Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> By taking advantage of the RCU protection of the task struct, we can find
> the appropriate signaler under the spinlock and then release the spinlock
> before waking the task and signaling the fence.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_irq.c | 32 +++++++++++++++++++++-----------
> 1 file changed, 21 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 46aaef5c1851..56a080bc4498 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1145,21 +1145,23 @@ static void ironlake_rps_change_irq_handler(struct drm_i915_private *dev_priv)
>
> static void notify_ring(struct intel_engine_cs *engine)
> {
> + const u32 seqno = intel_engine_get_seqno(engine);
> struct i915_request *rq = NULL;
> + struct task_struct *tsk = NULL;
> struct intel_wait *wait;
>
> - if (!engine->breadcrumbs.irq_armed)
> + if (unlikely(!engine->breadcrumbs.irq_armed))
> return;
>
> atomic_inc(&engine->irq_count);
> - set_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
> +
> + rcu_read_lock();
>
> spin_lock(&engine->breadcrumbs.irq_lock);
> wait = engine->breadcrumbs.irq_wait;
> if (wait) {
> - bool wakeup = engine->irq_seqno_barrier;
> -
> - /* We use a callback from the dma-fence to submit
> + /*
> + * We use a callback from the dma-fence to submit
> * requests after waiting on our own requests. To
> * ensure minimum delay in queuing the next request to
> * hardware, signal the fence now rather than wait for
> @@ -1170,19 +1172,22 @@ static void notify_ring(struct intel_engine_cs *engine)
> * and to handle coalescing of multiple seqno updates
> * and many waiters.
> */
> - if (i915_seqno_passed(intel_engine_get_seqno(engine),
> - wait->seqno)) {
> + if (i915_seqno_passed(seqno, wait->seqno)) {
> struct i915_request *waiter = wait->request;
>
> - wakeup = true;
> if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> &waiter->fence.flags) &&
> intel_wait_check_request(wait, waiter))
> rq = i915_request_get(waiter);
> - }
>
> - if (wakeup)
> - wake_up_process(wait->tsk);
> + tsk = wait->tsk;
> + } else {
> + if (engine->irq_seqno_barrier) {
> + set_bit(ENGINE_IRQ_BREADCRUMB,
> + &engine->irq_posted);
> + tsk = wait->tsk;
> + }
> + }
> } else {
> if (engine->breadcrumbs.irq_armed)
> __intel_engine_disarm_breadcrumbs(engine);
> @@ -1195,6 +1200,11 @@ static void notify_ring(struct intel_engine_cs *engine)
> i915_request_put(rq);
> }
>
> + if (tsk && tsk->state & TASK_NORMAL)
> + wake_up_process(tsk);
> +
> + rcu_read_unlock();
> +
> trace_intel_engine_notify(engine, wait);
> }
>
> --
> 2.18.0
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