drm/i915: Decouple hang detection from hangcheck period

Hangcheck state accumulation has gained more steps
along the years, like head movement and more recently the
subunit inactivity check. As the subunit sampling is only
done if the previous state check showed inactivity, we
have added more stages (and time) to reach a hang verdict.

Asymmetric engine states led to different actual weight of
'one hangcheck unit' and it was demonstrated in some
hangs that due to difference in stages, simpler engines
were accused falsely of a hang as their scoring was much
more quicker to accumulate above the hang treshold.

To completely decouple the hangcheck guilty score
from the hangcheck period, convert hangcheck score to a
rough period of inactivity measurement. As these are
tracked as jiffies, they are meaningful also across
reset boundaries. This makes finding a guilty engine
more accurate across multi engine activity scenarios,
especially across asymmetric engines.

We lose the ability to detect cross batch malicious attempts
to hinder the progress. Plan is to move this functionality
to be part of context banning which is more natural fit,
later in the series.

v2: use time_before macros (Chris)
    reinstate the pardoning of moving engine after hc (Chris)
v3: avoid global state for per engine stall detection (Chris)
v4: take timeline last retirement into account (Chris)
v5: do debug print on pardoning, split out retirement timestamp (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>

1 files changed, 12 insertions, 34 deletions

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 4bcf1a0f5675..d5a4ec9b507f 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -316,28 +316,6 @@ static void print_error_buffers(struct drm_i915_error_state_buf *m,
 	}
 }
 
-static const char *hangcheck_action_to_str(enum intel_engine_hangcheck_action a)
-{
-	switch (a) {
-	case HANGCHECK_IDLE:
-		return "idle";
-	case HANGCHECK_WAIT:
-		return "wait";
-	case HANGCHECK_ACTIVE_SEQNO:
-		return "active seqno";
-	case HANGCHECK_ACTIVE_HEAD:
-		return "active head";
-	case HANGCHECK_ACTIVE_SUBUNITS:
-		return "active subunits";
-	case HANGCHECK_KICK:
-		return "kick";
-	case HANGCHECK_HUNG:
-		return "hung";
-	}
-
-	return "unknown";
-}
-
 static void error_print_instdone(struct drm_i915_error_state_buf *m,
 				 struct drm_i915_error_engine *ee)
 {
@@ -445,9 +423,13 @@ static void error_print_engine(struct drm_i915_error_state_buf *m,
 	err_printf(m, "  waiting: %s\n", yesno(ee->waiting));
 	err_printf(m, "  ring->head: 0x%08x\n", ee->cpu_ring_head);
 	err_printf(m, "  ring->tail: 0x%08x\n", ee->cpu_ring_tail);
-	err_printf(m, "  hangcheck: %s [%d]\n",
-		   hangcheck_action_to_str(ee->hangcheck_action),
-		   ee->hangcheck_score);
+	err_printf(m, "  hangcheck stall: %s\n", yesno(ee->hangcheck_stalled));
+	err_printf(m, "  hangcheck action: %s\n",
+		   hangcheck_action_to_str(ee->hangcheck_action));
+	err_printf(m, "  hangcheck action timestamp: %lu, %u ms ago\n",
+		   ee->hangcheck_timestamp,
+		   jiffies_to_msecs(jiffies - ee->hangcheck_timestamp));
+
 	error_print_request(m, "  ELSP[0]: ", &ee->execlist[0]);
 	error_print_request(m, "  ELSP[1]: ", &ee->execlist[1]);
 }
@@ -536,7 +518,6 @@ int i915_error_state_to_str(struct drm_i915_error_state_buf *m,
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 	struct drm_i915_error_state *error = error_priv->error;
 	struct drm_i915_error_object *obj;
-	int max_hangcheck_score;
 	int i, j;
 
 	if (!error) {
@@ -553,13 +534,9 @@ int i915_error_state_to_str(struct drm_i915_error_state_buf *m,
 	err_printf(m, "Uptime: %ld s %ld us\n",
 		   error->uptime.tv_sec, error->uptime.tv_usec);
 	err_print_capabilities(m, &error->device_info);
-	max_hangcheck_score = 0;
-	for (i = 0; i < ARRAY_SIZE(error->engine); i++) {
-		if (error->engine[i].hangcheck_score > max_hangcheck_score)
-			max_hangcheck_score = error->engine[i].hangcheck_score;
-	}
+
 	for (i = 0; i < ARRAY_SIZE(error->engine); i++) {
-		if (error->engine[i].hangcheck_score == max_hangcheck_score &&
+		if (error->engine[i].hangcheck_stalled &&
 		    error->engine[i].pid != -1) {
 			err_printf(m, "Active process (on ring %s): %s [%d]\n",
 				   engine_str(i),
@@ -945,7 +922,7 @@ static uint32_t i915_error_generate_code(struct drm_i915_private *dev_priv,
 	 * strictly a client bug. Use instdone to differentiate those some.
 	 */
 	for (i = 0; i < I915_NUM_ENGINES; i++) {
-		if (error->engine[i].hangcheck_action == HANGCHECK_HUNG) {
+		if (error->engine[i].hangcheck_stalled) {
 			if (engine_id)
 				*engine_id = i;
 
@@ -1163,8 +1140,9 @@ static void error_record_engine_registers(struct drm_i915_error_state *error,
 		ee->hws = I915_READ(mmio);
 	}
 
-	ee->hangcheck_score = engine->hangcheck.score;
+	ee->hangcheck_timestamp = engine->hangcheck.action_timestamp;
 	ee->hangcheck_action = engine->hangcheck.action;
+	ee->hangcheck_stalled = engine->hangcheck.stalled;
 
 	if (USES_PPGTT(dev_priv)) {
 		int i;