If we are waiting for the currently executing request, we have a good
idea that it will be completed in the very near future and so want to
cap the CPU_DMA_LATENCY to ensure that we wake up the client quickly.
v2: Not allowed to block in kmalloc after setting TASK_INTERRUPTIBLE.
v3: Avoid the blocking notifier as well for TASK_INTERRUPTIBLE
v4: Beautification?
v5: And ignore the preemptibility of queue_work before schedule.
v6: Use highpri wq to keep our pm_qos window as small as possible.
Testcase: igt/gem_sync/store-default
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Eero Tamminen <eero.t.tamminen@xxxxxxxxx>
Cc: Francisco Jerez <currojerez@xxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_request.c | 59 +++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 5c2c93cbab12..67fd2ec75d78 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1258,6 +1258,58 @@ static bool __i915_wait_request_check_and_reset(struct i915_request *request)
return true;
}
+struct wait_dma_qos {
+ struct pm_qos_request req;
+ struct work_struct add, del;
+};
+
+static void __wait_dma_qos_add(struct work_struct *work)
+{
+ struct wait_dma_qos *qos = container_of(work, typeof(*qos), add);
+
+ pm_qos_add_request(&qos->req, PM_QOS_CPU_DMA_LATENCY, 50);
+}
+
+static void __wait_dma_qos_del(struct work_struct *work)
+{
+ struct wait_dma_qos *qos = container_of(work, typeof(*qos), del);
+
+ if (!cancel_work_sync(&qos->add))
+ pm_qos_remove_request(&qos->req);
+
+ kfree(qos);
+}
+
+static struct wait_dma_qos *wait_dma_qos_add(void)
+{
+ struct wait_dma_qos *qos;
+
+ /* Called under TASK_INTERRUPTIBLE, so not allowed to sleep/block. */
+ qos = kzalloc(sizeof(*qos), GFP_NOWAIT | __GFP_NOWARN);
+ if (!qos)
+ return NULL;
+
+ INIT_WORK(&qos->add, __wait_dma_qos_add);
+ INIT_WORK(&qos->del, __wait_dma_qos_del);
+
+ /*
+ * Schedule the enabling work on the local cpu so that it should only
+ * take effect if we actually sleep. If schedule() short circuits due to
+ * our request already being completed, we should then be able to cancel
+ * the work before it is even run.
+ */
+ queue_work_on(raw_smp_processor_id(), system_highpri_wq, &qos->add);
+
+ return qos;
+}
+
+static void wait_dma_qos_del(struct wait_dma_qos *qos)
+{
+ /* Defer to worker so not incur extra latency for our woken client. */
+ if (qos)
+ queue_work(system_highpri_wq, &qos->del);
+}
+
/**
* i915_request_wait - wait until execution of request has finished
* @rq: the request to wait upon
@@ -1286,6 +1338,7 @@ long i915_request_wait(struct i915_request *rq,
wait_queue_head_t *errq = &rq->i915->gpu_error.wait_queue;
DEFINE_WAIT_FUNC(reset, default_wake_function);
DEFINE_WAIT_FUNC(exec, default_wake_function);
+ struct wait_dma_qos *qos = NULL;
struct intel_wait wait;
might_sleep();
@@ -1363,6 +1416,11 @@ long i915_request_wait(struct i915_request *rq,
break;
}
+ if (!qos &&
+ i915_seqno_passed(intel_engine_get_seqno(rq->engine),
+ wait.seqno - 1))
+ qos = wait_dma_qos_add();
+
timeout = io_schedule_timeout(timeout);
if (intel_wait_complete(&wait) &&
@@ -1412,6 +1470,7 @@ long i915_request_wait(struct i915_request *rq,
if (flags & I915_WAIT_LOCKED)
remove_wait_queue(errq, &reset);
remove_wait_queue(&rq->execute, &exec);
+ wait_dma_qos_del(qos);
trace_i915_request_wait_end(rq);
return timeout;
--
2.18.0
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