[PATCH v2 1/2] perf jevents: Add IOMMU metrics for AMD

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

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

These metrics are supported on Zen 2 and newer processors (Rome, Milan,
Genoa, Turin) and are implemented using the standard `amd_iommu` PMU
events. The implementation uses the existing `_zen_model` helper to
ensure these are only generated for Zen 2+. Note that the pde events on
AMD cover both 2M and 1G pages, so 1G pages are implicitly included in
the total hits/misses metrics (sum of pte and pde events).

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.
- 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/amd_metrics.py | 57 ++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/tools/perf/pmu-events/amd_metrics.py b/tools/perf/pmu-events/amd_metrics.py
index 971f6e7af1f8..dccfcacaf148 100755
--- a/tools/perf/pmu-events/amd_metrics.py
+++ b/tools/perf/pmu-events/amd_metrics.py
@@ -265,6 +265,62 @@ def AmdDtlb() -> Optional[MetricGroup]:
     ], description="Data TLB metrics")
 
 
+def AmdIotlb() -> Optional[MetricGroup]:
+    global _zen_model
+    if _zen_model < 2:
+        return None
+
+    # On AMD, the pde events cover both 2M and 1G pages.
+    total_hit = Event("amd_iommu/mem_iommu_tlb_pte_hit/") + Event(
+        "amd_iommu/mem_iommu_tlb_pde_hit/"
+    )
+    total_miss = Event("amd_iommu/mem_iommu_tlb_pte_mis/") + Event(
+        "amd_iommu/mem_iommu_tlb_pde_mis/"
+    )
+    miss_rate = d_ratio(total_miss, total_miss + total_hit)
+
+    interrupt_cache_hit = Event("amd_iommu/int_dte_hit/")
+    interrupt_cache_miss = Event("amd_iommu/int_dte_mis/")
+    interrupt_cache_lookup = interrupt_cache_hit + interrupt_cache_miss
+    interrupt_cache_miss_rate = d_ratio(
+        interrupt_cache_miss, interrupt_cache_miss + interrupt_cache_hit
+    )
+
+    return MetricGroup(
+        "iotlb",
+        [
+            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%"),
+            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%",
+            ),
+        ],
+        description="IOMMU TLB metrics",
+    )
+
+
 def AmdItlb():
     global _zen_model
     l2h = Event("bp_l1_tlb_miss_l2_tlb_hit", "bp_l1_tlb_miss_l2_hit")
@@ -473,6 +529,7 @@ def main() -> None:
         AmdBr(),
         AmdCtxSw(),
         AmdDtlb(),
+        AmdIotlb(),
         AmdItlb(),
         AmdLdSt(),
         AmdUpc(),
-- 
2.54.0.823.g6e5bcc1fc9-goog