From 159f2eef748c2d498bbccff7539c2a39dcda420d Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Fri, 16 Aug 2024 15:35:35 -0700
Subject: [PATCH] Use group leader fd

Events in the same group should be associated with the same set of
instructions
---
 ServerBench.cpp | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/ServerBench.cpp b/ServerBench.cpp
index 49cf546..891f9f6 100644
--- a/ServerBench.cpp
+++ b/ServerBench.cpp
@@ -171,7 +171,8 @@ double toSeconds(timeval t) {
 #ifdef __linux__
 #include <linux/perf_event.h>
 struct PerfCounter {
-  PerfCounter(int type, int config, const std::string &labels = {})
+  PerfCounter(int type, int config, const std::string &labels = {},
+              int groupLeaderFd = -1)
       : labels(labels) {
     struct perf_event_attr pe;
 
@@ -183,7 +184,7 @@ struct PerfCounter {
     pe.exclude_kernel = 1;
     pe.exclude_hv = 1;
 
-    fd = perf_event_open(&pe, 0, -1, -1, 0);
+    fd = perf_event_open(&pe, 0, -1, groupLeaderFd, 0);
     if (fd < 0 && errno != ENOENT && errno != EINVAL) {
       perror(labels.c_str());
     }
@@ -214,6 +215,7 @@ struct PerfCounter {
 
   bool ok() const { return fd >= 0; }
   const std::string &getLabels() const { return labels; }
+  int getFd() const { return fd; }
 
 private:
   int fd;
@@ -246,7 +248,8 @@ int main(int argc, char **argv) {
     cs.getMetricsV1(&metrics, &metricsCount);
 
     PerfCounter instructions{PERF_TYPE_HARDWARE, PERF_COUNT_HW_INSTRUCTIONS};
-    PerfCounter cycles{PERF_TYPE_HARDWARE, PERF_COUNT_HW_CPU_CYCLES};
+    PerfCounter cycles{PERF_TYPE_HARDWARE, PERF_COUNT_HW_CPU_CYCLES, "",
+                       instructions.getFd()};
 
     std::vector<PerfCounter> cacheCounters;
     for (auto [id, idStr] : std::initializer_list<std::pair<int, std::string>>{
@@ -265,6 +268,7 @@ int main(int argc, char **argv) {
                {PERF_COUNT_HW_CACHE_OP_WRITE, "write"},
                {PERF_COUNT_HW_CACHE_OP_PREFETCH, "prefetch"},
            }) {
+        int groupLeaderFd = -1;
         for (auto [result, resultStr] :
              std::initializer_list<std::pair<int, std::string>>{
                  {PERF_COUNT_HW_CACHE_RESULT_MISS, "miss"},
@@ -273,9 +277,14 @@ int main(int argc, char **argv) {
           auto labels = "{id=\"" + idStr + "\", op=\"" + opStr +
                         "\", result=\"" + resultStr + "\"}";
           cacheCounters.emplace_back(PERF_TYPE_HW_CACHE,
-                                     id | (op << 8) | (result << 16), labels);
+                                     id | (op << 8) | (result << 16), labels,
+                                     groupLeaderFd);
           if (!cacheCounters.back().ok()) {
             cacheCounters.pop_back();
+          } else {
+            if (groupLeaderFd == -1) {
+              groupLeaderFd = cacheCounters.back().getFd();
+            }
           }
         }
       }