From 357e095a7be7131c3706164404a896473685ea79 Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Fri, 5 Feb 2021 13:35:59 +0100
Subject: [PATCH] Add some stats for the evaluation caching

---
 src/libexpr/eval.cc | 30 ++++++++++++++++++++++++++++++
 src/libexpr/eval.hh |  6 ++++++
 2 files changed, 36 insertions(+)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 534bdc15a..e63bf3fe1 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1257,6 +1257,27 @@ ValueCache::CacheResult ValueCache::getValue(Store & store, const std::vector<Sy
         cachedValue);
 }
 
+void EvalState::updateCacheStats(ValueCache::CacheResult cacheResult)
+{
+    switch (cacheResult.returnCode) {
+        case ValueCache::CacheHit:
+            nrCacheHits++;
+            break;
+        case ValueCache::CacheMiss:
+            nrCacheMisses++;
+            break;
+        case ValueCache::UnCacheable:
+            nrUncacheable++;
+            break;
+        case ValueCache::NoCacheKey:
+            nrUncached++;
+            break;
+        case ValueCache::Forward:
+            nrCacheHits++;
+            break;
+    };
+}
+
 struct ExprCastedVar : Expr
 {
     Value * v;
@@ -1280,6 +1301,7 @@ EvalState::AttrAccesResult EvalState::lazyGetOptionalAttrField(Value & attrs, co
     Value * dest = allocValue();
     auto evalCache = attrs.getCache();
     auto cacheResult = evalCache.getValue(*store, selector, *dest);
+    updateCacheStats(cacheResult);
 
     if (cacheResult.returnCode == ValueCache::CacheHit) {
         if (cacheResult.lastQueriedSymbolIfMissing)
@@ -1324,6 +1346,7 @@ EvalState::AttrAccesResult EvalState::getOptionalAttrField(Value & attrs, const
         };
 
     auto cacheResult = evalCache.getValue(*store, selector, dest);
+    updateCacheStats(cacheResult);
 
     if (cacheResult.returnCode == ValueCache::CacheHit) {
         if (cacheResult.lastQueriedSymbolIfMissing)
@@ -2306,6 +2329,13 @@ void EvalState::printStats()
         topObj.attr("nrLookups", nrLookups);
         topObj.attr("nrPrimOpCalls", nrPrimOpCalls);
         topObj.attr("nrFunctionCalls", nrFunctionCalls);
+        {
+            auto cache = topObj.object("evalCache");
+            cache.attr("nrCacheMisses", nrCacheMisses);
+            cache.attr("nrCacheHits", nrCacheHits);
+            cache.attr("nrUncached", nrUncached);
+            cache.attr("nrUncacheable", nrUncacheable);
+        }
 #if HAVE_BOEHMGC
         {
             auto gc = topObj.object("gc");
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 4af0ec98d..291e1bf8b 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -342,6 +342,8 @@ public:
 
     void realiseContext(const PathSet & context);
 
+    void updateCacheStats(ValueCache::CacheResult);
+
 private:
 
     unsigned long nrEnvs = 0;
@@ -355,6 +357,10 @@ private:
     unsigned long nrListConcats = 0;
     unsigned long nrPrimOpCalls = 0;
     unsigned long nrFunctionCalls = 0;
+    unsigned long nrCacheHits = 0;
+    unsigned long nrCacheMisses = 0;
+    unsigned long nrUncacheable = 0;
+    unsigned long nrUncached = 0;
 
     bool countCalls;