On 4/10/2015 11:01 AM, Daniel Vetter wrote:
On Fri, Apr 10, 2015 at 10:32:33AM +0100, Michel Thierry wrote:
WaIdleLiteRestore is an execlists-only workaround, and requires the driver
to ensure that any context always has HEAD!=TAIL when attempting lite
restore.
Add two extra MI_NOOP instructions at the end of each request, but keep
the requests tail pointing before the MI_NOOPs.
If we submit a context to the ELSP which has previously been submitted,
move the tail pointer past the MI_NOOPs. This ensures HEAD!=TAIL.
Signed-off-by: Thomas Daniel <thomas.daniel@xxxxxxxxx>
Signed-off-by: Michel Thierry <michel.thierry@xxxxxxxxx>
Is there an igt to provoke this? I'm thinking of submitting tiny noop
batches on 2 alternating contexts. That should be able to make this go
boom pretty reliable, we only need a slight delay in processing the
execlist completion interrupt.
-Daniel
I've seen it when running multiple contexts in parallel or when the
wa-batchbuffer was enabled.
I'll write an igt for it, we only need several small batches queued to
trigger the light restore.
--Michel
---
drivers/gpu/drm/i915/i915_gem.c | 11 +++++++++++
drivers/gpu/drm/i915/intel_lrc.c | 29 +++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ca522c9..a44070a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2382,6 +2382,17 @@ int __i915_add_request(struct intel_engine_cs *ring,
request->head = request_start;
request->tail = intel_ring_get_tail(ringbuf);
+ if (i915.enable_execlists &&
+ (IS_GEN8(ring->dev) || IS_GEN9(ring->dev))) {
+ /*
+ * Here we add two extra NOOPs as padding to avoid
+ * lite restore of a context with HEAD==TAIL.
+ */
+ intel_logical_ring_emit(ringbuf, MI_NOOP);
+ intel_logical_ring_emit(ringbuf, MI_NOOP);
+ intel_logical_ring_advance(ringbuf);
+ }
+
/* Whilst this request exists, batch_obj will be on the
* active_list, and so will hold the active reference. Only when this
* request is retired will the the batch_obj be moved onto the
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index f18f96c..8acedca 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -413,6 +413,26 @@ static void execlists_context_unqueue(struct intel_engine_cs *ring)
}
}
+ if (IS_GEN8(ring->dev) || IS_GEN9(ring->dev)) {
+ /*
+ * WaIdleLiteRestore: make sure we never cause a lite
+ * restore with HEAD==TAIL
+ */
+ if (req0 && req0->elsp_submitted == 1) {
+ /*
+ * Consume the buffer NOOPs to ensure HEAD != TAIL when
+ * submitting. elsp_submitted can only be >1 after
+ * reset, in which case we don't need the workaround as
+ * a lite restore will not occur.
+ */
+ struct intel_ringbuffer *ringbuf;
+
+ ringbuf = req0->ctx->engine[ring->id].ringbuf;
+ req0->tail += 8;
+ req0->tail &= ringbuf->size - 1;
+ }
+ }
+
WARN_ON(req1 && req1->elsp_submitted);
execlists_submit_contexts(ring, req0->ctx, req0->tail,
@@ -829,6 +849,15 @@ static int intel_logical_ring_begin(struct intel_ringbuffer *ringbuf,
struct drm_i915_private *dev_priv = dev->dev_private;
int ret;
+ if (IS_GEN8(dev) || IS_GEN9(dev)) {
+ /*
+ * Reserve space for 2 NOOPs at the end of each request to be
+ * used as a workaround for not being allowed to do lite
+ * restore with HEAD==TAIL.
+ */
+ num_dwords += 2;
+ }
+
ret = i915_gem_check_wedge(&dev_priv->gpu_error,
dev_priv->mm.interruptible);
if (ret)
--
2.1.1
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