[PATCH v2 2/2] perf jevents: Add IOMMU metrics for Intel

[Chun-Tse Shao <ctshao@google.com>]

Add IOMMU Translation Lookaside Buffer (TLB) and interrupt cache metrics
to perf jevents for Intel platforms. This enhances I/O performance
observability, allowing fleet-wide monitoring of IOMMU overhead.

These metrics are supported on platforms that expose the required uncore
IIO IOMMU events (such as Emerald Rapids and Granite Rapids). The Intel
implementation dynamically detects event availability at generation time.
It requires at least the TLB events to expose the metric group, while the
interrupt cache events are optional. This allows platforms like Emerald
Rapids, which lack IOMMU interrupt cache events, to still expose the
IOMMU TLB metrics.

The following metrics are added:
- iotlb_total_hit: Total IOTLB hits (4K, 2M, 1G pages).
- iotlb_total_miss: Total IOTLB misses.
- iotlb_miss_rate: IOTLB miss rate.
- iotlb_interrupt_cache_hit: Interrupt cache hits.
- iotlb_interrupt_cache_miss: Interrupt cache misses (calculated as
  lookup - hit, clamped to zero).
- iotlb_interrupt_cache_lookup: Interrupt cache lookups.
- iotlb_interrupt_cache_miss_rate: Interrupt cache miss rate.

Tested:
  # perf stat -M \
    iotlb_total_hit,iotlb_total_miss,iotlb_miss_rate \
    --per-socket --metric-only -a -j -- sleep 10
  {"socket" : "S0", "counters" : 10,
   "hits  iotlb_total_hit" : "3579249.0",
   "%  iotlb_miss_rate" : "0.0",
   "misses  iotlb_total_miss" : "3.0"}
  {"socket" : "S1", "counters" : 10,
   "hits  iotlb_total_hit" : "0.0",
   "%  iotlb_miss_rate" : "0.0",
   "misses  iotlb_total_miss" : "0.0"}

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
Assisted-by: Gemini:gemini-3.1-pro-preview
---
 tools/perf/pmu-events/intel_metrics.py | 62 ++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/tools/perf/pmu-events/intel_metrics.py b/tools/perf/pmu-events/intel_metrics.py
index 52035433b505..c3a5c2965f74 100755
--- a/tools/perf/pmu-events/intel_metrics.py
+++ b/tools/perf/pmu-events/intel_metrics.py
@@ -457,6 +457,67 @@ def IntelIlp() -> MetricGroup:
     ])
 
 
+def IntelIotlb() -> Optional[MetricGroup]:
+  try:
+    total_hit = (
+        Event("UNC_IIO_IOMMU0.4K_HITS")
+        + Event("UNC_IIO_IOMMU0.2M_HITS")
+        + Event("UNC_IIO_IOMMU0.1G_HITS")
+    )
+    total_miss = Event("UNC_IIO_IOMMU0.MISSES")
+  except:
+    return None
+
+  miss_rate = d_ratio(total_miss, total_miss + total_hit)
+  metrics = [
+      Metric("iotlb_total_hit", "IOTLB total hit", total_hit, "hits"),
+      Metric("iotlb_total_miss", "IOTLB total miss", total_miss, "misses"),
+      Metric("iotlb_miss_rate", "IOTLB miss rate", miss_rate, "100%"),
+  ]
+
+  try:
+    interrupt_cache_hit = Event("UNC_IIO_IOMMU3.INT_CACHE_HITS")
+    interrupt_cache_lookup = Event("UNC_IIO_IOMMU3.INT_CACHE_LOOKUPS")
+    interrupt_cache_miss = max(interrupt_cache_lookup - interrupt_cache_hit, 0)
+    interrupt_cache_miss_rate = d_ratio(
+        interrupt_cache_miss, interrupt_cache_miss + interrupt_cache_hit
+    )
+    metrics += [
+        Metric(
+            "iotlb_interrupt_cache_hit",
+            "IOTLB interrupt cache hit",
+            interrupt_cache_hit,
+            "hits",
+        ),
+        Metric(
+            "iotlb_interrupt_cache_miss",
+            "IOTLB interrupt cache miss",
+            interrupt_cache_miss,
+            "misses",
+        ),
+        Metric(
+            "iotlb_interrupt_cache_lookup",
+            "IOTLB interrupt cache lookup",
+            interrupt_cache_lookup,
+            "lookups",
+        ),
+        Metric(
+            "iotlb_interrupt_cache_miss_rate",
+            "IOTLB interrupt cache miss rate",
+            interrupt_cache_miss_rate,
+            "100%",
+        ),
+    ]
+  except:
+    pass
+
+  return MetricGroup(
+      "iotlb",
+      metrics,
+      description="IOMMU TLB metrics",
+  )
+
+
 def IntelL2() -> Optional[MetricGroup]:
     try:
         DC_HIT = Event("L2_RQSTS.DEMAND_DATA_RD_HIT")
@@ -1105,6 +1166,7 @@ def main() -> None:
         IntelCtxSw(),
         IntelFpu(),
         IntelIlp(),
+        IntelIotlb(),
         IntelL2(),
         IntelLdSt(),
         IntelMissLat(),
-- 
2.54.0.823.g6e5bcc1fc9-goog