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drm/i915: Only enqueue already completed requests

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If we are asked to submit a completed request, just move it onto the
active-list without modifying it's payload. If we try to emit the
modified payload of a completed request, we risk racing with the
ring->head update during retirement which may advance the head past our
breadcrumb and so we generate a warning for the emission being behind
the RING_HEAD.

v2: Commentary for the sneaky, shared responsibility between functions.
v3: Spelling mistakes and bonus assertion

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/20190923110056.15176-3-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson
2019-09-23 12:00:55 +01:00
parent 3231f8c011
commit c0bb487dc1
3 changed files with 74 additions and 38 deletions
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44
drivers/gpu/drm/i915/i915_request.c
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@@ -377,9 +377,10 @@ __i915_request_await_execution(struct i915_request *rq,
return 0;
}
void __i915_request_submit(struct i915_request *request)
bool __i915_request_submit(struct i915_request *request)
{
struct intel_engine_cs *engine = request->engine;
bool result = false;
GEM_TRACE("%s fence %llx:%lld, current %d\n",
engine->name,
@@ -389,6 +390,25 @@ void __i915_request_submit(struct i915_request *request)
GEM_BUG_ON(!irqs_disabled());
lockdep_assert_held(&engine->active.lock);
/*
* With the advent of preempt-to-busy, we frequently encounter
* requests that we have unsubmitted from HW, but left running
* until the next ack and so have completed in the meantime. On
* resubmission of that completed request, we can skip
* updating the payload, and execlists can even skip submitting
* the request.
*
* We must remove the request from the caller's priority queue,
* and the caller must only call us when the request is in their
* priority queue, under the active.lock. This ensures that the
* request has *not* yet been retired and we can safely move
* the request into the engine->active.list where it will be
* dropped upon retiring. (Otherwise if resubmit a *retired*
* request, this would be a horrible use-after-free.)
*/
if (i915_request_completed(request))
goto xfer;
if (i915_gem_context_is_banned(request->gem_context))
i915_request_skip(request, -EIO);
@@ -412,13 +432,18 @@ void __i915_request_submit(struct i915_request *request)
i915_sw_fence_signaled(&request->semaphore))
engine->saturated |= request->sched.semaphores;
/* We may be recursing from the signal callback of another i915 fence */
engine->emit_fini_breadcrumb(request,
request->ring->vaddr + request->postfix);
trace_i915_request_execute(request);
engine->serial++;
result = true;
xfer: /* We may be recursing from the signal callback of another i915 fence */
spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);
list_move_tail(&request->sched.link, &engine->active.requests);
GEM_BUG_ON(test_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags));
set_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags);
if (!test_and_set_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags))
list_move_tail(&request->sched.link, &engine->active.requests);
if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags) &&
@@ -429,12 +454,7 @@ void __i915_request_submit(struct i915_request *request)
spin_unlock(&request->lock);
engine->emit_fini_breadcrumb(request,
request->ring->vaddr + request->postfix);
engine->serial++;
trace_i915_request_execute(request);
return result;
}
void i915_request_submit(struct i915_request *request)