drm/i915: Identify active requests

To allow requests to forgo a common execution timeline, one question we
need to be able to answer is "is this request running?". To track
whether a request has started on HW, we can emit a breadcrumb at the
beginning of the request and check its timeline's HWSP to see if the
breadcrumb has advanced past the start of this request. (This is in
contrast to the global timeline where we need only ask if we are on the
global timeline and if the timeline has advanced past the end of the
previous request.)

There is still confusion from a preempted request, which has already
started but relinquished the HW to a high priority request. For the
common case, this discrepancy should be negligible. However, for
identification of hung requests, knowing which one was running at the
time of the hang will be much more important.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190129185452.20989-2-chris@chris-wilson.co.uk

1 files changed, 34 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index fdbb3fe8eac9..5db16dd8e844 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -624,7 +624,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		 * WaIdleLiteRestore:bdw,skl
 		 * Apply the wa NOOPs to prevent
 		 * ring:HEAD == rq:TAIL as we resubmit the
-		 * request. See gen8_emit_breadcrumb() for
+		 * request. See gen8_emit_fini_breadcrumb() for
 		 * where we prepare the padding after the
 		 * end of the request.
 		 */
@@ -1283,6 +1283,34 @@ execlists_context_pin(struct intel_engine_cs *engine,
 	return __execlists_context_pin(engine, ctx, ce);
 }
 
+static int gen8_emit_init_breadcrumb(struct i915_request *rq)
+{
+	u32 *cs;
+
+	GEM_BUG_ON(!rq->timeline->has_initial_breadcrumb);
+
+	cs = intel_ring_begin(rq, 6);
+	if (IS_ERR(cs))
+		return PTR_ERR(cs);
+
+	/*
+	 * Check if we have been preempted before we even get started.
+	 *
+	 * After this point i915_request_started() reports true, even if
+	 * we get preempted and so are no longer running.
+	 */
+	*cs++ = MI_ARB_CHECK;
+	*cs++ = MI_NOOP;
+
+	*cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
+	*cs++ = rq->timeline->hwsp_offset;
+	*cs++ = 0;
+	*cs++ = rq->fence.seqno - 1;
+
+	intel_ring_advance(rq, cs);
+	return 0;
+}
+
 static int emit_pdps(struct i915_request *rq)
 {
 	const struct intel_engine_cs * const engine = rq->engine;
@@ -2039,7 +2067,7 @@ static u32 *gen8_emit_wa_tail(struct i915_request *request, u32 *cs)
 	return cs;
 }
 
-static u32 *gen8_emit_breadcrumb(struct i915_request *request, u32 *cs)
+static u32 *gen8_emit_fini_breadcrumb(struct i915_request *request, u32 *cs)
 {
 	/* w/a: bit 5 needs to be zero for MI_FLUSH_DW address. */
 	BUILD_BUG_ON(I915_GEM_HWS_INDEX_ADDR & (1 << 5));
@@ -2061,7 +2089,7 @@ static u32 *gen8_emit_breadcrumb(struct i915_request *request, u32 *cs)
 	return gen8_emit_wa_tail(request, cs);
 }
 
-static u32 *gen8_emit_breadcrumb_rcs(struct i915_request *request, u32 *cs)
+static u32 *gen8_emit_fini_breadcrumb_rcs(struct i915_request *request, u32 *cs)
 {
 	cs = gen8_emit_ggtt_write_rcs(cs,
 				      request->fence.seqno,
@@ -2176,7 +2204,8 @@ logical_ring_default_vfuncs(struct intel_engine_cs *engine)
 	engine->request_alloc = execlists_request_alloc;
 
 	engine->emit_flush = gen8_emit_flush;
-	engine->emit_breadcrumb = gen8_emit_breadcrumb;
+	engine->emit_init_breadcrumb = gen8_emit_init_breadcrumb;
+	engine->emit_fini_breadcrumb = gen8_emit_fini_breadcrumb;
 
 	engine->set_default_submission = intel_execlists_set_default_submission;
 
@@ -2289,7 +2318,7 @@ int logical_render_ring_init(struct intel_engine_cs *engine)
 	/* Override some for render ring. */
 	engine->init_context = gen8_init_rcs_context;
 	engine->emit_flush = gen8_emit_flush_render;
-	engine->emit_breadcrumb = gen8_emit_breadcrumb_rcs;
+	engine->emit_fini_breadcrumb = gen8_emit_fini_breadcrumb_rcs;
 
 	ret = logical_ring_init(engine);
 	if (ret)