[PATCH 2/3] drm/i915/scheduler: emulate a scheduler for guc

Chris Wilson
2017-01-11T13:13:11Z

This emulates execlists on top of the GuC in order to defer submission of
requests to the hardware. This deferral allows time for high priority
requests to gazump their way to the head of the queue, however it nerfs
the GuC by converting it back into a simple execlist (where the CPU has
to wake up after every request to feed new commands into the GuC).

v2: Drop hack status - though iirc there is still a lockdep inversion
between fence and engine->timeline->lock (which is impossible as the
nesting only occurs on different fences - hopefully just requires some
judicious lockdep annotation)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
drivers/gpu/drm/i915/i915_guc_submission.c | 79 +++++++++++++++++++++++++++---
drivers/gpu/drm/i915/i915_irq.c | 4 +-
drivers/gpu/drm/i915/intel_lrc.c | 5 +-
3 files changed, 76 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 913d87358972..bdc9e2bc5eb9 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -350,7 +350,7 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
u32 freespace;
int ret;

- spin_lock(&client->wq_lock);
+ spin_lock_irq(&client->wq_lock);
freespace = CIRC_SPACE(client->wq_tail, desc->head, client->wq_size);
freespace -= client->wq_rsvd;
if (likely(freespace >= wqi_size)) {
@@ -360,7 +360,7 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
client->no_wq_space++;
ret = -EAGAIN;
}
- spin_unlock(&client->wq_lock);
+ spin_unlock_irq(&client->wq_lock);

return ret;
}
@@ -372,9 +372,9 @@ void i915_guc_wq_unreserve(struct drm_i915_gem_request *request)

GEM_BUG_ON(READ_ONCE(client->wq_rsvd) < wqi_size);

- spin_lock(&client->wq_lock);
+ spin_lock_irq(&client->wq_lock);
client->wq_rsvd -= wqi_size;
- spin_unlock(&client->wq_lock);
+ spin_unlock_irq(&client->wq_lock);
}

/* Construct a Work Item and append it to the GuC's Work Queue */
@@ -534,10 +534,74 @@ static void __i915_guc_submit(struct drm_i915_gem_request *rq)

static void i915_guc_submit(struct drm_i915_gem_request *rq)
{
- i915_gem_request_submit(rq);
+ __i915_gem_request_submit(rq);
__i915_guc_submit(rq);
}

+static bool i915_guc_dequeue(struct intel_engine_cs *engine)
+{
+ struct execlist_port *port = engine->execlist_port;
+ struct drm_i915_gem_request *last = port[0].request;
+ unsigned long flags;
+ struct rb_node *rb;
+ bool submit = false;
+
+ spin_lock_irqsave(&engine->timeline->lock, flags);
+ rb = engine->execlist_first;
+ while (rb) {
+ struct drm_i915_gem_request *cursor =
+ rb_entry(rb, typeof(*cursor), priotree.node);
+
+ if (last && cursor->ctx != last->ctx) {
+ if (port != engine->execlist_port)
+ break;
+
+ i915_gem_request_assign(&port->request, last);
+ dma_fence_enable_sw_signaling(&last->fence);
+ port++;
+ }
+
+ rb = rb_next(rb);
+ rb_erase(&cursor->priotree.node, &engine->execlist_queue);
+ RB_CLEAR_NODE(&cursor->priotree.node);
+ cursor->priotree.priority = INT_MAX;
+
+ i915_guc_submit(cursor);
+ last = cursor;
+ submit = true;
+ }
+ if (submit) {
+ i915_gem_request_assign(&port->request, last);
+ dma_fence_enable_sw_signaling(&last->fence);
+ engine->execlist_first = rb;
+ }
+ spin_unlock_irqrestore(&engine->timeline->lock, flags);
+
+ return submit;
+}
+
+static void i915_guc_irq_handler(unsigned long data)
+{
+ struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
+ struct execlist_port *port = engine->execlist_port;
+ struct drm_i915_gem_request *rq;
+ bool submit;
+
+ do {
+ rq = port[0].request;
+ while (rq && i915_gem_request_completed(rq)) {
+ i915_gem_request_put(rq);
+ rq = port[1].request;
+ port[0].request = rq;
+ port[1].request = NULL;
+ }
+
+ submit = false;
+ if (!port[1].request)
+ submit = i915_guc_dequeue(engine);
+ } while (submit);
+}
+
/*
* Everything below here is concerned with setup & teardown, and is
* therefore not part of the somewhat time-critical batch-submission
@@ -1428,8 +1492,9 @@ int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
for_each_engine(engine, dev_priv, id) {
struct drm_i915_gem_request *rq;

- engine->submit_request = i915_guc_submit;
- engine->schedule = NULL;
+ tasklet_init(&engine->irq_tasklet,
+ i915_guc_irq_handler,
+ (unsigned long)engine);

/* Replay the current set of previously submitted requests */
list_for_each_entry(rq, &engine->timeline->requests, link) {
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 75fb1f66cc0c..624267bebf56 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1341,8 +1341,10 @@ static void snb_gt_irq_handler(struct drm_i915_private *dev_priv,
static __always_inline void
gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
{
- if (iir & (GT_RENDER_USER_INTERRUPT << test_shift))
+ if (iir & (GT_RENDER_USER_INTERRUPT << test_shift)) {
+ tasklet_schedule(&engine->irq_tasklet);
notify_ring(engine);
+ }
if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift))
tasklet_schedule(&engine->irq_tasklet);
}
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index d9de455da131..33fe7e5c9364 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1352,7 +1352,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
DRM_DEBUG_DRIVER("Execlists enabled for %s\n", engine->name);

/* After a GPU reset, we may have requests to replay */
- if (!execlists_elsp_idle(engine)) {
+ if (!i915.enable_guc_submission && !execlists_elsp_idle(engine)) {
engine->execlist_port[0].count = 0;
engine->execlist_port[1].count = 0;
execlists_submit_ports(engine);
@@ -1420,9 +1420,6 @@ static void reset_common_ring(struct intel_engine_cs *engine,
request->ring->last_retired_head = -1;
intel_ring_update_space(request->ring);

- if (i915.enable_guc_submission)
- return;
-
/* Catch up with any missed context-switch interrupts */
I915_WRITE(RING_CONTEXT_STATUS_PTR(engine), _MASKED_FIELD(0xffff, 0));
if (request->ctx != port[0].request->ctx) {
--
2.11.0