Re: [PATCH v2 05/14] drm/i915: Deconstruct execute fence

Tvrtko Ursulin
2017-02-17T14:26:11Z

On 14/02/2017 09:54, Chris Wilson wrote:
> On reflection, we are only using the execute fence as a waitqueue on the
> global_seqno and not using it for dependency tracking between fences
> (unlike the submit and dma fences). By only treating it as a waitqueue,
> we can then treat it similar to the other waitqueues durin submit,

during

> making the code simpler.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
> drivers/gpu/drm/i915/i915_gem_request.c | 47 +++++++--------------------------
> drivers/gpu/drm/i915/i915_gem_request.h | 10 +------
> 2 files changed, 11 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 001fc9fedf49..bb59acaa8a34 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -69,7 +69,6 @@ static void i915_fence_release(struct dma_fence *fence)
> * caught trying to reuse dead objects.
> */
> i915_sw_fence_fini(&req->submit);
> - i915_sw_fence_fini(&req->execute);
>
> kmem_cache_free(req->i915->requests, req);
> }
> @@ -211,7 +210,6 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
>
> lockdep_assert_held(&request->i915->drm.struct_mutex);
> GEM_BUG_ON(!i915_sw_fence_signaled(&request->submit));
> - GEM_BUG_ON(!i915_sw_fence_signaled(&request->execute));
> GEM_BUG_ON(!i915_gem_request_completed(request));
>
> GEM_BUG_ON(!request->i915->gt.active_requests);
> @@ -422,7 +420,7 @@ void __i915_gem_request_submit(struct drm_i915_gem_request *request)
> list_move_tail(&request->link, &timeline->requests);
> spin_unlock(&request->timeline->lock);
>
> - i915_sw_fence_commit(&request->execute);
> + wake_up_all(&request->execute);
> }
>
> void i915_gem_request_submit(struct drm_i915_gem_request *request)
> @@ -457,24 +455,6 @@ submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
> return NOTIFY_DONE;
> }
>
> -static int __i915_sw_fence_call
> -execute_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
> -{
> - struct drm_i915_gem_request *request =
> - container_of(fence, typeof(*request), execute);
> -
> - switch (state) {
> - case FENCE_COMPLETE:
> - break;
> -
> - case FENCE_FREE:
> - i915_gem_request_put(request);
> - break;
> - }
> -
> - return NOTIFY_DONE;
> -}
> -
> /**
> * i915_gem_request_alloc - allocate a request structure
> *
> @@ -567,13 +547,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
>
> /* We bump the ref for the fence chain */
> i915_sw_fence_init(&i915_gem_request_get(req)->submit, submit_notify);
> - i915_sw_fence_init(&i915_gem_request_get(req)->execute, execute_notify);
> -
> - /* Ensure that the execute fence completes after the submit fence -
> - * as we complete the execute fence from within the submit fence
> - * callback, its completion would otherwise be visible first.
> - */
> - i915_sw_fence_await_sw_fence(&req->execute, &req->submit, &req->execq);
> + init_waitqueue_head(&req->execute);
>
> i915_priotree_init(&req->priotree);
>
> @@ -1015,6 +989,7 @@ long i915_wait_request(struct drm_i915_gem_request *req,
> TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
> wait_queue_head_t *errq = &req->i915->gpu_error.wait_queue;
> DEFINE_WAIT(reset);
> + DEFINE_WAIT(exec);
> struct intel_wait wait;
>
> might_sleep();
> @@ -1036,12 +1011,11 @@ long i915_wait_request(struct drm_i915_gem_request *req,
> if (flags & I915_WAIT_LOCKED)
> add_wait_queue(errq, &reset);
>
> - if (!i915_sw_fence_done(&req->execute)) {
> - DEFINE_WAIT(exec);
> -
> + reset_wait_queue(&req->execute, &exec);
> + if (!req->global_seqno) {
> do {
> - prepare_to_wait(&req->execute.wait, &exec, state);

Somehow I missed the moment when reset_wait_queue was introduced. But
why you can't just use prepare_to_wait here?

Otherwise looks OK.

Regards,

Tvrtko

> - if (i915_sw_fence_done(&req->execute))
> + set_current_state(state);
> + if (req->global_seqno)
> break;
>
> if (flags & I915_WAIT_LOCKED &&
> @@ -1064,15 +1038,14 @@ long i915_wait_request(struct drm_i915_gem_request *req,
>
> timeout = io_schedule_timeout(timeout);
> } while (1);
> - finish_wait(&req->execute.wait, &exec);
> + finish_wait(&req->execute, &exec);
>
> if (timeout < 0)
> goto complete;
>
> - GEM_BUG_ON(!i915_sw_fence_done(&req->execute));
> + GEM_BUG_ON(!req->global_seqno);
> }
> - GEM_BUG_ON(!i915_sw_fence_done(&req->submit));
> - GEM_BUG_ON(!req->global_seqno);
> + GEM_BUG_ON(!i915_sw_fence_signaled(&req->submit));
>
> /* Optimistic short spin before touching IRQs */
> if (i915_spin_request(req, state, 5))
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
> index 9049936c571c..467d3e13fce0 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.h
> +++ b/drivers/gpu/drm/i915/i915_gem_request.h
> @@ -119,18 +119,10 @@ struct drm_i915_gem_request {
> * The submit fence is used to await upon all of the request's
> * dependencies. When it is signaled, the request is ready to run.
> * It is used by the driver to then queue the request for execution.
> - *
> - * The execute fence is used to signal when the request has been
> - * sent to hardware.
> - *
> - * It is illegal for the submit fence of one request to wait upon the
> - * execute fence of an earlier request. It should be sufficient to
> - * wait upon the submit fence of the earlier request.
> */
> struct i915_sw_fence submit;
> - struct i915_sw_fence execute;
> wait_queue_t submitq;
> - wait_queue_t execq;
> + wait_queue_head_t execute;
>
> /* A list of everyone we wait upon, and everyone who waits upon us.
> * Even though we will not be submitted to the hardware before the
>