++++++++++++++++++++++++
  drivers/gpu/drm/i915/i915_active.h |  1 +
  2 files changed, 61 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_active.c 
b/drivers/gpu/drm/i915/i915_active.c
index d5e24be759f7..048ab9edd2c2 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -542,6 +542,55 @@ static int __await_active(struct i915_active_fence *active,
        return 0;
  }
  
+struct wait_barrier {
+       struct wait_queue_entry base;
+       struct i915_active *ref;
+};
+
+static int
+barrier_wake(wait_queue_entry_t *wq, unsigned int mode, int flags, void *key)
+{
+       struct wait_barrier *wb = container_of(wq, typeof(*wb), base);
+
+       if (i915_active_is_idle(wb->ref)) { /* shared waitqueue, must check! */

Who shares it?

+               list_del(&wq->entry);
+               i915_sw_fence_complete(wq->private);
+               kfree(wq);
+       }
+
+       return 0;
+}
+
+static int __await_barrier(struct i915_active *ref, struct i915_sw_fence 
*fence)
+{
+       struct wait_barrier *wb;
+
+       wb = kmalloc(sizeof(*wb), GFP_KERNEL);
+       if (unlikely(!wb))
+               return -ENOMEM;
+
+       if (!i915_active_acquire_if_busy(ref)) {
+               kfree(wb);
+               return 0;
+       }
+
+       if (!i915_sw_fence_await(fence)) {
+               kfree(wb);
+               i915_active_release(ref);
+               return -EINVAL;
+       }
+
+       wb->base.flags = 0;
+       wb->base.func = barrier_wake;
+       wb->base.private = fence;
+       wb->ref = ref;
+
+       add_wait_queue(__var_waitqueue(ref), &wb->base);
+
+       i915_active_release(ref);
+       return 0;
+}
+
  static int await_active(struct i915_active *ref,
                        unsigned int flags,
                        int (*fn)(void *arg, struct dma_fence *fence),
@@ -570,6 +619,16 @@ static int await_active(struct i915_active *ref,
                        return err;
        }
  
+	if (flags & I915_ACTIVE_AWAIT_BARRIER) {
+               err = flush_lazy_signals(ref);
+               if (err)
+                       return err;
+
+               err = __await_barrier(ref, arg);
+               if (err)
+                       return err;


Could have a single set of active_acquire_if_busy/release over the 
previous and this new block. Not sure if that would help with any 
atomicity concerns, or if there are such.

 +      }
+
        return 0;
  }
  
@@ -582,6 +641,7 @@ int i915_request_await_active(struct i915_request *rq,
                              struct i915_active *ref,
                              unsigned int flags)
  {
+       GEM_BUG_ON(flags & I915_ACTIVE_AWAIT_BARRIER);

Why is this an error?

        return await_active(ref, flags, rq_await_fence, rq);
  }
  
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index ffafaa78c494..cf4058150966 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -195,6 +195,7 @@ int i915_request_await_active(struct i915_request *rq,
                              unsigned int flags);
  #define I915_ACTIVE_AWAIT_EXCL BIT(0)
  #define I915_ACTIVE_AWAIT_ACTIVE BIT(1)
+#define I915_ACTIVE_AWAIT_BARRIER BIT(2)
  
  int i915_active_acquire(struct i915_active *ref);
  bool i915_active_acquire_if_busy(struct i915_active *ref);


Regards,

Tvrtko
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