Re: [PATCH 05/10] drm/i915: Mark up "sentinel" requests

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On 10/10/2019 08:14, Chris Wilson wrote:
Sometimes we want to emit a terminator request, a request that flushes
the pipeline and allows no request to come after it. This can be used
for a "preempt-to-idle" to ensure that upon processing the
context-switch to that request, all other active contexts have been
flushed.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gt/intel_lrc.c |  6 ++++++
  drivers/gpu/drm/i915/i915_request.h | 10 ++++++++--
  2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index aa52e5f34dab..eb99f1e804f7 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1253,6 +1253,9 @@ static bool can_merge_rq(const struct i915_request *prev,
  	if (i915_request_completed(next))
  		return true;
+ if (i915_request_has_sentinel(prev))
+		return false;
+
  	if (!can_merge_ctx(prev->hw_context, next->hw_context))
  		return false;
@@ -1724,6 +1727,9 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
  				if (last->hw_context == rq->hw_context)
  					goto done;
+ if (i915_request_has_sentinel(last))
+					goto done;
+
  				/*
  				 * If GVT overrides us we only ever submit
  				 * port[0], leaving port[1] empty. Note that we
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index 6a95242b280d..96991d64759c 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -216,8 +216,9 @@ struct i915_request {
  	unsigned long emitted_jiffies;
unsigned long flags;
-#define I915_REQUEST_WAITBOOST BIT(0)
-#define I915_REQUEST_NOPREEMPT BIT(1)
+#define I915_REQUEST_WAITBOOST	BIT(0)
+#define I915_REQUEST_NOPREEMPT	BIT(1)
+#define I915_REQUEST_SENTINEL	BIT(2)
/** timeline->request entry for this request */
  	struct list_head link;
@@ -440,6 +441,11 @@ static inline bool i915_request_has_nopreempt(const struct i915_request *rq)
  	return unlikely(rq->flags & I915_REQUEST_NOPREEMPT);
  }
+static inline bool i915_request_has_sentinel(const struct i915_request *rq)
+{
+	return unlikely(rq->flags & I915_REQUEST_SENTINEL);
+}
+
  static inline struct intel_timeline *
  i915_request_timeline(struct i915_request *rq)
  {


Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko
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