return cache stat instead miss rate for ghost kv cache API

include/gcache/ghost_kv_cache.h

@@ -64,22 +64,21 @@ class SampledGhostKvCache {
 
   void reset_stat() { ghost_cache.reset_stat(); }
 
-  [[nodiscard]] const std::vector<
-      std::tuple</*count*/ uint32_t, /*size*/ uint32_t, /*miss_rate*/ double>>
-  get_miss_rate_curve() const {
-    std::vector<std::tuple<uint32_t, uint32_t, double>> mrc;
+  [[nodiscard]] const std::vector<std::tuple<
+      /*count*/ uint32_t, /*size*/ uint32_t, /*miss_rate*/ CacheStat>>
+  get_cache_stat_curve() const {
+    std::vector<std::tuple<uint32_t, uint32_t, CacheStat>> curve;
     uint32_t curr_count = 0;
     uint32_t curr_size = 0;
     ghost_cache.unsafe_for_each_mru([&](Handle_t h) {
       curr_size += h->kv_size;
       ++curr_count;
       if ((curr_count - ghost_cache.min_size) % ghost_cache.tick == 0) {
-        mrc.emplace_back(
-            curr_count << SampleShift, curr_size << SampleShift,
-            ghost_cache.get_stat_shifted(curr_count).get_miss_rate());
+        curve.emplace_back(curr_count << SampleShift, curr_size << SampleShift,
+                           ghost_cache.get_stat_shifted(curr_count));
       }
     });
-    return mrc;
+    return curve;
     // should be implicitly moved by compiler
     // avoid explict move for Return Value Optimization (RVO)
   }

tests/test_ghost_kv.cpp

@@ -61,20 +61,20 @@ void bench1() {
             << "-------------------------------------------------------------"
             << "-----------------------\n";
 
-  auto mrc = sampled_ghost_kv_cache.get_miss_rate_curve();
+  auto curve = sampled_ghost_kv_cache.get_cache_stat_curve();
   for (uint32_t s = tick; s <= bench_size; s += tick) {
     std::cout << std::setw(5) << s / 1024 << "K|";
     ghost_cache.get_stat(s).print(std::cout, 8);
     std::cout << '|';
     sampled_ghost_kv_cache.get_stat(s).print(std::cout, 8);
     std::cout << '|';
-    auto [count, size, miss_rate] = mrc[s / tick - 1];
+    auto [count, size, cache_stat] = curve[s / tick - 1];
     assert(count == s);
-    if (miss_rate == std::numeric_limits<double>::infinity()) {
+    if (cache_stat.hit_cnt == 0) {
       std::cout << "  NAN";
     } else {
       std::cout << std::setw(5) << std::fixed << std::setprecision(1)
-                << (1 - miss_rate) * 100 << '%';
+                << cache_stat.get_hit_rate() * 100 << '%';
     }
     std::cout << " @" << std::setw(7) << std::fixed << size / 1024 / 1024 << 'M'
               << std::setw(5) << std::fixed << size / count << std::endl;