On 4/15/2015 5:40 PM, Chris Wilson wrote:
On Wed, Apr 15, 2015 at 05:17:13PM +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. We may not need to
executed them, and this is why request->tail must be sampled before adding
these extra instructions.
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.
v2: Move overallocation to gen8_emit_request, and added note about
sampling request->tail in commit message (Chris).
v3: Remove redundant request->tail assignment in __i915_add_request, in
lrc mode this is already set in execlists_context_queue.
Do not add wa implementation details inside gem (Chris).
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Daniel <thomas.daniel@xxxxxxxxx>
Signed-off-by: Michel Thierry <michel.thierry@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem.c | 3 ++-
drivers/gpu/drm/i915/intel_lrc.c | 35 ++++++++++++++++++++++++++++++++++-
2 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3d5a5a8..980e17c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2400,10 +2400,11 @@ int __i915_add_request(struct intel_engine_cs *ring,
ret = ring->add_request(ring);
if (ret)
return ret;
+
+ request->tail = intel_ring_get_tail(ringbuf);
}
request->head = request_start;
- request->tail = intel_ring_get_tail(ringbuf);
/* Whilst this request exists, batch_obj will be on the
* active_list, and so will hold the active reference. Only when this
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index f4a5ef9..0296350 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -427,6 +427,26 @@ 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.
I actually think you can remove the == 1 and hence remove comment since
the wa is safe to apply in that case as well.
/* Apply the wa NOOPS to prevent ring:HEAD == rq:TAIL as we
* resubmit the request. See gen8_emit_request() for where we
* prepare the padding after the end of the request.
*/
Yes, it's safe to apply it after the request has been submitted multiple
times.
I'll change that and update the comment.
Thanks,
-Michel
+ */
+ 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,
@@ -1289,7 +1309,12 @@ static int gen8_emit_request(struct intel_ringbuffer *ringbuf,
u32 cmd;
int ret;
- ret = intel_logical_ring_begin(ringbuf, request->ctx, 6);
+ /*
+ * 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 (WaIdleLiteRestore).
+ */
+ ret = intel_logical_ring_begin(ringbuf, request->ctx, 8);
if (ret)
return ret;
@@ -1307,6 +1332,14 @@ static int gen8_emit_request(struct intel_ringbuffer *ringbuf,
intel_logical_ring_emit(ringbuf, MI_NOOP);
intel_logical_ring_advance_and_submit(ringbuf, request->ctx, request);
+ /*
+ * 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);
+
Ok, looks better.
-Chris
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