MSR plugin update:

-check if counters already enabled before programming them
-reset counters if stopped

src/sensors/msr/MSRSensorGroup.cpp

@@ -16,6 +16,7 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <bitset>
 #include <atomic>
 #include <exception>
 #include <utility>
@@ -42,6 +43,11 @@ void MSRSensorGroup::start() {
 		return;
 	}
 
+	if (!program_fixed()) {
+        LOG(error) << "MSR fixed counters already in use! Can not start counters";
+        return;
+    }
+
 	for (auto &kv : cpuToFd) {
 		int cpu = kv.first;
 		char * path = new char[200];
@@ -60,8 +66,6 @@ void MSRSensorGroup::start() {
 		cpuToFd[cpu] = handle;
 	}
 
-	program_fixed();
-
 	_keepRunning = 1;
 	_pendingTasks++;
 	_timer->async_wait(std::bind(&MSRSensorGroup::readAsync, this));
@@ -69,13 +73,30 @@ void MSRSensorGroup::start() {
 }
 
 void MSRSensorGroup::stop() {
+    int temp = _keepRunning;
+
 	_keepRunning = 0;
 	
-	for (auto &kv: cpuToFd) {
-		close(kv.second);
-		kv.second = -1;
-	}
-	 
+	//only close this stuff if we have been properly started before
+    if (temp) {
+        //close file descriptors
+        for (auto &kv: cpuToFd) {
+            close(kv.second);
+            kv.second = -1;
+        }
+
+        //reset counters
+        for (auto& kv : cpuToFd) {
+            //disable counters before writing anything else
+            msr_write(IA32_CR_PERF_GLOBAL_CTRL, 0, kv.first);
+            //reset all bits to 0
+            msr_write(IA32_CR_FIXED_CTR_CTRL, 0, kv.first);
+            //set all global enable bits to 1
+            uint64_t value = (1ULL << 0) + (1ULL << 1) + (1ULL << 2) + (1ULL << 3) + (1ULL << 32) + (1ULL << 33) + (1ULL << 34);
+            msr_write(IA32_CR_PERF_GLOBAL_CTRL, value, kv.first);
+        }
+    }
+
 	LOG(info) << "Sensorgroup " << _groupName << " stopped.";
 }
 
@@ -115,15 +136,35 @@ int32_t MSRSensorGroup::msr_write(uint64_t msr_number, uint64_t value, unsigned
 	return pwrite(cpuToFd[cpu], (const void *) &value, sizeof(uint64_t), msr_number);
 }
 
-void MSRSensorGroup::program_fixed(){
+/**
+ * Program the fixed MSR as required for this plugin.
+ *
+ * @return  True if counters programmed successfully, false otherwise, e.g.
+ *          because the counters are already in use.
+ */
+bool MSRSensorGroup::program_fixed(){
+    unsigned failedCpu = 9999;
+
 	for (auto &kv : cpuToFd) {
 		// program core counters
 
+	    //we do not want to interrupt other services already doing measurements with MSRs
+        //therefore check if any fixed counter is currently enabled
 		struct FixedEventControlRegister ctrl_reg;
-		// disable counters while programming
-		msr_write(IA32_CR_PERF_GLOBAL_CTRL, 0, kv.first);
+        std::bitset<64> cur_reg(ctrl_reg.value);
+
 		msr_read(IA32_CR_FIXED_CTR_CTRL, &ctrl_reg.value, kv.first);
 
+		if (cur_reg[0] || cur_reg[1] || cur_reg[4] || cur_reg[5] || cur_reg[8] || cur_reg[9]) {
+		  //at least one is enabled. Do not overwrite them.
+		  //Instead we revert the already programmed counters and return
+		  failedCpu = kv.first;
+		  break;
+		}
+
+		// disable counters while programming
+        msr_write(IA32_CR_PERF_GLOBAL_CTRL, 0, kv.first);
+
 		ctrl_reg.fields.os0 = 1;
 		ctrl_reg.fields.usr0 = 1;
 		ctrl_reg.fields.any_thread0 = 0;
@@ -149,6 +190,25 @@ void MSRSensorGroup::program_fixed(){
 		msr_write(IA32_CR_PERF_GLOBAL_CTRL, value, kv.first);
 	}
 
+	//One of the fixed counters was already enabled.
+	//Reset all counters which were already programmed before returning.
+	if (failedCpu != 9999) {
+	  for (auto& kv : cpuToFd) {
+	    if (kv.first != failedCpu) {
+	      //disable counters before writing anything else
+          msr_write(IA32_CR_PERF_GLOBAL_CTRL, 0, kv.first);
+          //reset all bits to 0
+          msr_write(IA32_CR_FIXED_CTR_CTRL, 0, kv.first);
+          //set all global enable bits to 1
+          uint64_t value = (1ULL << 0) + (1ULL << 1) + (1ULL << 2) + (1ULL << 3) + (1ULL << 32) + (1ULL << 33) + (1ULL << 34);
+          msr_write(IA32_CR_PERF_GLOBAL_CTRL, value, kv.first);
+	    } else {
+	      return false;
+	    }
+	  }
+	}
+
+	return true;
 }
 
 void MSRSensorGroup::addCpu(unsigned int cpu){

src/sensors/msr/MSRSensorGroup.h

@@ -35,7 +35,7 @@ private:
 	void read() override;
 	void readAsync() override;
 
-	void program_fixed();
+	bool program_fixed();
 	std::map<unsigned int,int> cpuToFd;
 	int32_t msr_read(uint64_t msr_number, uint64_t * value, unsigned int cpu);
 	int32_t msr_write(uint64_t msr_number, uint64_t value, unsigned int cpu);