Rework CPU counting

Currently htop does not support offline CPUs and hot-swapping, e.g. via
    echo 0 > /sys/devices/system/cpu/cpu2/online

Split the current single cpuCount variable into activeCPUs and
existingCPUs.

Supersedes: #650
Related: #580

28 files changed, 276 insertions, 148 deletions

diff --git a/Action.c b/Action.c
index 21183e0d..86468635 100644
--- a/Action.c
+++ b/Action.c
@@ -302,7 +302,7 @@ static Htop_Reaction actionSetAffinity(State* st) {
    if (Settings_isReadonly())
       return HTOP_OK;
 
-   if (st->pl->cpuCount == 1)
+   if (st->pl->activeCPUs == 1)
       return HTOP_OK;
 
 #if (defined(HAVE_LIBHWLOC) || defined(HAVE_LINUX_AFFINITY))
diff --git a/Affinity.c b/Affinity.c
index 5a73793b..d48fc9bf 100644
--- a/Affinity.c
+++ b/Affinity.c
@@ -59,7 +59,7 @@ Affinity* Affinity_get(const Process* proc, ProcessList* pl) {
    if (ok) {
       affinity = Affinity_new(pl);
       if (hwloc_bitmap_last(cpuset) == -1) {
-         for (unsigned int i = 0; i < pl->cpuCount; i++) {
+         for (unsigned int i = 0; i < pl->existingCPUs; i++) {
             Affinity_add(affinity, i);
          }
       } else {
@@ -93,7 +93,7 @@ Affinity* Affinity_get(const Process* proc, ProcessList* pl) {
       return NULL;
 
    Affinity* affinity = Affinity_new(pl);
-   for (unsigned int i = 0; i < pl->cpuCount; i++) {
+   for (unsigned int i = 0; i < pl->existingCPUs; i++) {
       if (CPU_ISSET(i, &cpuset)) {
          Affinity_add(affinity, i);
       }
diff --git a/AffinityPanel.c b/AffinityPanel.c
index 25169994..56d8d89c 100644
--- a/AffinityPanel.c
+++ b/AffinityPanel.c
@@ -383,7 +383,8 @@ Panel* AffinityPanel_new(ProcessList* pl, const Affinity* affinity, int* width)
    Panel_setHeader(super, "Use CPUs:");
 
    unsigned int curCpu = 0;
-   for (unsigned int i = 0; i < pl->cpuCount; i++) {
+   for (unsigned int i = 0; i < pl->existingCPUs; i++) {
+      /* TODO: skip offline CPUs */
       char number[16];
       xSnprintf(number, 9, "CPU %d", Settings_cpuId(pl->settings, i));
       unsigned cpu_width = 4 + strlen(number);
@@ -427,7 +428,8 @@ Affinity* AffinityPanel_getAffinity(Panel* super, ProcessList* pl) {
    Affinity_add(affinity, i);
    hwloc_bitmap_foreach_end();
    #else
-   for (unsigned int i = 0; i < this->pl->cpuCount; i++) {
+   for (unsigned int i = 0; i < this->pl->existingCPUs; i++) {
+      /* TODO: skip offline CPUs */
       const MaskItem* item = (const MaskItem*)Vector_get(this->cpuids, i);
       if (item->value) {
          Affinity_add(affinity, item->cpu);
diff --git a/AvailableMetersPanel.c b/AvailableMetersPanel.c
index c098b470..384c8864 100644
--- a/AvailableMetersPanel.c
+++ b/AvailableMetersPanel.c
@@ -94,9 +94,9 @@ const PanelClass AvailableMetersPanel_class = {
 
 // Handle (&CPUMeter_class) entries in the AvailableMetersPanel
 static void AvailableMetersPanel_addCPUMeters(Panel* super, const MeterClass* type, const ProcessList* pl) {
-   if (pl->cpuCount > 1) {
+   if (pl->existingCPUs > 1) {
       Panel_add(super, (Object*) ListItem_new("CPU average", 0));
-      for (unsigned int i = 1; i <= pl->cpuCount; i++) {
+      for (unsigned int i = 1; i <= pl->existingCPUs; i++) {
          char buffer[50];
          xSnprintf(buffer, sizeof(buffer), "%s %d", type->uiName, Settings_cpuId(pl->settings, i - 1));
          Panel_add(super, (Object*) ListItem_new(buffer, i));
diff --git a/CPUMeter.c b/CPUMeter.c
index 0bea79fd..4a061037 100644
--- a/CPUMeter.c
+++ b/CPUMeter.c
@@ -43,7 +43,7 @@ static void CPUMeter_init(Meter* this) {
    unsigned int cpu = this->param;
    if (cpu == 0) {
       Meter_setCaption(this, "Avg");
-   } else if (this->pl->cpuCount > 1) {
+   } else if (this->pl->activeCPUs > 1) {
       char caption[10];
       xSnprintf(caption, sizeof(caption), "%3u", Settings_cpuId(this->pl->settings, cpu - 1));
       Meter_setCaption(this, caption);
@@ -59,21 +59,24 @@ static void CPUMeter_getUiName(const Meter* this, char* buffer, size_t length) {
 }
 
 static void CPUMeter_updateValues(Meter* this) {
+   memset(this->values, 0, sizeof(double) * CPU_METER_ITEMCOUNT);
+
    unsigned int cpu = this->param;
-   if (cpu > this->pl->cpuCount) {
+   if (cpu > this->pl->existingCPUs) {
       xSnprintf(this->txtBuffer, sizeof(this->txtBuffer), "absent");
-      for (uint8_t i = 0; i < this->curItems; i++)
-         this->values[i] = 0;
       return;
    }
-   memset(this->values, 0, sizeof(double) * CPU_METER_ITEMCOUNT);
+
+   double percent = Platform_setCPUValues(this, cpu);
+   if (isnan(percent)) {
+      xSnprintf(this->txtBuffer, sizeof(this->txtBuffer), "offline");
+      return;
+   }
 
    char cpuUsageBuffer[8] = { 0 };
    char cpuFrequencyBuffer[16] = { 0 };
    char cpuTemperatureBuffer[16] = { 0 };
 
-   double percent = Platform_setCPUValues(this, cpu);
-
    if (this->pl->settings->showCPUUsage) {
       xSnprintf(cpuUsageBuffer, sizeof(cpuUsageBuffer), "%.1f%%", percent);
    }
@@ -112,7 +115,7 @@ static void CPUMeter_display(const Object* cast, RichString* out) {
    int len;
    const Meter* this = (const Meter*)cast;
 
-   if (this->param > this->pl->cpuCount) {
+   if (this->param > this->pl->existingCPUs) {
       RichString_appendAscii(out, CRT_colors[METER_TEXT], "absent");
       return;
    }
@@ -206,7 +209,7 @@ static void AllCPUsMeter_updateValues(Meter* this) {
 }
 
 static void CPUMeterCommonInit(Meter* this, int ncol) {
-   unsigned int cpus = this->pl->cpuCount;
+   unsigned int cpus = this->pl->existingCPUs;
    CPUMeterData* data = this->meterData;
    if (!data) {
       data = this->meterData = xMalloc(sizeof(CPUMeterData));
diff --git a/CommandLine.c b/CommandLine.c
index 66df3777..d932bb04 100644
--- a/CommandLine.c
+++ b/CommandLine.c
@@ -295,7 +295,7 @@ int CommandLine_run(const char* name, int argc, char** argv) {
    Hashtable* dm = DynamicMeters_new();
    ProcessList* pl = ProcessList_new(ut, dm, flags.pidMatchList, flags.userId);
 
-   Settings* settings = Settings_new(pl->cpuCount);
+   Settings* settings = Settings_new(pl->activeCPUs);
    pl->settings = settings;
 
    Header* header = Header_new(pl, settings, 2);
diff --git a/LoadAverageMeter.c b/LoadAverageMeter.c
index c91e6a2d..bb3b05ed 100644
--- a/LoadAverageMeter.c
+++ b/LoadAverageMeter.c
@@ -47,12 +47,12 @@ static void LoadAverageMeter_updateValues(Meter* this) {
    if (this->values[0] < 1.0) {
       this->curAttributes = OK_attributes;
       this->total = 1.0;
-   } else if (this->values[0] < this->pl->cpuCount) {
+   } else if (this->values[0] < this->pl->activeCPUs) {
       this->curAttributes = Medium_attributes;
-      this->total = this->pl->cpuCount;
+      this->total = this->pl->activeCPUs;
    } else {
       this->curAttributes = High_attributes;
-      this->total = 2 * this->pl->cpuCount;
+      this->total = 2 * this->pl->activeCPUs;
    }
 
    xSnprintf(this->txtBuffer, sizeof(this->txtBuffer), "%.2f/%.2f/%.2f", this->values[0], this->values[1], this->values[2]);
@@ -79,12 +79,12 @@ static void LoadMeter_updateValues(Meter* this) {
    if (this->values[0] < 1.0) {
       this->curAttributes = OK_attributes;
       this->total = 1.0;
-   } else if (this->values[0] < this->pl->cpuCount) {
+   } else if (this->values[0] < this->pl->activeCPUs) {
       this->curAttributes = Medium_attributes;
-      this->total = this->pl->cpuCount;
+      this->total = this->pl->activeCPUs;
    } else {
       this->curAttributes = High_attributes;
-      this->total = 2 * this->pl->cpuCount;
+      this->total = 2 * this->pl->activeCPUs;
    }
 
    xSnprintf(this->txtBuffer, sizeof(this->txtBuffer), "%.2f", this->values[0]);
diff --git a/Process.c b/Process.c
index 9fc76822..fdc17cb2 100644
--- a/Process.c
+++ b/Process.c
@@ -821,7 +821,7 @@ void Process_writeField(const Process* this, RichString* str, ProcessField field
    case PERCENT_NORM_CPU: {
       float cpuPercentage = this->percent_cpu;
       if (field == PERCENT_NORM_CPU) {
-         cpuPercentage /= this->processList->cpuCount;
+         cpuPercentage /= this->processList->activeCPUs;
       }
       if (cpuPercentage > 999.9F) {
          xSnprintf(buffer, n, "%4u ", (unsigned int)cpuPercentage);
diff --git a/ProcessList.c b/ProcessList.c
index d3a773b3..8ab4d8f6 100644
--- a/ProcessList.c
+++ b/ProcessList.c
@@ -34,7 +34,8 @@ ProcessList* ProcessList_init(ProcessList* this, const ObjectClass* klass, Users
    this->userId = userId;
 
    // set later by platform-specific code
-   this->cpuCount = 0;
+   this->activeCPUs = 0;
+   this->existingCPUs = 0;
    this->monotonicMs = 0;
 
    // always maintain valid realtime timestamps
diff --git a/ProcessList.h b/ProcessList.h
index da4a50da..2b9a5070 100644
--- a/ProcessList.h
+++ b/ProcessList.h
@@ -83,7 +83,8 @@ typedef struct ProcessList_ {
    memory_t usedSwap;
    memory_t cachedSwap;
 
-   unsigned int cpuCount;
+   unsigned int activeCPUs;
+   unsigned int existingCPUs;
 } ProcessList;
 
 ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, Hashtable* pidMatchList, uid_t userId);
diff --git a/TasksMeter.c b/TasksMeter.c
index 3840bf9b..9fb6c804 100644
--- a/TasksMeter.c
+++ b/TasksMeter.c
@@ -28,7 +28,7 @@ static void TasksMeter_updateValues(Meter* this) {
    this->values[0] = pl->kernelThreads;
    this->values[1] = pl->userlandThreads;
    this->values[2] = pl->totalTasks - pl->kernelThreads - pl->userlandThreads;
-   this->values[3] = MINIMUM(pl->runningTasks, pl->cpuCount);
+   this->values[3] = MINIMUM(pl->runningTasks, pl->activeCPUs);
    this->total     = pl->totalTasks;
 
    xSnprintf(this->txtBuffer, sizeof(this->txtBuffer), "%d/%d", (int) this->values[3], (int) this->total);
diff --git a/darwin/DarwinProcessList.c b/darwin/DarwinProcessList.c
index 91d62c4a..e58c3496 100644
--- a/darwin/DarwinProcessList.c
+++ b/darwin/DarwinProcessList.c
@@ -134,7 +134,9 @@ ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, H
    ProcessList_init(&this->super, Class(DarwinProcess), usersTable, dynamicMeters, pidMatchList, userId);
 
    /* Initialize the CPU information */
-   this->super.cpuCount = ProcessList_allocateCPULoadInfo(&this->prev_load);
+   this->super.activeCPUs = ProcessList_allocateCPULoadInfo(&this->prev_load);
+   // TODO: support offline CPUs and hot swapping
+   this->super.existingCPUs = this->super.activeCPUs;
    ProcessList_getHostInfo(&this->host_info);
    ProcessList_allocateCPULoadInfo(&this->curr_load);
 
@@ -184,13 +186,13 @@ void ProcessList_goThroughEntries(ProcessList* super, bool pauseProcessUpdate) {
 
    /* Get the time difference */
    dpl->global_diff = 0;
-   for (unsigned int i = 0; i < dpl->super.cpuCount; ++i) {
+   for (unsigned int i = 0; i < dpl->super.existingCPUs; ++i) {
       for (size_t j = 0; j < CPU_STATE_MAX; ++j) {
          dpl->global_diff += dpl->curr_load[i].cpu_ticks[j] - dpl->prev_load[i].cpu_ticks[j];
       }
    }
 
-   const double time_interval = ticksToNanoseconds(dpl->global_diff) / (double) dpl->super.cpuCount;
+   const double time_interval = ticksToNanoseconds(dpl->global_diff) / (double) dpl->super.activeCPUs;
 
    /* Clear the thread counts */
    super->kernelThreads = 0;
diff --git a/darwin/Platform.c b/darwin/Platform.c
index 3fcf314d..e110f72b 100644
--- a/darwin/Platform.c
+++ b/darwin/Platform.c
@@ -186,21 +186,21 @@ int Platform_getMaxPid() {
 
 static double Platform_setCPUAverageValues(Meter* mtr) {
    const ProcessList* dpl = mtr->pl;
-   unsigned int cpus = dpl->cpuCount;
+   unsigned int activeCPUs = dpl->activeCPUs;
    double sumNice = 0.0;
    double sumNormal = 0.0;
    double sumKernel = 0.0;
    double sumPercent = 0.0;
-   for (unsigned int i = 1; i <= cpus; i++) {
+   for (unsigned int i = 1; i <= dpl->existingCPUs; i++) {
       sumPercent += Platform_setCPUValues(mtr, i);
       sumNice    += mtr->values[CPU_METER_NICE];
       sumNormal  += mtr->values[CPU_METER_NORMAL];
       sumKernel  += mtr->values[CPU_METER_KERNEL];
    }
-   mtr->values[CPU_METER_NICE]   = sumNice   / cpus;
-   mtr->values[CPU_METER_NORMAL] = sumNormal / cpus;
-   mtr->values[CPU_METER_KERNEL] = sumKernel / cpus;
-   return sumPercent / cpus;
+   mtr->values[CPU_METER_NICE]   = sumNice   / activeCPUs;
+   mtr->values[CPU_METER_NORMAL] = sumNormal / activeCPUs;
+   mtr->values[CPU_METER_KERNEL] = sumKernel / activeCPUs;
+   return sumPercent / activeCPUs;
 }
 
 double Platform_setCPUValues(Meter* mtr, unsigned int cpu) {
diff --git a/dragonflybsd/DragonFlyBSDProcessList.c b/dragonflybsd/DragonFlyBSDProcessList.c
index 9bf6ffef..823bde59 100644
--- a/dragonflybsd/DragonFlyBSDProcessList.c
+++ b/dragonflybsd/DragonFlyBSDProcessList.c
@@ -95,13 +95,15 @@ ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, H
       sysctl(MIB_kern_cp_times, 2, dfpl->cp_times_o, &len, NULL, 0);
    }
 
-   pl->cpuCount = MAXIMUM(cpus, 1);
+   pl->existingCPUs = MAXIMUM(cpus, 1);
+   // TODO: support offline CPUs and hot swapping
+   pl->activeCPUs = pl->existingCPUs;
 
    if (cpus == 1 ) {
       dfpl->cpus = xRealloc(dfpl->cpus, sizeof(CPUData));
    } else {
       // on smp we need CPUs + 1 to store averages too (as kernel kindly provides that as well)
-      dfpl->cpus = xRealloc(dfpl->cpus, (pl->cpuCount + 1) * sizeof(CPUData));
+      dfpl->cpus = xRealloc(dfpl->cpus, (pl->existingCPUs + 1) * sizeof(CPUData));
    }
 
    len = sizeof(kernelFScale);
@@ -140,8 +142,8 @@ void ProcessList_delete(ProcessList* this) {
 static inline void DragonFlyBSDProcessList_scanCPUTime(ProcessList* pl) {
    const DragonFlyBSDProcessList* dfpl = (DragonFlyBSDProcessList*) pl;
 
-   unsigned int cpus   = pl->cpuCount;   // actual CPU count
-   unsigned int maxcpu = cpus;           // max iteration (in case we have average + smp)
+   unsigned int cpus   = pl->existingCPUs;  // actual CPU count
+   unsigned int maxcpu = cpus;              // max iteration (in case we have average + smp)
    int cp_times_offset;
 
    assert(cpus > 0);
diff --git a/dragonflybsd/Platform.c b/dragonflybsd/Platform.c
index 39983f08..30fb0031 100644
--- a/dragonflybsd/Platform.c
+++ b/dragonflybsd/Platform.c
@@ -159,7 +159,7 @@ int Platform_getMaxPid() {
 
 double Platform_setCPUValues(Meter* this, unsigned int cpu) {
    const DragonFlyBSDProcessList* fpl = (const DragonFlyBSDProcessList*) this->pl;
-   unsigned int cpus = this->pl->cpuCount;
+   unsigned int cpus = this->pl->activeCPUs;
    const CPUData* cpuData;
 
    if (cpus == 1) {
diff --git a/freebsd/FreeBSDProcessList.c b/freebsd/FreeBSDProcessList.c
index 1478e7b7..8c3f17db 100644
--- a/freebsd/FreeBSDProcessList.c
+++ b/freebsd/FreeBSDProcessList.c
@@ -125,13 +125,15 @@ ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, H
       sysctl(MIB_kern_cp_times, 2, fpl->cp_times_o, &len, NULL, 0);
    }
 
-   pl->cpuCount = MAXIMUM(cpus, 1);
+   pl->existingCPUs = MAXIMUM(cpus, 1);
+   // TODO: support offline CPUs and hot swapping
+   pl->activeCPUs = pl->existingCPUs;
 
    if (cpus == 1 ) {
       fpl->cpus = xRealloc(fpl->cpus, sizeof(CPUData));
    } else {
       // on smp we need CPUs + 1 to store averages too (as kernel kindly provides that as well)
-      fpl->cpus = xRealloc(fpl->cpus, (pl->cpuCount + 1) * sizeof(CPUData));
+      fpl->cpus = xRealloc(fpl->cpus, (pl->existingCPUs + 1) * sizeof(CPUData));
    }
 
 
@@ -169,8 +171,8 @@ void ProcessList_delete(ProcessList* this) {
 static inline void FreeBSDProcessList_scanCPU(ProcessList* pl) {
    const FreeBSDProcessList* fpl = (FreeBSDProcessList*) pl;
 
-   unsigned int cpus   = pl->cpuCount;   // actual CPU count
-   unsigned int maxcpu = cpus;           // max iteration (in case we have average + smp)
+   unsigned int cpus   = pl->existingCPUs; // actual CPU count
+   unsigned int maxcpu = cpus;             // max iteration (in case we have average + smp)
    int cp_times_offset;
 
    assert(cpus > 0);
diff --git a/freebsd/Platform.c b/freebsd/Platform.c
index 73383b28..e27ba9a6 100644
--- a/freebsd/Platform.c
+++ b/freebsd/Platform.c
@@ -181,7 +181,7 @@ int Platform_getMaxPid() {
 
 double Platform_setCPUValues(Meter* this, unsigned int cpu) {
    const FreeBSDProcessList* fpl = (const FreeBSDProcessList*) this->pl;
-   unsigned int cpus = this->pl->cpuCount;
+   unsigned int cpus = this->pl->activeCPUs;
    const CPUData* cpuData;
 
    if (cpus == 1) {
diff --git a/linux/LibSensors.c b/linux/LibSensors.c
index 5780c74f..5a92a351 100644
--- a/linux/LibSensors.c
+++ b/linux/LibSensors.c
@@ -32,10 +32,10 @@ static void* dlopenHandle = NULL;
 
 #endif /* BUILD_STATIC */
 
-int LibSensors_init(FILE* input) {
+int LibSensors_init(void) {
 #ifdef BUILD_STATIC
 
-   return sym_sensors_init(input);
+   return sym_sensors_init(NULL);
 
 #else
 
@@ -69,7 +69,7 @@ int LibSensors_init(FILE* input) {
       #undef resolve
    }
 
-   return sym_sensors_init(input);
+   return sym_sensors_init(NULL);
 
 
 dlfailure:
@@ -99,6 +99,18 @@ void LibSensors_cleanup(void) {
 #endif /* BUILD_STATIC */
 }
 
+int LibSensors_reload(void) {
+#ifndef BUILD_STATIC
+   if (!dlopenHandle) {
+      errno = ENOTSUP;
+      return -1;
+   }
+#endif /* !BUILD_STATIC */
+
+   sym_sensors_cleanup();
+   return sym_sensors_init(NULL);
+}
+
 static int tempDriverPriority(const sensors_chip_name* chip) {
    static const struct TempDriverDefs {
       const char* prefix;
@@ -120,10 +132,10 @@ static int tempDriverPriority(const sensors_chip_name* chip) {
    return -1;
 }
 
-void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
-   assert(cpuCount > 0 && cpuCount < 16384);
-   double data[cpuCount + 1];
-   for (size_t i = 0; i < cpuCount + 1; i++)
+void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int existingCPUs, unsigned int activeCPUs) {
+   assert(existingCPUs > 0 && existingCPUs < 16384);
+   double data[existingCPUs + 1];
+   for (size_t i = 0; i < existingCPUs + 1; i++)
       data[i] = NAN;
 
 #ifndef BUILD_STATIC
@@ -145,7 +157,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
 
       if (priority < topPriority) {
          /* Clear data from lower priority sensor */
-         for (size_t i = 0; i < cpuCount + 1; i++)
+         for (size_t i = 0; i < existingCPUs + 1; i++)
             data[i] = NAN;
       }
 
@@ -166,7 +178,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
          /* Feature name IDs start at 1, adjust to start at 0 to match data indices */
          tempID--;
 
-         if (tempID > cpuCount)
+         if (tempID > existingCPUs)
             continue;
 
          const sensors_subfeature* subFeature = sym_sensors_get_subfeature(chip, feature, SENSORS_SUBFEATURE_TEMP_INPUT);
@@ -190,8 +202,8 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
    }
 
    /* Adjust data for chips not providing a platform temperature */
-   if (coreTempCount + 1 == cpuCount || coreTempCount + 1 == cpuCount / 2) {
-      memmove(&data[1], &data[0], cpuCount * sizeof(*data));
+   if (coreTempCount + 1 == activeCPUs || coreTempCount + 1 == activeCPUs / 2) {
+      memmove(&data[1], &data[0], existingCPUs * sizeof(*data));
       data[0] = NAN;
       coreTempCount++;
 
@@ -200,7 +212,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
 
    /* Only package temperature - copy to all cores */
    if (coreTempCount == 0 && !isnan(data[0])) {
-      for (unsigned int i = 1; i <= cpuCount; i++)
+      for (unsigned int i = 1; i <= existingCPUs; i++)
          data[i] = data[0];
 
       /* No further adjustments */
@@ -210,7 +222,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
    /* No package temperature - set to max core temperature */
    if (isnan(data[0]) && coreTempCount != 0) {
       double maxTemp = NAN;
-      for (unsigned int i = 1; i <= cpuCount; i++) {
+      for (unsigned int i = 1; i <= existingCPUs; i++) {
          if (isnan(data[i]))
             continue;
 
@@ -224,7 +236,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
 
    /* Only temperature for core 0, maybe Ryzen - copy to all other cores */
    if (coreTempCount == 1 && !isnan(data[1])) {
-      for (unsigned int i = 2; i <= cpuCount; i++)
+      for (unsigned int i = 2; i <= existingCPUs; i++)
          data[i] = data[1];
 
       /* No further adjustments */
@@ -232,7 +244,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
    }
 
    /* Half the temperatures, probably HT/SMT - copy to second half */
-   const unsigned int delta = cpuCount / 2;
+   const unsigned int delta = activeCPUs / 2;
    if (coreTempCount == delta) {
       memcpy(&data[delta + 1], &data[1], delta * sizeof(*data));
 
@@ -241,7 +253,7 @@ void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount) {
    }
 
 out:
-   for (unsigned int i = 0; i <= cpuCount; i++)
+   for (unsigned int i = 0; i <= existingCPUs; i++)
       cpus[i].temperature = data[i];
 }
 
diff --git a/linux/LibSensors.h b/linux/LibSensors.h
index f3410175..a4c26e20 100644
--- a/linux/LibSensors.h
+++ b/linux/LibSensors.h
@@ -8,9 +8,10 @@
 #include "linux/LinuxProcessList.h"
 
 
-int LibSensors_init(FILE* input);
+int LibSensors_init(void);
 void LibSensors_cleanup(void);
+int LibSensors_reload(void);
 
-void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int cpuCount);
+void LibSensors_getCPUTemperatures(CPUData* cpus, unsigned int existingCPUs, unsigned int activeCPUs);
 
 #endif /* HEADER_LibSensors */
diff --git a/linux/LinuxProcessList.c b/linux/LinuxProcessList.c
index 406216f6..9fd07051 100644
--- a/linux/LinuxProcessList.c
+++ b/linux/LinuxProcessList.c
@@ -158,30 +158,85 @@ static void LinuxProcessList_initNetlinkSocket(LinuxProcessList* this) {
 
 #endif
 
-static void LinuxProcessList_updateCPUcount(ProcessList* super, FILE* stream) {
+static void LinuxProcessList_updateCPUcount(ProcessList* super) {
+   /* Similiar to get_nprocs_conf(3) / _SC_NPROCESSORS_CONF
+    * https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/getsysstats.c;hb=HEAD
+    */
+
    LinuxProcessList* this = (LinuxProcessList*) super;
+   unsigned int existing = 0, active = 0;
 
-   unsigned int cpus = 0;
-   char buffer[PROC_LINE_LENGTH + 1];
-   while (fgets(buffer, sizeof(buffer), stream)) {
-      if (String_startsWith(buffer, "cpu")) {
-         cpus++;
-      }
+   DIR* dir = opendir("/sys/devices/system/cpu");
+   if (!dir) {
+      super->activeCPUs = 1;
+      super->existingCPUs = 1;
+      this->cpuData = xReallocArray(this->cpuData, 2, sizeof(CPUData));
+      this->cpuData[0].online = true;
+      this->cpuData[1].online = true;
+      return;
    }
 
-   if (cpus == 0)
-      CRT_fatalError("No cpu entry in " PROCSTATFILE);
-   if (cpus == 1)
-      CRT_fatalError("No cpu aggregate or cpuN entry in " PROCSTATFILE);
+   unsigned int currExisting = super->existingCPUs;
+
+   const struct dirent* entry;
+   while ((entry = readdir(dir)) != NULL) {
+      if (entry->d_type != DT_DIR)
+         continue;
+
+      if (!String_startsWith(entry->d_name, "cpu"))
+         continue;
+
+      char *endp;
+      unsigned long int id = strtoul(entry->d_name + 3, &endp, 10);
+      if (id == ULONG_MAX || endp == entry->d_name + 3 || *endp != '\0')
+         continue;
 
-   /* Subtract aggregate cpu entry */
-   cpus--;
+#ifdef HAVE_OPENAT
+      int cpuDirFd = openat(dirfd(dir), entry->d_name, O_DIRECTORY | O_PATH | O_NOFOLLOW);
+      if (cpuDirFd < 0)
+         continue;
+#else
+      char cpuDirFd[4096];
+      xSnprintf(cpuDirFd, sizeof(cpuDirFd), "/sys/devices/system/cpu/%s", entry->d_name);
+#endif
+
+      existing++;
 
-   if (cpus != super->cpuCount || !this->cpus) {
-      super->cpuCount = MAXIMUM(cpus, 1);
-      free(this->cpus);
-      this->cpus = xCalloc(cpus + 1, sizeof(CPUData));
+      /* readdir() iterates with no specific order */
+      unsigned int max = MAXIMUM(existing, id + 1);
+      if (max > currExisting) {
+         this->cpuData = xReallocArray(this->cpuData, max + /* aggregate */ 1, sizeof(CPUData));
+         for (unsigned int j = currExisting; j < max; j++) {
+            this->cpuData[j].online = false;
+         }
+         currExisting = max;
+      }
+
+      char buffer[8];
+      ssize_t res = xReadfileat(cpuDirFd, "online", buffer, sizeof(buffer));
+      /* If the file "online" does not exist or on failure count as active */
+      if (res < 1 || buffer[0] != '0') {
+         active++;
+         this->cpuData[id + 1].online = true;
+      } else {
+         this->cpuData[id + 1].online = false;
+      }
+
+      Compat_openatArgClose(cpuDirFd);
    }
+
+   closedir(dir);
+
+#ifdef HAVE_SENSORS_SENSORS_H
+   /* When started with offline CPUs, libsensors does not monitor those,
+    * even when they become online. */
+   if (super->existingCPUs != 0 && (active > super->activeCPUs || currExisting > super->existingCPUs))
+      LibSensors_reload();
+#endif
+
+   super->activeCPUs = active;
+   assert(existing == currExisting);
+   super->existingCPUs = currExisting;
 }
 
 ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, Hashtable* pidMatchList, uid_t userId) {
@@ -220,15 +275,13 @@ ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, H
       CRT_fatalError("Failed to parse btime from " PROCSTATFILE);
    }
 
+   fclose(statfile);
+
    if (btime == -1)
       CRT_fatalError("No btime in " PROCSTATFILE);
 
-   rewind(statfile);
-
    // Initialize CPU count
-   LinuxProcessList_updateCPUcount(pl, statfile);
-
-   fclose(statfile);
+   LinuxProcessList_updateCPUcount(pl);
 
    return pl;
 }
@@ -236,7 +289,7 @@ ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, H
 void ProcessList_delete(ProcessList* pl) {
    LinuxProcessList* this = (LinuxProcessList*) pl;
    ProcessList_done(pl);
-   free(this->cpus);
+   free(this->cpuData);
    if (this->ttyDrivers) {
       for (int i = 0; this->ttyDrivers[i].path; i++) {
          free(this->ttyDrivers[i].path);
@@ -1270,9 +1323,9 @@ static bool LinuxProcessList_recurseProcTree(LinuxProcessList* this, openat_arg_
       return false;
    }
 
-   unsigned int cpus = pl->cpuCount;
-   bool hideKernelThreads = settings->hideKernelThreads;
-   bool hideUserlandThreads = settings->hideUserlandThreads;
+   const unsigned int activeCPUs = pl->activeCPUs;
+   const bool hideKernelThreads = settings->hideKernelThreads;
+   const bool hideUserlandThreads = settings->hideUserlandThreads;
    while ((entry = readdir(dir)) != NULL) {
       const char* name = entry->d_name;
 
@@ -1407,7 +1460,7 @@ static bool LinuxProcessList_recurseProcTree(LinuxProcessList* this, openat_arg_
 
       /* period might be 0 after system sleep */
       float percent_cpu = (period < 1E-6) ? 0.0F : ((lp->utime + lp->stime - lasttimes) / period * 100.0);
-      proc->percent_cpu = CLAMP(percent_cpu, 0.0F, cpus * 100.0F);
+      proc->percent_cpu = CLAMP(percent_cpu, 0.0F, activeCPUs * 100.0F);
       proc->percent_mem = proc->m_resident / (double)(pl->totalMem) * 100.0;
 
       if (! LinuxProcessList_updateUser(pl, proc, procFd))
@@ -1771,33 +1824,50 @@ static inline void LinuxProcessList_scanZfsArcstats(LinuxProcessList* lpl) {
 static inline double LinuxProcessList_scanCPUTime(ProcessList* super) {
    LinuxProcessList* this = (LinuxProcessList*) super;
 
+   LinuxProcessList_updateCPUcount(super);
+
    FILE* file = fopen(PROCSTATFILE, "r");
    if (!file)
       CRT_fatalError("Cannot open " PROCSTATFILE);
 
-   LinuxProcessList_updateCPUcount(super, file);
-
-   rewind(file);
+   unsigned int existingCPUs = super->existingCPUs;
+   unsigned int lastAdjCpuId = 0;
 
-   unsigned int cpus = super->cpuCount;
-   for (unsigned int i = 0; i <= cpus; i++) {
+   for (unsigned int i = 0; i <= existingCPUs; i++) {
       char buffer[PROC_LINE_LENGTH + 1];
       unsigned long long int usertime, nicetime, systemtime, idletime;
       unsigned long long int ioWait = 0, irq = 0, softIrq = 0, steal = 0, guest = 0, guestnice = 0;
-      // Depending on your kernel version,
-      // 5, 7, 8 or 9 of these fields will be set.
-      // The rest will remain at zero.
+
       const char* ok = fgets(buffer, sizeof(buffer), file);
       if (!ok)
          break;
 
+      // cpu fields are sorted first
+      if (!String_startsWith(buffer, "cpu"))
+         break;