planner: add info logging around migration opportunities

include/faabric/batch-scheduler/SchedulingDecision.h

@@ -101,7 +101,7 @@ class SchedulingDecision
 
     std::set<std::string> uniqueHosts();
 
-    void print();
+    void print(const std::string& logLevel = "debug");
 };
 
 }

src/batch-scheduler/SchedulingDecision.cpp

@@ -59,21 +59,35 @@ std::set<std::string> SchedulingDecision::uniqueHosts()
     return std::set<std::string>(hosts.begin(), hosts.end());
 }
 
-void SchedulingDecision::print()
+void SchedulingDecision::print(const std::string& logLevel)
 {
-    SPDLOG_DEBUG("-------------- Decision for App: {} ----------------", appId);
-    SPDLOG_DEBUG("MsgId\tAppId\tGroupId\tGrIdx\tHostIp");
+    std::string printedText;
+    printedText += fmt::format(
+      "-------------- Decision for App: {} ----------------\n", appId);
+    printedText += "MsgId\tAppId\tGroupId\tGrIdx\tHostIp\n";
     // Modulo a big number so that we can get the UUIDs to fit within one tab
     int formatBase = 1e6;
     for (int i = 0; i < hosts.size(); i++) {
-        SPDLOG_DEBUG("{}\t{}\t{}\t{}\t{}",
-                     messageIds.at(i) % formatBase,
-                     appId % formatBase,
-                     groupId % formatBase,
-                     groupIdxs.at(i),
-                     hosts.at(i));
+        printedText += fmt::format("{}\t{}\t{}\t{}\t{}\n",
+                                   messageIds.at(i) % formatBase,
+                                   appId % formatBase,
+                                   groupId % formatBase,
+                                   groupIdxs.at(i),
+                                   hosts.at(i));
+    }
+    printedText += fmt::format(
+      "------------- End Decision for App {} ---------------", appId);
+
+    if (logLevel == "debug") {
+        SPDLOG_DEBUG(printedText);
+    } else if (logLevel == "info") {
+        SPDLOG_INFO(printedText);
+    } else if (logLevel == "warn") {
+        SPDLOG_WARN(printedText);
+    } else if (logLevel == "error") {
+        SPDLOG_ERROR(printedText);
+    } else {
+        SPDLOG_ERROR("Unrecognised log level: {}", logLevel);
     }
-    SPDLOG_DEBUG("------------- End Decision for App {} ---------------",
-                 appId);
 }
 }

src/planner/Planner.cpp

@@ -404,6 +404,7 @@ Planner::callBatch(std::shared_ptr<BatchExecuteRequest> req)
     // on the old decision (we don't care the one we send), so we make sure
     // we are scheduling the same messages from the old request
     if (decisionType == faabric::batch_scheduler::DecisionType::DIST_CHANGE) {
+        SPDLOG_INFO("App {} asked for migration opportunities");
         auto oldReq = state.inFlightReqs.at(appId).first;
         req->clear_messages();
         for (const auto& msg : oldReq->messages()) {
@@ -425,7 +426,7 @@ Planner::callBatch(std::shared_ptr<BatchExecuteRequest> req)
     }
 
     if (*decision == DO_NOT_MIGRATE_DECISION) {
-        SPDLOG_DEBUG("Decided to not migrate app: {}", appId);
+        SPDLOG_INFO("Decided to not migrate app: {}", appId);
         return decision;
     }
 
@@ -493,14 +494,17 @@ Planner::callBatch(std::shared_ptr<BatchExecuteRequest> req)
             break;
         }
         case faabric::batch_scheduler::DecisionType::DIST_CHANGE: {
-            // 0. Log the decision in debug mode
-#ifndef NDEBUG
-            decision->print();
-#endif
-
             auto oldReq = state.inFlightReqs.at(appId).first;
             auto oldDec = state.inFlightReqs.at(appId).second;
 
+            // 0. For the time being, when migrating we always print both
+            // decisions (old and new)
+            SPDLOG_INFO("Decided to migrate app {}!", appId);
+            SPDLOG_INFO("Old decision:");
+            oldDec->print("info");
+            SPDLOG_INFO("New decision:");
+            decision->print("info");
+
             // We want to let all hosts involved in the migration (not only
             // those in the new decision) that we are gonna migrate. For the
             // evicted hosts (those present in the old decision but not in the