util: Remove RandAddSeedPerfmon

RegQueryValueExA(HKEY_PERFORMANCE_DATA, ...) sometimes hangs bitcoind.exe on Windows during startup, at least on CI.

We have other sources of entropy to seed randomness with on Windows, so should be alright removing this. Might resurrect if less drastic fix is found.

Author: hodlinator

src/random.cpp

@@ -599,7 +599,7 @@ void SeedPeriodic(CSHA512& hasher, RNGState& rng) noexcept
     // Add the events hasher into the mix
     rng.SeedEvents(hasher);
 
-    // Dynamic environment data (performance monitoring, ...)
+    // Dynamic environment data (clocks, resource usage, ...)
     auto old_size = hasher.Size();
     RandAddDynamicEnv(hasher);
     LogDebug(BCLog::RAND, "Feeding %i bytes of dynamic environment data into RNG\n", hasher.Size() - old_size);
@@ -616,7 +616,7 @@ void SeedStartup(CSHA512& hasher, RNGState& rng) noexcept
     // Everything that the 'slow' seeder includes.
     SeedSlow(hasher, rng);
 
-    // Dynamic environment data (performance monitoring, ...)
+    // Dynamic environment data (clocks, resource usage, ...)
     auto old_size = hasher.Size();
     RandAddDynamicEnv(hasher);
 

src/random.h

@@ -49,7 +49,7 @@
  *
  * - RandAddPeriodic() seeds everything that fast seeding includes, but additionally:
  *   - A high-precision timestamp
- *   - Dynamic environment data (performance monitoring, ...)
+ *   - Dynamic environment data (clocks, resource usage, ...)
  *   - Strengthen the entropy for 10 ms using repeated SHA512.
  *   This is run once every minute.
  *

src/randomenv.cpp

@@ -28,7 +28,6 @@
 
 #ifdef WIN32
 #include <windows.h>
-#include <winreg.h>
 #else
 #include <fcntl.h>
 #include <netinet/in.h>
@@ -64,45 +63,6 @@ extern char** environ; // NOLINT(readability-redundant-declaration): Necessary o
 
 namespace {
 
-void RandAddSeedPerfmon(CSHA512& hasher)
-{
-#ifdef WIN32
-    // Seed with the entire set of perfmon data
-
-    // This can take up to 2 seconds, so only do it every 10 minutes.
-    // Initialize last_perfmon to 0 seconds, we don't skip the first call.
-    static std::atomic<SteadyClock::time_point> last_perfmon{SteadyClock::time_point{0s}};
-    auto last_time = last_perfmon.load();
-    auto current_time = SteadyClock::now();
-    if (current_time < last_time + 10min) return;
-    last_perfmon = current_time;
-
-    std::vector<unsigned char> vData(250000, 0);
-    long ret = 0;
-    unsigned long nSize = 0;
-    const size_t nMaxSize = 10000000; // Bail out at more than 10MB of performance data
-    while (true) {
-        nSize = vData.size();
-        ret = RegQueryValueExA(HKEY_PERFORMANCE_DATA, "Global", nullptr, nullptr, vData.data(), &nSize);
-        if (ret != ERROR_MORE_DATA || vData.size() >= nMaxSize)
-            break;
-        vData.resize(std::min((vData.size() * 3) / 2, nMaxSize)); // Grow size of buffer exponentially
-    }
-    RegCloseKey(HKEY_PERFORMANCE_DATA);
-    if (ret == ERROR_SUCCESS) {
-        hasher.Write(vData.data(), nSize);
-        memory_cleanse(vData.data(), nSize);
-    } else {
-        // Performance data is only a best-effort attempt at improving the
-        // situation when the OS randomness (and other sources) aren't
-        // adequate. As a result, failure to read it is isn't considered critical,
-        // so we don't call RandFailure().
-        // TODO: Add logging when the logger is made functional before global
-        // constructors have been invoked.
-    }
-#endif
-}
-
 /** Helper to easily feed data into a CSHA512.
  *
  * Note that this does not serialize the passed object (like stream.h's << operators do).
@@ -227,8 +187,6 @@ void AddAllCPUID(CSHA512& hasher)
 
 void RandAddDynamicEnv(CSHA512& hasher)
 {
-    RandAddSeedPerfmon(hasher);
-
     // Various clocks
 #ifdef WIN32
     FILETIME ftime;