[PATCH 34/34] drm/i915: Replace global_seqno with a hangcheck heartbeat seqno

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To determine whether an engine has 'struck', we simply check whether or
not is still on the same seqno for several seconds. To keep this simple
mechanism intact over the loss of a global seqno, we can simply add a
new global heartbeat seqno instead. As we cannot know the sequence in
which requests will then be completed, we use a primitive random number
generator instead (with a cycle long enough to not matter over an
interval of a few thousand requests between hangcheck samples).

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_debugfs.c     |  7 ++++---
 drivers/gpu/drm/i915/intel_engine_cs.c  |  5 +++--
 drivers/gpu/drm/i915/intel_hangcheck.c  |  6 +++---
 drivers/gpu/drm/i915/intel_lrc.c        | 19 +++++++++++++++--
 drivers/gpu/drm/i915/intel_ringbuffer.c | 28 +++++++++++++++++++------
 drivers/gpu/drm/i915/intel_ringbuffer.h | 19 ++++++++++++++++-
 6 files changed, 67 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index c2aaf010c3d1..16a9384de478 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1297,7 +1297,7 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 	with_intel_runtime_pm(dev_priv, wakeref) {
 		for_each_engine(engine, dev_priv, id) {
 			acthd[id] = intel_engine_get_active_head(engine);
-			seqno[id] = intel_engine_get_seqno(engine);
+			seqno[id] = intel_engine_get_hangcheck_seqno(engine);
 		}
 
 		intel_engine_get_instdone(dev_priv->engine[RCS], &instdone);
@@ -1317,8 +1317,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 	for_each_engine(engine, dev_priv, id) {
 		seq_printf(m, "%s:\n", engine->name);
 		seq_printf(m, "\tseqno = %x [current %x, last %x], %dms ago\n",
-			   engine->hangcheck.seqno, seqno[id],
-			   intel_engine_last_submit(engine),
+			   engine->hangcheck.last_seqno,
+			   seqno[id],
+			   engine->hangcheck.next_seqno,
 			   jiffies_to_msecs(jiffies -
 					    engine->hangcheck.action_timestamp));
 
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 1d9157bf96ae..f631ad23a702 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1439,10 +1439,11 @@ void intel_engine_dump(struct intel_engine_cs *engine,
 	if (i915_terminally_wedged(&engine->i915->gpu_error))
 		drm_printf(m, "*** WEDGED ***\n");
 
-	drm_printf(m, "\tcurrent seqno %x, last %x, hangcheck %x [%d ms]\n",
+	drm_printf(m, "\tcurrent seqno %x, last %x, hangcheck %x/%x [%d ms]\n",
 		   intel_engine_get_seqno(engine),
 		   intel_engine_last_submit(engine),
-		   engine->hangcheck.seqno,
+		   engine->hangcheck.last_seqno,
+		   engine->hangcheck.next_seqno,
 		   jiffies_to_msecs(jiffies - engine->hangcheck.action_timestamp));
 	drm_printf(m, "\tReset count: %d (global %d)\n",
 		   i915_reset_engine_count(error, engine),
diff --git a/drivers/gpu/drm/i915/intel_hangcheck.c b/drivers/gpu/drm/i915/intel_hangcheck.c
index a219c796e56d..e04b2560369e 100644
--- a/drivers/gpu/drm/i915/intel_hangcheck.c
+++ b/drivers/gpu/drm/i915/intel_hangcheck.c
@@ -133,21 +133,21 @@ static void hangcheck_load_sample(struct intel_engine_cs *engine,
 				  struct hangcheck *hc)
 {
 	hc->acthd = intel_engine_get_active_head(engine);
-	hc->seqno = intel_engine_get_seqno(engine);
+	hc->seqno = intel_engine_get_hangcheck_seqno(engine);
 }
 
 static void hangcheck_store_sample(struct intel_engine_cs *engine,
 				   const struct hangcheck *hc)
 {
 	engine->hangcheck.acthd = hc->acthd;
-	engine->hangcheck.seqno = hc->seqno;
+	engine->hangcheck.last_seqno = hc->seqno;
 }
 
 static enum intel_engine_hangcheck_action
 hangcheck_get_action(struct intel_engine_cs *engine,
 		     const struct hangcheck *hc)
 {
-	if (engine->hangcheck.seqno != hc->seqno)
+	if (engine->hangcheck.last_seqno != hc->seqno)
 		return ENGINE_ACTIVE_SEQNO;
 
 	if (intel_engine_is_idle(engine))
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index b59cfec1d5d4..2864a9f542aa 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -178,6 +178,12 @@ static inline u32 intel_hws_seqno_address(struct intel_engine_cs *engine)
 		I915_GEM_HWS_INDEX_ADDR);
 }
 
+static inline u32 intel_hws_hangcheck_address(struct intel_engine_cs *engine)
+{
+	return (i915_ggtt_offset(engine->status_page.vma) +
+		I915_GEM_HWS_HANGCHECK_ADDR);
+}
+
 static inline struct i915_priolist *to_priolist(struct rb_node *rb)
 {
 	return rb_entry(rb, struct i915_priolist, node);
@@ -2106,6 +2112,10 @@ static void gen8_emit_fini_breadcrumb(struct i915_request *request, u32 *cs)
 				  request->fence.seqno,
 				  i915_timeline_seqno_address(request->timeline));
 
+	cs = gen8_emit_ggtt_write(cs,
+				  intel_engine_next_hangcheck_seqno(request->engine),
+				  intel_hws_hangcheck_address(request->engine));
+
 	cs = gen8_emit_ggtt_write(cs,
 				  request->global_seqno,
 				  intel_hws_seqno_address(request->engine));
@@ -2118,7 +2128,7 @@ static void gen8_emit_fini_breadcrumb(struct i915_request *request, u32 *cs)
 
 	gen8_emit_wa_tail(request, cs);
 }
-static const int gen8_emit_fini_breadcrumb_sz = 10 + WA_TAIL_DWORDS;
+static const int gen8_emit_fini_breadcrumb_sz = 14 + WA_TAIL_DWORDS;
 
 static void gen8_emit_fini_breadcrumb_rcs(struct i915_request *request, u32 *cs)
 {
@@ -2131,6 +2141,11 @@ static void gen8_emit_fini_breadcrumb_rcs(struct i915_request *request, u32 *cs)
 				      PIPE_CONTROL_FLUSH_ENABLE |
 				      PIPE_CONTROL_CS_STALL);
 
+	cs = gen8_emit_ggtt_write_rcs(cs,
+				      intel_engine_next_hangcheck_seqno(request->engine),
+				      intel_hws_hangcheck_address(request->engine),
+				      PIPE_CONTROL_CS_STALL);
+
 	cs = gen8_emit_ggtt_write_rcs(cs,
 				      request->global_seqno,
 				      intel_hws_seqno_address(request->engine),
@@ -2144,7 +2159,7 @@ static void gen8_emit_fini_breadcrumb_rcs(struct i915_request *request, u32 *cs)
 
 	gen8_emit_wa_tail(request, cs);
 }
-static const int gen8_emit_fini_breadcrumb_rcs_sz = 14 + WA_TAIL_DWORDS;
+static const int gen8_emit_fini_breadcrumb_rcs_sz = 20 + WA_TAIL_DWORDS;
 
 static int gen8_init_rcs_context(struct i915_request *rq)
 {
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index bd44ea41d7ca..13f2836bb7b4 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -456,17 +456,20 @@ static void gen6_xcs_emit_breadcrumb(struct i915_request *rq, u32 *cs)
 	*cs++ = I915_GEM_HWS_SEQNO_ADDR | MI_FLUSH_DW_USE_GTT;
 	*cs++ = rq->fence.seqno;
 
+	*cs++ = MI_FLUSH_DW | MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
+	*cs++ = I915_GEM_HWS_HANGCHECK_ADDR | MI_FLUSH_DW_USE_GTT;
+	*cs++ = intel_engine_next_hangcheck_seqno(rq->engine);
+
 	*cs++ = MI_FLUSH_DW | MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
 	*cs++ = I915_GEM_HWS_INDEX_ADDR | MI_FLUSH_DW_USE_GTT;
 	*cs++ = rq->global_seqno;
 
 	*cs++ = MI_USER_INTERRUPT;
-	*cs++ = MI_NOOP;
 
 	rq->tail = intel_ring_offset(rq, cs);
 	assert_ring_tail_valid(rq->ring, rq->tail);
 }
-static const int gen6_xcs_emit_breadcrumb_sz = 8;
+static const int gen6_xcs_emit_breadcrumb_sz = 10;
 
 #define GEN7_XCS_WA 32
 static void gen7_xcs_emit_breadcrumb(struct i915_request *rq, u32 *cs)
@@ -477,6 +480,10 @@ static void gen7_xcs_emit_breadcrumb(struct i915_request *rq, u32 *cs)
 	*cs++ = I915_GEM_HWS_SEQNO_ADDR | MI_FLUSH_DW_USE_GTT;
 	*cs++ = rq->fence.seqno;
 
+	*cs++ = MI_FLUSH_DW | MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
+	*cs++ = I915_GEM_HWS_HANGCHECK_ADDR | MI_FLUSH_DW_USE_GTT;
+	*cs++ = intel_engine_next_hangcheck_seqno(rq->engine);
+
 	*cs++ = MI_FLUSH_DW | MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
 	*cs++ = I915_GEM_HWS_INDEX_ADDR | MI_FLUSH_DW_USE_GTT;
 	*cs++ = rq->global_seqno;
@@ -492,11 +499,12 @@ static void gen7_xcs_emit_breadcrumb(struct i915_request *rq, u32 *cs)
 	*cs++ = 0;
 
 	*cs++ = MI_USER_INTERRUPT;
+	*cs++ = MI_NOOP;
 
 	rq->tail = intel_ring_offset(rq, cs);
 	assert_ring_tail_valid(rq->ring, rq->tail);
 }
-static const int gen7_xcs_emit_breadcrumb_sz = 10 + GEN7_XCS_WA * 3;
+static const int gen7_xcs_emit_breadcrumb_sz = 14 + GEN7_XCS_WA * 3;
 #undef GEN7_XCS_WA
 
 static void set_hwstam(struct intel_engine_cs *engine, u32 mask)
@@ -933,16 +941,21 @@ static void i9xx_emit_breadcrumb(struct i915_request *rq, u32 *cs)
 	*cs++ = I915_GEM_HWS_SEQNO_ADDR;
 	*cs++ = rq->fence.seqno;
 
+	*cs++ = MI_STORE_DWORD_INDEX;
+	*cs++ = I915_GEM_HWS_HANGCHECK_ADDR;
+	*cs++ = intel_engine_next_hangcheck_seqno(rq->engine);
+
 	*cs++ = MI_STORE_DWORD_INDEX;
 	*cs++ = I915_GEM_HWS_INDEX_ADDR;
 	*cs++ = rq->global_seqno;
 
 	*cs++ = MI_USER_INTERRUPT;
+	*cs++ = MI_NOOP;
 
 	rq->tail = intel_ring_offset(rq, cs);
 	assert_ring_tail_valid(rq->ring, rq->tail);
 }
-static const int i9xx_emit_breadcrumb_sz = 8;
+static const int i9xx_emit_breadcrumb_sz = 12;
 
 #define GEN5_WA_STORES 8 /* must be at least 1! */
 static void gen5_emit_breadcrumb(struct i915_request *rq, u32 *cs)
@@ -957,6 +970,10 @@ static void gen5_emit_breadcrumb(struct i915_request *rq, u32 *cs)
 	*cs++ = I915_GEM_HWS_SEQNO_ADDR;
 	*cs++ = rq->fence.seqno;
 
+	*cs++ = MI_STORE_DWORD_INDEX;
+	*cs++ = I915_GEM_HWS_HANGCHECK_ADDR;
+	*cs++ = intel_engine_next_hangcheck_seqno(rq->engine);
+
 	BUILD_BUG_ON(GEN5_WA_STORES < 1);
 	for (i = 0; i < GEN5_WA_STORES; i++) {
 		*cs++ = MI_STORE_DWORD_INDEX;
@@ -965,12 +982,11 @@ static void gen5_emit_breadcrumb(struct i915_request *rq, u32 *cs)
 	}
 
 	*cs++ = MI_USER_INTERRUPT;
-	*cs++ = MI_NOOP;
 
 	rq->tail = intel_ring_offset(rq, cs);
 	assert_ring_tail_valid(rq->ring, rq->tail);
 }
-static const int gen5_emit_breadcrumb_sz = GEN5_WA_STORES * 3 + 6;
+static const int gen5_emit_breadcrumb_sz = GEN5_WA_STORES * 3 + 8;
 #undef GEN5_WA_STORES
 
 static void
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 7eec96cf2a0b..e3ac22181295 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -6,6 +6,7 @@
 
 #include <linux/hashtable.h>
 #include <linux/irq_work.h>
+#include <linux/random.h>
 #include <linux/seqlock.h>
 
 #include "i915_gem_batch_pool.h"
@@ -119,7 +120,8 @@ struct intel_instdone {
 
 struct intel_engine_hangcheck {
 	u64 acthd;
-	u32 seqno;
+	u32 last_seqno;
+	u32 next_seqno;
 	unsigned long action_timestamp;
 	struct intel_instdone instdone;
 };
@@ -707,6 +709,8 @@ intel_write_status_page(struct intel_engine_cs *engine, int reg, u32 value)
 #define I915_GEM_HWS_INDEX_ADDR (I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
 #define I915_GEM_HWS_PREEMPT_INDEX	0x32
 #define I915_GEM_HWS_PREEMPT_ADDR (I915_GEM_HWS_PREEMPT_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
+#define I915_GEM_HWS_HANGCHECK		0x34
+#define I915_GEM_HWS_HANGCHECK_ADDR (I915_GEM_HWS_HANGCHECK << MI_STORE_DWORD_INDEX_SHIFT)
 #define I915_GEM_HWS_SEQNO		0x40
 #define I915_GEM_HWS_SEQNO_ADDR (I915_GEM_HWS_SEQNO << MI_STORE_DWORD_INDEX_SHIFT)
 #define I915_GEM_HWS_SCRATCH_INDEX	0x80
@@ -1058,4 +1062,17 @@ static inline bool inject_preempt_hang(struct intel_engine_execlists *execlists)
 
 #endif
 
+static inline u32 intel_engine_next_hangcheck_seqno(struct intel_engine_cs *engine)
+{
+	engine->hangcheck.next_seqno =
+		next_pseudo_random32(engine->hangcheck.next_seqno);
+
+	return engine->hangcheck.next_seqno;
+}
+
+static inline u32 intel_engine_get_hangcheck_seqno(struct intel_engine_cs *engine)
+{
+	return intel_read_status_page(engine, I915_GEM_HWS_HANGCHECK);
+}
+
 #endif /* _INTEL_RINGBUFFER_H_ */
-- 
2.20.1

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