Merge bitcoin/bitcoin#33517: multiprocess: Fix high overhead from message logging

0626b90 multiprocess: align our logging with libmultiprocess's (Cory Fields)
9d06822 multiprocess: update multiprocess EventLoop construction to use options (Cory Fields)

Pull request description:

  This fixes bitcoin-core/libmultiprocess#215 on Core's side. ~It depends on bitcoin-core/libmultiprocess#220 being merged upstream, and a PR to update our subtree. I've included a subtree merge from my repo here for now, but will rebase on top of the merge from upstream once it's in.~ Edit: Rebased on top of #33518.

  For context: before bitcoin-core/libmultiprocess#220, libmultiprocess serializesd every log message parameter, even if that message was ultimately going to be discarded. The upstream PR accomplished 2 main things:
  - Creates logging categories, similar to Core's
  - Using macros, avoids serializing parameters for disabled log levels.

  That allowed the expensive serialization to be skipped, but the default log level is `Trace`. This PR updates our usage of libmultiprocess options to honor our log categories and levels.

  Because of the substantial unnecessary overhead (see the [flamegraphs](bitcoin-core/libmultiprocess#215). Logging accounts for 50% of my application's cpu time, and nearly 10% of bitcoin-node's, both of which go to ~0% once fixed), it'd be a shame to ship the first multiprocess binaries without this fixed. So I propose that we also backport this (and the required libmultiprocess subtree merge) ~to v30. Sorry about the timing~ :(

  Edit: Didn't make it for v30, but it would still make sense to backport for a v30.1.

ACKs for top commit:
  Sjors:
    ACK 0626b90
  TheCharlatan:
    ACK 0626b90
  sipa:
    utACK 0626b90

Tree-SHA512: 70b63b62d1f6de547f4d4775538d7bcaf32f57d8a72c5b26762b57755810c8be6942d9dfebab43cf1c1d8d025a555f72a48e9ebf3d84f8d40d6592ca801cda5d

Author: glozow

src/ipc/capnp/protocol.cpp

@@ -30,10 +30,36 @@
 namespace ipc {
 namespace capnp {
 namespace {
-void IpcLogFn(bool raise, std::string message)
+
+BCLog::Level ConvertIPCLogLevel(mp::Log level)
+{
+    switch (level) {
+        case mp::Log::Trace: return BCLog::Level::Trace;
+        case mp::Log::Debug: return BCLog::Level::Debug;
+        case mp::Log::Info: return BCLog::Level::Info;
+        case mp::Log::Warning: return BCLog::Level::Warning;
+        case mp::Log::Error: return BCLog::Level::Error;
+        case mp::Log::Raise: return BCLog::Level::Error;
+    } // no default case, so the compiler can warn about missing cases
+
+    // Be conservative and assume that if MP ever adds a new log level, it
+    // should only be shown at our most verbose level.
+    return BCLog::Level::Trace;
+}
+
+mp::Log GetRequestedIPCLogLevel()
+{
+    if (LogAcceptCategory(BCLog::IPC, BCLog::Level::Trace)) return mp::Log::Trace;
+    if (LogAcceptCategory(BCLog::IPC, BCLog::Level::Debug)) return mp::Log::Debug;
+
+    // Info, Warning, and Error are logged unconditionally
+    return mp::Log::Info;
+}
+
+void IpcLogFn(mp::LogMessage message)
 {
-    LogDebug(BCLog::IPC, "%s\n", message);
-    if (raise) throw Exception(message);
+    LogPrintLevel(BCLog::IPC, ConvertIPCLogLevel(message.level), "%s\n", message.message);
+    if (message.level == mp::Log::Raise) throw Exception(message.message);
 }
 
 class CapnpProtocol : public Protocol
@@ -62,7 +88,11 @@ class CapnpProtocol : public Protocol
     {
         assert(!m_loop);
         mp::g_thread_context.thread_name = mp::ThreadName(exe_name);
-        m_loop.emplace(exe_name, &IpcLogFn, &m_context);
+        mp::LogOptions opts = {
+            .log_fn = IpcLogFn,
+            .log_level = GetRequestedIPCLogLevel()
+        };
+        m_loop.emplace(exe_name, std::move(opts), &m_context);
         if (ready_fn) ready_fn();
         mp::ServeStream<messages::Init>(*m_loop, fd, init);
         m_parent_connection = &m_loop->m_incoming_connections.back();
@@ -90,7 +120,11 @@ class CapnpProtocol : public Protocol
         std::promise<void> promise;
         m_loop_thread = std::thread([&] {
             util::ThreadRename("capnp-loop");
-            m_loop.emplace(exe_name, &IpcLogFn, &m_context);
+            mp::LogOptions opts = {
+                .log_fn = IpcLogFn,
+                .log_level = GetRequestedIPCLogLevel()
+            };
+            m_loop.emplace(exe_name, std::move(opts), &m_context);
             m_loop_ref.emplace(*m_loop);
             promise.set_value();
             m_loop->loop();