implement no-MSR mode

Author: rdementi

src/cpucounters.cpp

@@ -2505,6 +2505,12 @@ PCM::ErrorCode PCM::program(const PCM::ProgramMode mode_, const void * parameter
         canUsePerf = false;
         if (!silent) std::cerr << "Installed Linux kernel perf does not support hardware top-down level-1 counters. Using direct PMU programming instead.\n";
     }
+
+    if (canUsePerf == false && noMSRMode())
+    {
+        std::cerr << "ERROR: can not use perf driver and no-MSR mode is enabled\n" ;
+        return PCM::UnknownError;
+    }
 #endif
 
     if(allow_multiple_instances)
@@ -3692,9 +3698,9 @@ bool PCM::PMUinUse()
 
         for (uint32 j = 0; j < core_gen_counter_num_max; ++j)
         {
-            MSR[i]->read(IA32_PERFEVTSEL0_ADDR + j, &event_select_reg.value);
+            const auto count = MSR[i]->read(IA32_PERFEVTSEL0_ADDR + j, &event_select_reg.value);
 
-            if (event_select_reg.fields.event_select != 0 || event_select_reg.fields.apic_int != 0)
+            if (count && (event_select_reg.fields.event_select != 0 || event_select_reg.fields.apic_int != 0))
             {
                 std::cerr << "WARNING: Core " << i <<" IA32_PERFEVTSEL" << j << "_ADDR is not zeroed " << event_select_reg.value << "\n";
 
@@ -3710,12 +3716,12 @@ bool PCM::PMUinUse()
         FixedEventControlRegister ctrl_reg;
         ctrl_reg.value = 0xffffffffffffffff;
 
-        MSR[i]->read(IA32_CR_FIXED_CTR_CTRL, &ctrl_reg.value);
+        const auto count = MSR[i]->read(IA32_CR_FIXED_CTR_CTRL, &ctrl_reg.value);
 
         // Check if someone has installed pmi handler on counter overflow.
         // If so, that agent might potentially need to change counter value
         // for the "sample after"-mode messing up PCM measurements
-        if(ctrl_reg.fields.enable_pmi0 || ctrl_reg.fields.enable_pmi1 || ctrl_reg.fields.enable_pmi2)
+        if (count && (ctrl_reg.fields.enable_pmi0 || ctrl_reg.fields.enable_pmi1 || ctrl_reg.fields.enable_pmi2))
         {
             std::cerr << "WARNING: Core " << i << " fixed ctrl:" << ctrl_reg.value << "\n";
             if (needToRestoreNMIWatchdog == false) // if NMI watchdog did not clear the fields, ignore it

src/msr.cpp

@@ -213,8 +213,20 @@ int32 MsrHandle::read(uint64 msr_number, uint64 * value)
 
 #else
 // here comes a Linux version
+
+bool noMSRMode()
+{
+    static int noMSR = -1;
+    if (noMSR < 0)
+    {
+        noMSR = (safe_getenv("PCM_NO_MSR") == std::string("1")) ? 1 : 0;
+    }
+    return 1 == noMSR;
+}
+
 MsrHandle::MsrHandle(uint32 cpu) : fd(-1), cpu_id(cpu)
 {
+    if (noMSRMode()) return;
     constexpr auto allowWritesPath = "/sys/module/msr/parameters/allow_writes";
     static bool writesEnabled = false;
     if (writesEnabled == false)
@@ -237,6 +249,7 @@ MsrHandle::MsrHandle(uint32 cpu) : fd(-1), cpu_id(cpu)
     if (handle < 0)
     {
          std::cerr << "PCM Error: can't open MSR handle for core " << cpu << "\n";
+         std::cerr << "Try no-MSR mode by setting env variable PCM_NO_MSR=1\n";
          throw std::exception();
     }
     fd = handle;
@@ -254,14 +267,21 @@ int32 MsrHandle::write(uint64 msr_number, uint64 value)
     std::lock_guard<std::mutex> g(m);
     std::cout << "DEBUG: writing MSR 0x" << std::hex << msr_number << " value 0x" << value << " on cpu " << std::dec << cpu_id << std::endl;
 #endif
+    if (fd < 0) return 0;
     return ::pwrite(fd, (const void *)&value, sizeof(uint64), msr_number);
 }
 
 int32 MsrHandle::read(uint64 msr_number, uint64 * value)
 {
+    if (fd < 0) return 0;
     return ::pread(fd, (void *)value, sizeof(uint64), msr_number);
 }
 
 #endif
 
+
+#ifndef __linux__
+bool noMSRMode() { return false; }
+#endif
+
 } // namespace pcm

src/msr.h

@@ -35,6 +35,8 @@ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 
 namespace pcm {
 
+bool noMSRMode();
+
 class MsrHandle
 {
 #ifdef _MSC_VER