[PATCH v4 12/12] drm/xe: Track parallel page fault activity in GT stats

[Matthew Brost <matthew.brost@intel.com>]

Add a new GT statistic, PARALLEL_PAGEFAULT_COUNT, to record when
multiple page fault workers are active concurrently.

When a worker dequeues a fault, scan peer workers for an active
cache entry and increment the counter if another fault is already
in flight. This provides basic visibility into parallel fault
handling behavior for performance analysis and tuning.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_gt_stats.c       |  1 +
 drivers/gpu/drm/xe/xe_gt_stats_types.h |  1 +
 drivers/gpu/drm/xe/xe_pagefault.c      | 18 +++++++++++++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_gt_stats.c b/drivers/gpu/drm/xe/xe_gt_stats.c
index cdd467dfb46d..621d1a2df067 100644
--- a/drivers/gpu/drm/xe/xe_gt_stats.c
+++ b/drivers/gpu/drm/xe/xe_gt_stats.c
@@ -58,6 +58,7 @@ static const char *const stat_description[__XE_GT_STATS_NUM_IDS] = {
 	DEF_STAT_STR(CHAIN_IRQ_PAGEFAULT_COUNT, "chain_irq_pagefault_count"),
 	DEF_STAT_STR(CHAIN_DRAIN_IRQ_PAGEFAULT_COUNT, "chain_drain_irq_pagefault_count"),
 	DEF_STAT_STR(CHAIN_MISMATCH_PAGEFAULT_COUNT, "chain_mismatch_pagefault_count"),
+	DEF_STAT_STR(PARALLEL_PAGEFAULT_COUNT, "parallel_pagefault_count"),
 	DEF_STAT_STR(LAST_PAGEFAULT_COUNT, "last_pagefault_count"),
 	DEF_STAT_STR(SVM_PAGEFAULT_COUNT, "svm_pagefault_count"),
 	DEF_STAT_STR(TLB_INVAL, "tlb_inval_count"),
diff --git a/drivers/gpu/drm/xe/xe_gt_stats_types.h b/drivers/gpu/drm/xe/xe_gt_stats_types.h
index 591e614e1cfc..075a12152ae2 100644
--- a/drivers/gpu/drm/xe/xe_gt_stats_types.h
+++ b/drivers/gpu/drm/xe/xe_gt_stats_types.h
@@ -13,6 +13,7 @@ enum xe_gt_stats_id {
 	XE_GT_STATS_ID_CHAIN_IRQ_PAGEFAULT_COUNT,
 	XE_GT_STATS_ID_CHAIN_DRAIN_IRQ_PAGEFAULT_COUNT,
 	XE_GT_STATS_ID_CHAIN_MISMATCH_PAGEFAULT_COUNT,
+	XE_GT_STATS_ID_PARALLEL_PAGEFAULT_COUNT,
 	XE_GT_STATS_ID_LAST_PAGEFAULT_COUNT,
 	XE_GT_STATS_ID_SVM_PAGEFAULT_COUNT,
 	XE_GT_STATS_ID_TLB_INVAL,
diff --git a/drivers/gpu/drm/xe/xe_pagefault.c b/drivers/gpu/drm/xe/xe_pagefault.c
index d252a8c9d88c..2a37a4c97aad 100644
--- a/drivers/gpu/drm/xe/xe_pagefault.c
+++ b/drivers/gpu/drm/xe/xe_pagefault.c
@@ -458,9 +458,10 @@ static bool xe_pagefault_queue_pop(struct xe_pagefault_queue *pf_queue,
 {
 	struct xe_device *xe = container_of(pf_queue, typeof(*xe),
 					    usm.pf_queue);
-	struct xe_pagefault_work *pf_work;
+	struct xe_pagefault_work *pf_work, *__pf_work;
 	struct xe_pagefault *lpf;
 	size_t align = SZ_2M;
+	int i;
 
 	guard(spinlock_irq)(&pf_queue->lock);
 
@@ -497,6 +498,21 @@ static bool xe_pagefault_queue_pop(struct xe_pagefault_queue *pf_queue,
 	pf_work->cache.pf = lpf;
 	lpf->consumer.alloc_state = XE_PAGEFAULT_ALLOC_STATE_ACTIVE;
 
+	for (i = 0, __pf_work = xe->usm.pf_workers;
+	     i < xe->info.num_pf_work; ++i, ++__pf_work) {
+		u64 cache_start = __pf_work->cache.start;
+
+		if (__pf_work == pf_work)
+			continue;
+
+		if (cache_start != XE_PAGEFAULT_CACHE_START_INVALID) {
+			xe_gt_stats_incr(xe_root_mmio_gt(xe),
+					 XE_GT_STATS_ID_PARALLEL_PAGEFAULT_COUNT,
+					 1);
+			break;
+		}
+	}
+
 	/* Drain queue until empty or new fault found */
 	while (1) {
 		if (pf_queue->tail == pf_queue->head)
-- 
2.34.1