From a22d4e1061eeb69484025208ec2198ab32b31368 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= <maze@google.com>
Date: Sat, 13 Sep 2025 03:21:47 -0700
Subject: [PATCH] BpfNetworkStats: use `atomic` for ifindex cache when possible
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Test: TreeHugger
Flag: EXEMPT BUGFIX
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ibc24f079711c36a8bc6ff850fc5b07fb6546b3ae
---
 .../libs/libnetworkstats/BpfNetworkStats.cpp  | 29 ++++++++++++++-----
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/service-t/native/libs/libnetworkstats/BpfNetworkStats.cpp b/service-t/native/libs/libnetworkstats/BpfNetworkStats.cpp
index da01ed6400..ae8dbbe321 100644
--- a/service-t/native/libs/libnetworkstats/BpfNetworkStats.cpp
+++ b/service-t/native/libs/libnetworkstats/BpfNetworkStats.cpp
@@ -50,23 +50,38 @@ const BpfMapRO<uint32_t, StatsValue>& getIfaceStatsMap() {
     return ifaceStatsMap;
 }
 
-#ifndef __riscv
-#ifndef __ILP32__
+static constexpr unsigned cacheSize = 1024;  // see 'iface_index_name_map' bpf map size
+
+#if !defined(__ILP32__) && !defined(__riscv)
 static_assert(std::atomic<IfaceValue>::is_always_lock_free,
               "Error: 16-byte IfaceValue is not lock-free on this platform!");
-#endif
+#define CACHE_IS_ATOMIC
+static std::atomic<IfaceValue> cache[cacheSize];
+#else
+static IfaceValue cache[cacheSize];
 #endif
 
-static constexpr unsigned cacheSize = 1024;  // see 'iface_index_name_map' bpf map size
-static IfaceValue cache[cacheSize];
 
 static inline const IfaceValue& updateCache(unsigned i, const IfaceValue &v) {
-    if (i < cacheSize) cache[i] = v;
+    if (i < cacheSize) {
+#ifdef CACHE_IS_ATOMIC
+        cache[i].store(v, std::memory_order_relaxed);
+#else
+        cache[i] = v;
+#endif
+    }
     return v;
 }
 
 Result<IfaceValue> ifindex2name(const uint32_t ifindex) {
-    if (ifindex < cacheSize && cache[ifindex].name[0]) return cache[ifindex];
+    if (ifindex < cacheSize) {
+#ifdef CACHE_IS_ATOMIC
+        IfaceValue c = cache[ifindex].load(std::memory_order_relaxed);
+#else
+        IfaceValue c = cache[ifindex];
+#endif
+        if (c.name[0]) return c;
+    }
 
     Result<IfaceValue> v = getIfaceIndexNameMap().readValue(ifindex);
     if (v.ok()) return updateCache(ifindex, v.value());